Title of Invention	SWITCHING ARRANGEMENT AND METHOD FOR OPERATING AN ELECTROMAGNETIC RELAY
Abstract	The invention relates to a switching arrangement for controlling an electromagnetic relay comprising a relay coil (11) and relay contacts, two switching devices (12a, 12b) being arranged in a current path (10) with the relay coil (11). A control device (13) is provided and set up in such a way as to close the two switching devices (12a, 12b) in order to generate a current flow through the relay coil (11), and to open the two switching devices (12a, 12b) in order to interrupt a current flow through the relay coil (11). The aim of the invention is to provide a circuit arrangement and an above-mentioned method. In order to desi gn such a circuit arrangement in such a way that an anticipatory check of the relay coil (11) and the two switching devices (12a, 12b) for errors is enabled, the control device (13) is designed to send test signals (P_A, P_B) to the first and the second switching devices (12a, 12b). A conversion device (l5) is subjected to a measuring voltage (U mess) which is converted into a binary response signal (BS). An error in the relay coil (11) or on of the switching devices (12a, 12b) is displayed when the course of the binary response signal (BS) deviates from an expected course. The invention also relates to a corresponding method for controlling an electro magnetic relay.

Title of Invention

SWITCHING ARRANGEMENT AND METHOD FOR OPERATING AN ELECTROMAGNETIC RELAY

Abstract

The invention relates to a switching arrangement for controlling an electromagnetic relay comprising a relay coil (11) and relay contacts, two switching devices (12a, 12b) being arranged in a current path (10) with the relay coil (11). A control device (13) is provided and set up in such a way as to close the two switching devices (12a, 12b) in order to generate a current flow through the relay coil (11), and to open the two switching devices (12a, 12b) in order to interrupt a current flow through the relay coil (11). The aim of the invention is to provide a circuit arrangement and an above-mentioned method. In order to desi gn such a circuit arrangement in such a way that an anticipatory check of the relay coil (11) and the two switching devices (12a, 12b) for errors is enabled, the control device (13) is designed to send test signals (P_A, P_B) to the first and the second switching devices (12a, 12b). A conversion device (l5) is subjected to a measuring voltage (U mess) which is converted into a binary response signal (BS). An error in the relay coil (11) or on of the switching devices (12a, 12b) is displayed when the course of the binary response signal (BS) deviates from an expected course. The invention also relates to a corresponding method for controlling an electro magnetic relay.

Full Text	Description Switching arrangement and method for operating an electromagnetic relay The invention relates to a switching arrangement for operating an electromagnetic relay which has a relay coil and relay contacts, in which two switching devices are arranged in a current path with the relay coil such that a first switching device is connected to a first connection of the relay coil and a second switching device is connected to a second connection of the relay coil; and a control device is provided, which is designed to close both switching devices in order to produce a current flow through the relay coil, and to open both switching devices in order to interrupt a current flow through the relay coil. The invention relates furthermore to a corresponding method for operating an electromagnetic relay. Electromagnetic relays are frequently used in order to carry out controlled switching operations in electrical appliances. Electromagnetic relays normally comprise a relay coil and at least one pair of electrical relay contacts. When an electric current is applied to the relay coil, then a magnetic field is produced around the relay coil as a result of which - in the case of a self-opening relay - the relay contacts are closed, such that current can flow via the relay contacts. When the current flowing through the relay coil is interrupted again, then the moving part of the relay contacts is moved back to its original position, for example by means of a spring device, thus opening the relay contacts and interrupting the current flow via them. In the case of self-closing relays, the contacts are closed when no current is flowing through the relay coil, and they are opened when current is flowing through it. Electromagnetic relays are normally used where the aim is to switch a comparatively high current on or off in a switching circuit, by means of a comparatively low current from a control circuit. In this case, the electromagnetic relay provides galvanic decoupling between the control circuit and the switching circuit. Electromagnetic relays are used, for example, in electrical protective devices for monitoring electrical power supply systems in order to trip an electrical circuit breaker, by closing the relay contacts of a so-called "command relay", thus interrupting the fault current, in the event of a fault (for example a short circuit) in the electrical power supply system. When electromagnetic relays are used in safety-relevant areas such as these, it is of very major importance to reliably prevent inadvertent switching on or off, in order on the one hand to ensure a high level of safety in the event of a fault, and on the other hand to avoid costly spurious tripping. In order to monitor the state of the relay contacts, it is first of all possible to feed back their actual state, that is to say whether they are open or closed, to the control device of the relay coil. If there is a difference between the nominal state and the actual state of the relay contacts, a fault in the relay operation is deduced. However, such monitoring is comparatively complex because, in this case, the galvanic decoupling achieved by the relay between the control circuit and the switching circuit must be exceeded in order to feed back information relating to the state of the relay contacts. Furthermore, in this case, a fault can be identified only after it has already occurred, that is to say the relay contacts have already assumed an undesirable state. Predictive monitoring is impossible. Efforts have therefore been made to make the control circuit for the relay coil as fail-safe as possible. By way of example, faults in switching devices can occur by melting of the switching contents as a result of an excessively high switching power or excessively high temperature, as a result of which the corresponding switching device is permanently short-circuited. In the case of semiconductor switches, for example transistors, a similar effect is known as so-called "breakdown" of the connections of the semiconductor switch. It is likewise possible, both in the case of mechanical switching devices and semiconductor switches, for the switches to permanently block the current flow because of an internal fault. Furthermore, a fault can also occur in the relay coil itself, as a result of which, for example, current can no longer flow through the relay coil because of a broken line, for example. In order to design the control circuit to be as fail-safe as possible, the relay coil is operated not only via a single switching device, which may be susceptible to faults, but instead of this via two switching devices located in the current path of the relay coil. The relay coil is operated only when both switching devices are closed at the same time. As soon as one switching device has opened, the current flow through the relay coil is interrupted. This achieves relatively high operating reliability with respect to inadvertent activation of the relay coil, since a faulty, permanently short-circuited switching device cannot on its own undesirably activate the relay coil. By way of example, one such switching device is known from German patent specification DE 44 09 287 C1, which discloses a relay coil which has two switching devices in the form of transistors located in one current path. The invention is based on the object of specifying a switching arrangement and a method of the type mentioned initially, which allow predictive checking of the relay coil and of both switching devices for the possible occurrence of faults. With regard to the switching device, this object is achieved by a switching arrangement of the type mentioned initially, in which the control device is designed to transmit test signals to the first and the second switching devices, wherein the test signals are created such that they do not influence the instantaneous state of the relay contacts; a measurement voltage is applied to one input of a conversion device and is tapped off between one connection of the relay coil and one of the switching devices, wherein the conversion device is designed to convert the measurement voltage to a binary response signal; and a monitoring device is connected to one output of the conversion device, evaluates the profile of the binary response signal during the transmission of the test signal by the control device, and indicates a fault in the relay coil or one of the switching devices if the profile of the binary response signal differs from an expected profile. The particular advantage of the switching arrangement according to the invention is that the correct operation of the relay- coil and of the two switching devices can be checked easily even before the relay has carried out a faulty switching operation. This makes it possible to check the relay coil and the two switching devices for possible faults, so to speak predictively. In this context, "predictively" therefore means that the serviceability can be checked without having to carry out a switching operation of the relay contacts. To do this, just a single measurement signal in the form of the measurement voltage is tapped off and monitored, in a comparatively simple manner. A malfunction of the two switching devices or of the relay coil can advantageously be achieved as the relay, both in the switched-on state and in the switched-off state, by applying test signals to the two switching devices which, however, do not influence the instantaneous state of the relay contacts. If a fault is discovered in one of the switching devices or in the relay coil during the monitoring, then an operator of an appliance in which the electromagnetic relay is installed - for example the operator of a corresponding electrical protective device - can be informed of this by a fault message relating to this, as a result of which he can initiate replacement of the assembly fitted with the relay and its control circuit. One advantageous embodiment provides that the two switching devices are semiconductor switches, in particular transistors. Semiconductor switches such as these can be switched on and off particularly quickly and with low switching power levels. Furthermore, a further advantageous embodiment of the switching arrangement according to the invention provides that one connection of in each case one damping capacitor is arranged in the current path of the relay coil, in each case between one connection of the relay coil and one switching device. The damping effect of the capacitors allows the profile of the measurement voltage and therefore the profile of the binary response signal to be extended in time, so as to allow particularly simple evaluation. Furthermore, a further advantageous embodiment of the switch arrangement according to the invention provides that the conversion device has a voltage divider which is arranged in parallel with the current path of the relay coil, and to whose voltage divider tap a measurement voltage is on the one hand applied, and on the other hand the measurement voltage is supplied to an operating input of a further switching device in order to obtain the binary signal. This allows a binary response signal to be produced from the measurement voltage, without a high level of circuit complexity. By way of example, the further switching device may be a semiconductor switch, in particular a MOSFET (metal oxide semiconductor field effect transistor). Field effect transistors are operated by voltages and are therefore, in the present case, particularly highly suitable for converting the measurement voltage to a binary response signal. With regard to the method, the abovementioned object is achieved by a method for operating an electromagnetic relay which has a relay coil and relay contacts, in which two switching devices are closed in order to produce a current flow through the relay coil, and two switching devices are opened in order to interrupt a current flow through the relay coil, wherein the switching devices are arranged in a current path with the relay coil such that the first switching device is connected to a first connection of the relay coil, and the second switching device is connected to a second connection of the relay coil, wherein, in the case of the method according to the invention, the control device emits test signals to the two switching devices, which test signals do not influence the instantaneous state of the relay contacts; a measurement voltage is tapped off between one connection of the relay coil and one of the switching devices; the measurement voltage is converted to a binary response signal; and a fault in the relay coil or in one of the two switching devices is indicated if the profile of the binary response signal differs from an expected profile. The described method advantageously allows predictive checking of the control circuit of the electromagnetic relay. It is furthermore considered to be an advantageous development for test signals which are shorter than the response time of the relay to be emitted to the two switching devices when the relay contacts are in the open state. In this case, the response time of the relay is considered to be that time which a magnetic field produced by the relay coil requires to react to a sudden change in a voltage applied to the relay coil by a change in the switching state of the relay contacts. For example, if the relay coil is switched off when a magnetic field has been formed completely, then the magnetic field decays only after a certain time delay. The state of the relay contacts does not change until the magnetic field strength is no longer adequate to hold the relay contacts in their previous position. If the relay coil is switched on again in good time, then the magnetic field builds up again, and the relay contacts remain in their state, without any change. In the converse situation, a voltage is suddenly applied to the relay coil, through which no current was previously flowing, a magnetic field of the relay coil requires a certain time period before its magnetic field strength is sufficient to operate the relay contacts. If the current flow is interrupted again in good time, then the- state of the relay contacts does not change. The time duration of the test signals must therefore be created such that they are sufficiently short to ensure that no change in the state of the relay contacts occurs, because of the inertia of the building-up or decaying magnetic field of the relay coil. The method according to the invention can be used to check the two switching devices and the relay coil for possible faults both when no current is flowing through the relay coil and when current is flowing through the relay coil. Specifically, for example, a check is carried out when no current is flowing through the relay coil and with the measurement voltage being tapped off between the second connection of the relay coil and the second switching device, by test signals being emitted in the following sequence: a) a test signal is emitted to the second switching device; b) no test signal is emitted during a signal pause; c) a test signal is emitted to the first switching device. When the measurement voltage is tapped off between the first connection of the relay coil and the first switching device, the distribution of the test signals between the switching devices is correspondingly reversed. When current is flowing through the relay coil, a check can be carried out according to one advantageous development by permanently operating the first switching device, while the second switching device is operated via a pulsed test signal. By way of example, the time profile of the binary response signal can be continuously compared with the expected profile. However, one particularly advantageous embodiment of the method according to the invention provides that in order to determine whether there is a fault in the relay coil or one of the switching devices, the binary response signal is compared with the expected profile at at least two characteristic times, wherein at least one change relating to the state of at least one signal has taken place between the characteristic times. In this embodiment, the monitoring device's computation power which is required for the comparative process is kept relatively minor, since the profile of the binary response signal and the expected profile need in the simplest case be compared with one another at only two particularly characteristic times, and in consequence there is no need for continuous comparison. Since a 100% match between the binary response signal and the expected profile can normally be achieved only with difficulty in any case, a further advantage of this embodiment is that, if the times under consideration are chosen sensibly - specifically sufficiently far away from those times at which a change in the test signals occurs - insignificant differences between the profile of the binary response signal and the expected profile will not lead to a fault message. In order to allow the two switching devices and the relay coil to be monitored continuously for possible faults, the method according to the invention should be repeated at regular time intervals. The control device advantageously emits different test signals, depending on the state of the relay contacts. The invention will be explained in more detail in the following text with reference to exemplary embodiments. In this case: Figure 1 shows a schematic block diagram of one general embodiment of a switching arrangement for operating an electromagnetic relay, Figure 2 shows a circuit diagram of one possible embodiment of a switching arrangement for operating an electromagnetic relay, Figure 3 shows a plurality of diagrams in order to explain examples of test signals and the measurement voltages caused by them, and binary response signals, when the relay coil is checked without any current flowing through it, Figure 4 shows a method flowchart in order to explain one exemplary embodiment of a check with no current flowing through the relay coil, Figure 5 shows a monitoring test signal sequence with no current flowing through the relay coil, Figure 6 shows a plurality of diagrams in order to explain examples of test signals and the measurement voltages caused by them, and binary response signals when the relay coil is checked with current flowing through it, and Figure 7 shows a method flowchart in order to explain one exemplary embodiment of a check with current flowing through the relay coil. Figure 1 shows a schematic block diagram of one exemplary embodiment of a switching arrangement for operating an electromagnetic relay. A control circuit for the electromagnetic relay comprises a series circuit in a current path 10 of a relay coil 11 with a first switching device 12a and a second switching device 12b, with the switching devices 12a and 12b being symbolized, just by way of example, by mechanical switching devices in figure 1. The switching devices 12a and 12b may be formed by mechanical switches or semiconductor switches, such as transistors. A high and a low voltage level are respectively indicated by "V+" and "V-". By way of example, the high voltage level V+ may be 10V, while the low voltage level V- is 0V. The first switching device 12a is connected to a first connection 11a of the relay coil 11 on the side with the high voltage level, V+, while the second switching device 12b is connected to a second connection l1b of the relay coil 11 on the side with the low voltage level V-. The control inputs of the first and the second switching devices 12a and 12b are connected to a control device 13 . The switching devices 12a and 12b can be switched on and off via the control device 13. The control device 13 is designed to emit test signals to the control inputs of the first and second switching devices 12a and 12b, as will be explained in more detail later. A measurement voltage Umeas is tapped off via a branch 14 at the connection of the second connection 11b of the relay coil 11 to the second switching device 12b, and is supplied to a conversion device 15. The conversion device 15 is designed to convert the measurement voltage Umeas to a binary response signal BS, and to emit this at its output. The binary response signal BS is supplied to a monitoring device 16, which can interchange information with the control device 13 . The monitoring device 16 may either form an autonomous unit - as illustrated in figure 1 - or else may be integrated in the control device 13, - although this is not illustrated in figure 1. Both the control device 13 and the monitoring device 16 may have a microprocessor or some other logic module (for example an ASIC) which controls its operation. Although this is not illustrated in figure 1, the measurement voltage Umeas can also be arranged at the connection between the first switching device 12a and the first connection of the relay coil 11. The sequence of the test signals for monitoring the current path 10, as described in the following text, should in a situation such as this be subdivided in a correspondingly reversed manner between the two switching devices 12a and 12b, and the fault situations described below should likewise be appropriately adapted. However, the following examples are intended to be based on the measurement voltage Umeas being tapped off as shown in figure 1, that is to say between the second switching device 12b and the second connection of the relay coil 11. In one possible more specific embodiment, a switching arrangement for operating an electromagnetic relay may be designed, for example, as shown in figure 2. The same reference symbols are used in figure 2 for components corresponding to figure 1. Figure 2 shows a relay coil 11 whose first connection 11a on the side with the high voltage level V+ is connected to a first switching device 12a, while the second connection 11b of the relay coil 11 on the side with the low voltage level V- is connected to a second switching device 12b. By way of example, the switching devices 12a and 12b are illustrated in figure 2 as semiconductor switches in the form of transistors. A dashed-line boundary indicates a group of switching elements corresponding to the conversion device 15 shown in figure 1. The core piece of the conversion device 15 in the embodiment shown in figure 2 is formed by a voltage divider 22 which, for example, comprises two non-reactive resistors 22a and 22b. A voltage divider tap 23 is located between the two non-reactive resistors 22a and 22b and is connected on the one hand to the branch 14 for the measurement voltage, and on the other hand to a control input of a further switching device 24. A series circuit 25 is arranged in parallel with the relay coil 11 and the switching device 12a, is composed of a non-reactive resistor 25a and a diode 25b, and is used to cope with overvoltages which can occur when the current flow through the relay coil 11 is interrupted. A further non-reactive resistor 26 is used to set the voltage level of the binary response signal BS. One connection of a first damping capacitor 27a is connected to the first connection 11a of the relay coil 11 at the connection of the first switching device 12a, and its other connection is at the low voltage level V-. A second damping capacitor 27b is connected in a corresponding manner by its first connection to the connection between the second switching device 12b and the second connection 11b of the relay coil 11, and its second connection is likewise at the low voltage level V-. The method of operation of the switching arrangement illustrated in figure 2 will be explained in more detail in the following text, in particular with reference to the checking of the two switching devices 12a and 12b and of the relay coil 11 for possible faults. Reference will also be made to figures 3 to 7, in addition to figure 2, for this purpose. The control device 13 is first of all used to produce a current flow through the relay coil 1, or to interrupt it, by simultaneously opening or respectively closing the switching devices 12a and 12b. Simultaneously closing the two switching devices 12a and 12b results in a current flow through the relay coil 11, as a result of which a corresponding magnetic field is developed in the relay coil 11 and, beyond a certain magnetic field strength, results in a change in the state of the relay contacts (not illustrated) of the electromagnetic relay. In order to interrupt the current flow in the relay coil, the control device 13 opens the two switching devices 12a and 12b, as a result of which the magnetic field produced by the relay coil 11 decays again. When the field strength produced by the magnetic field is no longer sufficient to keep the relay contacts in their position, they change over to their normal position - for example by the influence of spring force. In the situation when a fault is present in one of the two switching devices 12a and 12b or the relay coil 11, it is no longer possible to ensure correct operation of the relay coil 11 and therefore of the switching circuit arranged at the relay contacts. For the situation in the example, in which the electromagnetic relay is a command relay for operating an electrical circuit breaker, a malfunction such as this can, for example, cause undesirable spurious tripping of the circuit breaker, or intended tripping of the circuit breaker may be prevented. The current path 10 comprising the two switching devices 12a and 12b of the relay coil is checked for this reason. Irrespective of whether or not current is flowing through the relay coil 11, the control device 13 emits different test signals P_A, P_B to the switching devices 12a and 12b, resulting in a change in the voltage level at the branch 14. The measurement voltage Umeas that is present at this branch 14 is supplied to the conversion device 15, where it is converted to a binary response signal BS. The profile of the binary response signal BS is compared by the monitoring device 16 with an expected profile, and a fault in the current path 10 is identified if the expected profile and the actual profile of the binary response signal BS differ from one another. In order to allow the expected profile and the actual profile of the binary response signal BS to be compared with one another, the monitoring device 16 is able to interchange information with the control device 13 in order, for example, to be informed of the start of the sending of the test signals P_A, P_B to the two switching devices 12a and 12b. When the monitoring device 16 identifies a fault in the current path 10, an appropriate fault message can be emitted which informs an operator of an appliance in which the electromagnetic relay is installed of the fault. The operator of the appropriate appliance can then replace the corresponding faulty assembly even before the electromagnetic relay can actually malfunction. A check of the current path 10 for possible faults can be carried out with or without current flowing through the relay coil, and correspondingly with the relay contacts switched off or switched on, without having to influence the state of the relay contacts in the process. Figures 2, 3 and 4 will first of all be used to explain in the following text how the current path 10 is checked when (deliberately) no current is flowing through the relay coil. For this purpose, the two upper diagrams in figure 3 show the profiles of the test signals P_A and P_B, while the following ten diagrams, in each case on the left-hand side, show the measurement voltages which are present at the branch 14 when no faults are present and for various fault situations, while the right-hand side in each case shows the binary response signals, which result from the respective measurement voltages, when no fault is present and for various fault situations. As can be seen from figure 3, a test signal P_B is first of all supplied to the second switching device, in order to start a test process. This test signal P_B switches the second switching device 12B to its closed state. In this case, the duration of the test signal P_B is chosen such that, even in the situation in which the first switching device 12a has been permanently short-circuited because of a fault, the duration of a current flow which then results through the relay coil 11 has no effect on the state of the relay contacts. The duration of the test signal P_B must therefore be less than the response time, as already explained earlier, of the relay. Normally, the duration of a test signal is for this purpose chosen to be between a lower and an upper limit, with the lower limit indicating that time which is required to generate a correct binary response signal in the conversion device 15, and the upper limit allowing an adequately safe margin from the response time of the relay. By way of example, the possible range for the time duration of the test signals are between approximately 40 and approximately 200 us. As can be seen from figure 3, the emission of the test signal P_B to the second switching device 12b is ended again after a short time period chosen in this way, and this is followed by a signal pause, during which no test signal is emitted to the switching devices 12a or 12b. The switching pause is followed by a further test signal P_A to be emitted to the first switching device 12a, causing the switching device 12a to close. The time duration of the test signal P_A must also be chosen to be sufficiently short that the state of the relay contacts is not influenced even if the second switching device 12b is in a permanently short-circuited state because of the fault. The time duration of the test signal P_A must therefore also be shorter than the response time of the relay. The test process is ended after the end of this test signal sequence; a further test process can be started after a pause of any defined length. For example, it is possible for another test process to be initiated every 250 us. The diagrams arranged in the second line of figure 3 show the profile of the measurement voltage in the situation when both the switching devices 12a and 12b and the relay coil 11 are in a correct, that is to say fault-free, state (corr = correct). The profile of the measurement voltage will now be explained with reference to figure 2. This is based on the assumption that the two switching devices 12a and 12b are operating correctly and they are both first of all in the switched-off state. Initially, the measurement voltage is at a mid-voltage level, which is predetermined by the voltage divider 22. The binary response signal is at a high level, since the measurement voltage is sufficient to switch on the further switching device 24. The emission of the test signal P_B to the second switching device 12b closes the switching device 12b, and the measurement voltage at the branch 14 is drawn to the low voltage level V-, since the second switching device 12b bridges the lower resistor 22b in the voltage divider 22. The profile of the measurement voltage in figure 3 thus exhibits a sudden fall, as soon as the test signal P_B closes the switching device 12b. In a corresponding manner, the binary response signal BScorr falls to a low level, since the further switching device is switched off because of the low measurement voltage applied to it. When the test signal P_B ends, the second switching device 12b returns to the switched-off state, and the previously discharged damping capacitors 27a and 27b are charged via the upper resistor 22a in the voltage divider 22. If the damping capacitors 27a and 27b and the non-reactive resistor 22a in the voltage divider are of adequate size, this charging process takes place sufficiently slowly but virtually no rise in the measurement voltage is perceptible toward the signal pause. The rise in the measurement voltage is at least not sufficient to change the further switching device 24 in the conversion device 15 to its state in which current is passed through, as a result of which the binary response signal BScorr still remains at the low level during the signal pause. When the test signal P_A acts on the first switching device 12a after the signal pause, and this switching device 12a is switched to its state in which current passes through it, the damper capacitors 27a and 27b are charged comparatively quickly, since the upper resistor 22a in the voltage divider 22 is bridged, and the high voltage level V+ is applied directly to the damping capacitors 27a and 27b. This rapid charging process can also be seen from the profile of the measurement voltage which rises rapidly while the second measurement signal P_A is being emitted. Finally, the measurement voltage is at the high voltage level V+. As soon as the measurement voltage has reached a level which causes the further switching device 24 to switch on, the binary response signal rises suddenly to its high level. When the emission of the first test signal P_A ends after the appropriate time period has elapsed, the mid-voltage level, which is predetermined by the voltage divider 22, is assumed again at the branch 14, after the damping capacitors 27a and 27b have discharged via the lower resistor 22b in the voltage divider 22. As already explained in conjunction with figure 2, the binary response signal is transmitted to the monitoring device 16, which compares the profile of the binary response signal with an expected profile. A comparison such as this can be carried out either continuously throughout the entire test process, or can be carried out discontinuously only at specific characteristic times in order on the one hand to save computation capacity in the monitoring device and on the other hand to be insensitive to insignificant differences between the binary response signal and the expected profile, which would not indicate a fault in the current path 10. For this purpose, figure 3 shows two monitoring times t1 and t2, which are each indicated by circles in the profile of the binary response signals. In consequence, for the correct profile of the binary response signal, the signal level must be low at the measurement time t1, and must be high at the measurement time t2. If the monitoring device 16 identifies the correct profile on the basis of the signal levels measured at these times, then it deduces that there are no faults in the current path 10, and does not carry- out any further actions, until the next test process is initiated. The profiles of the respective measurement voltages and of the binary response signals which result from them will be discussed in the following text for fault situations in which one of the two switching devices 12a or 12b is permanently short-circuited or permanently switched off, or there is a broken line in the relay coil 11. First of all, the fault situation F1 will be considered, in which the second switching device 12b is permanently switched off because of a fault. In this situation, the emission of a test signal P_B to the second switching device 12b has no effect whatsoever since the permanently switched off switching device 12b cannot be changed to the switched-on state in this way. In consequence, the corresponding measurement voltage remains at the mid-voltage level set by the voltage divider 22 and it does not fall, as expected according to the profile of the correct measurement voltage indicated by a dashed line, to the low voltage level V-. Correspondingly, the binary response signal BSF1 remains at its high level. During the signal pause, no test signal is emitted to the switching devices 12a or 12b, as a result of which the measurement voltage and the resultant binary response signal BSF1 correspondingly do not change. The emission of the test signal P_A to the first switching device 12a switches it to its switched-on state - since it is operating correctly - as a result of which the measurement voltage which is present at the branch 14 rises to the high voltage level V+ after charging of the damping capacitors 27a and 27b. However, this increase in the measurement voltage to the high voltage level V+ has no effect on the profile of the binary response signal BSF1, because the binary response signal BSF1 is already at its high level. After the end of the test signal P_A, the first switching device 12a is switched off again and the damping capacitors 27a and 27b are discharged to the mid-voltage level which is predetermined by the voltage divider 22. In consequence, the monitoring device 16 detects a binary response signal BSF1 which is permanently at the high level throughout the test process. In the case of a discontinuous analysis of the times t1 and t2, the monitoring device 16 identifies a difference between the binary response signal BSF1 and the expected profile (indicated by a dashed line) at the time t1, since the binary response signal BSF1 is at a high level and is not, as expected, at a low level. From this, the monitoring device 16 deduces that there is a fault in the current path 10, and emits a fault signal in order to warn the operator of an electrical appliance containing the electromagnetic relay. The fault situation F2 will be considered next, in which the second switching device 12b is permanently short-circuited, as a result of which current can flow continuously via the switching device 12b. The measurement voltage which is present at the branch 14 in this situation is already at the low level voltage V- before the start of the test process, because of the short-circuited switching device 12b. Switching on the test signal P_B has no influence on this, since the switching device is in the open state in any case. The resultant binary response signal BSF2 is in consequence permanently at its low level before the start of the test process and while the test signal P_B is being emitted. During the signal pause, the state of both the measurement voltage that of the binary response signal BSF2 do not change, since the short-circuited switching device 12b keeps the branch 14 permanently at the low voltage level V-. The emission of the test signal P_A to the first switching device 12a changes nothing relating to this, either; the branch 14 remains permanently at the low voltage level V- as a result of the short-circuited switching device 12b, even when the switching device 12a is closed. This fault situation F2 illustrates the importance of the time duration of the test signals since, if the test signal P_A were chosen to be too long, the response time of the relay would be exceeded if the switching device 12b were to be permanently short-circuited, and the state of the relay contacts would therefore change undesirably. Emitting the test signal P_A for a correspondingly short time is the only way to ensure that, although on the one hand it is possible to detect the binary signals BSF2, the response time of the relay is, on the other hand, not exceeded, so that the state of the relay contacts does not change. In this fault situation F2, the monitoring device 16 is supplied with a binary response signal BSF2 which is permanently at the low level. If the binary response signal BE?1 is analyzed discretely at the times t1 and t2, a difference will be found at the time t2, where the binary response signal BSF2 is at the low level, instead of at the expected high level. The monitoring device 16 therefore emits a fault signal in order to indicate a fault in the current path 10. The next fault situation F3 comprises both faults, in which the switching device 12a is switched off permanently and there is a broken line in the relay coil 11 (or both) , such that no current can flow via the relay coil 11. In this case, the measurement voltage starts at the mid-voltage potential, which is predetermined by the voltage divider 22, and, on emission of the test signal P_B, falls to the low voltage level because the second switching device 12b is then short-circuited. In a corresponding manner, the binary response signal BSF3 falls to its low level. During the signal pause, the damping capacitor 27b (in the event of a broken line in the relay coil 11) or both damping capacitors 27a and 27b (if the first switching device 12a is permanently switched off) is or are charged again via the upper resistor 22a in the voltage divider 22, with this charging process taking place sufficiently slowly, as already mentioned, that the state of the further switching device 24 does not change. In consequence, the binary response signal BSF3 remains at the low level. Since, in the fault situation F3 under consideration here, either the first switching device 12a or the relay coil 11 (or both) 'are or is switched off permanently, the emission of a test signal P_A to the first switching device 12a cannot produce any current flow through the switching device 12a and the relay coil 11, as a result of which the process of charging the damping capacitors 27a and 27b via the resistor 22a continues correspondingly slowly, as a result of which the measurement voltage which is present at the branch 14 is also not sufficient to switch on the further switching device 24 while the test signal P_A is being emitted. In consequence, the binary response signal BSF3 remains at the low level. The monitoring device 16 is supplied with a low level of the binary response signal BSF3 at each of the times t1 and t2, as a result of which a difference from the expected profile is found at the time t2, and a fault signal is emitted. Finally, the fault situation F4 will be considered, in which the first switching device 12a is permanently short-circuited. Since, in this case, the upper resistor 22a in the voltage divider 22 is permanently bridged, the measurement voltage in this case starts at the high voltage level V+ even before the start of the test process. The binary response signal BSF4 is correspondingly at the high level. Emission of the test signal P_B closes the second switching device 12b, and the voltage level at the branch 14 therefore falls to the low voltage level V-. This sudden change can be seen from the profile of the measurement voltage and also from the binary response signal BSF4 which results from this. After the end of the test signal P_B, the second switching device 12b once again is switched off, as a result of which the capacitors 27a and 27b are charged very quickly to the high voltage level V+ via the permanently short-circuited switching device 12a. In consequence, the binary response signal BSF4 jumps to the high level again even during the signal pause. In consequence, emission of the test signal P_A to the first switching device 12a has no more effect whatsoever on the measurement voltage and on the binary response signal BSF4 resulting from this, since the first switching device 12a is permanently short-circuited in any case, and the branch 14 is already at the high voltage level V+. In consequence, in this fault situation, the monitoring device 16 is supplied with the profile of the binary response signal BSF4 as illustrated in figure 3. Even when the times t1 and t2 are considered discretely, the monitoring device 16 identifies a difference between the binary response signal BEF4 and the expected profile at the time t1, and emits a fault signal. Figure 4 illustrates the timing of the test process for discontinuous testing at the times t1 and t4, once again in a summarized form on the basis of a method flowchart. After the start of the test process ("TEST Start"), the test signal P_B is first of all emitted to the second switching device 12b by the control device 13, in step 40. A wait from a specific time period, for example 40 us, takes place according to step 41, before the second test signal P_B is switched off again in step 42. A wait for a predetermined time period, for example 40 us again, once again takes place during the signal pause in step 43, during which no test signal is emitted. Once this time period has elapsed, a check is carried out in step 44 to determined whether the binary response signal is at the expected low level (annotated "0" in figure 4). If this is not the case, a fault message is emitted. However, if the check in step 44 shows that the binary response signal is at the expected low level, then the test signal P_A is switched on according to step 45, in order to switch on the switching device 12a. The test signal P_A is maintained in step 46 for a predetermined time period, for example of 40 us again, before the monitoring device 16 checks, in step 47, whether the binary response signal is at the expected high level (the high level is annotated "1" by way of example, in figure 4). If a binary response signal difference is found, a fault message is once again emitted. If a correct binary response signal is identified, then the test signal P_A is switched off in a next step 48, and the test process is successfully completed ("TEST OK") . After a predetermined time period has elapsed, the test process can be initiated once again by activating the sequence "TEST Start", in order to ensure continuous testing of the current path 10. The monitoring of the current path 10 for the situation in which (deliberately) current is flowing through the relay coil 11 will now be described with reference to figures 5 to 7. In this case as well, there is once again a requirement for the check to have no influence whatsoever on the state of the relay contacts. The switching-on and holding process of the electromagnetic relay is illustrated first of all in figure 5. As is known, a relay coil requires more power to be supplied to it in order to operate the relay contacts, for example while the relay contacts are being switched on, and is required to hold the relay contacts in their operated position. In consequence, the two switching devices 12a and 12b are first of all switched on at the same time at the time to, in order to move the relay contacts. The simultaneous operation of both switching devices 12a and 12b ensures a permanently high current flow through the relay coil 11, as a result of which the contacts can be quickly moved to their activated position. This activation phase of the relay contacts lasts, as shown in figure 5, from the starting time to to the time t, at which the relay contacts have been moved to their activated state. A so-called pulse-width-modulated holding current can then be passed through the relay coil 11 by pulsed operation of the second switching device 12b, producing less power, averaged over time (and therefore also less power loss in the relay coil), and which is adequate to hold the relay contacts in their activated state. Once again, in this case as well, the inertia of the electromagnetic relay is used since - as already described above - the magnetic field in the relay coil 11 does not decay until after a certain response time to such an extent that the relay contacts would once again change to their deactivated state, such that this response time is always undershot, and the relay contacts remain permanently in their activated state, if the pulses are appropriately short. This procedure of providing a lower holding current overall for the electromagnetic relay by a pulse-width-modulated current flow in the relay coil 11, is already known per se. The operation of the second switching device 12b, which is pulsed in any case, is now advantageously also used as the pulsed test signal P_B for monitoring the corresponding measurement voltage Umeas at the branch 14, in order to monitor the current path 10. For explanatory purposes relating to this, each of the two upper diagrams in figure 6 shows the profile of the test signals P_A and P_B while the test signal P_B is being pulsed, and this is emphasized by a border in figure 5. In this case, the test signal P_A is emitted continuously, while the test signal P_B is emitted in a pulsed form. The correct profile of the measurement voltage and the correct profile of the binary response signal BScorr resulting from this are illustrated in the second line of the two diagrams in figure 6. The profile of the measurement voltage and the binary response signal BScorr* will be explained with reference to figure 2. For the situation in which both the two switching devices 12a and 12b as well as the relay coil 11 are fault-free, the switching device 12a is in its closed state at the start of the test sequence, while the switching device 12b is switched off, because there is no test signal P_B. In consequence, the high voltage level V+ is produced at the branch 14, which is produced by switching on the further switching device 24, and the binary response signal BScorr is in consequence at the high level. When the test signal P_B is emitted, the switching device 12b, which is then closed, draws the measurement voltage the branch 14 to the lower voltage level V-, since in this case the lower resistor 22b in the voltage divider 22 is bridged. Both the measurement voltage and the binary response signal BScorr* which results from it correspondingly fall suddenly. As long as the test signal P_B is emitted, the measurement voltage remains at the low voltage level V-, and the binary response signal BScorr remains at the low level. When the test signal p_B ends, the second switching device 12b is switched off again. The sudden interruption in the current flow in the relay coil 11 and the magnetic field decay resulting from this induce an overvoltage, which decays slowly via the current flowing through the resistor 25a and the diode 25b. The measurement voltage tapped off at the branch 14 correspondingly first of all rises above the high voltage level V+, and then falls gradually to the high voltage level V+ again. Before the current were to fall below the holding current again, with the magnetic field strength therefore no longer being adequate to hold the relay contacts in their activated position, the test signal P_B must be switched on again, in order to close the current path 10 again. The measurement voltage illustrated in figure 6 in consequence results in a binary response signal BScorr* which, after the end of the emission of the test signal P_B, once again changes to its high level again, because the measurement voltage then rises. The monitoring device 16 is supplied with the profile of the binary response signal BS. As when no current is flowing through the relay coil, the correct profile of the binary response signal can be tested continuously or discontinuously. Figure 6 shows two characteristic times t3 and t4 for the discontinuous analysis, at which the monitoring device 16 checks the profile of the binary response signal. If the profile of the binary response signal is correct, corresponding to BScorr*, a low level must in consequence be identified at the time t3, and a high level at the time t4. The fault situations which can possibly be identified, specifically a permanently short-circuited or a permanently switched-off switching device 12b, a permanently switched-off switching device 12a or a broken line in the relay coil 11, will now be explained in the following text. Since the switching device 12a is in any case permanently held in its closed state by the emission of a continuous test signal P_A, the test sequence when current is flowing through the relay coil 11 cannot identify the state in which the first switching device 12a is permanently short-circuited as a result of a fault. However, since this would not initially lead to any malfunction of the electromagnetic relay - the first switching device 12a should be permanently short-circuited in any case - the lack of capability to identify a fault such as this is not a disadvantage of the test process. It will be simple to identify a fault such as this during the check, as already described above, when no current is flowing through the relay coil. The fault situation F5 will be dealt with first of all, in which the second switching device 12b is in a permanently switched-off state. In a situation such as this, the branch 14 would remain permanently at the high voltage level V+ because of the deliberately short-circuited switching device 12a. Since emission of the test signal P_B has no influence on the switching state of the second switching device 12b, because this second switching device 12b is permanently switched off because of the fault, the measurement voltage at the branch 14 remains at the high voltage level V+ irrespective of the state of the test signal P_B. The binary response signal BSF5 which results from this in consequence remains continuously at the high level, as a result of which the monitoring device 16 finds a difference between the profile of the binary response signal BSF5 and the expected profile. In the case of the discontinuous analysis at the times t3 and t4, the monitoring device 16 finds a difference in the binary response signal BSF5 at the time t3, with the response signal being at the high level rather than the low level, and can generate a fault signal. The fault situation F6 will be dealt with next, in which the second switching device 12b is permanently short-circuited. In this case, the measurement voltage at the branch 14 is continuously at the low voltage level V- because the switching device 12b is permanently short-circuited, thus resulting in the profile of the measurement voltage as shown in figure 6. In this case, the measurement voltage is at the low voltage level V- irrespective of the test signal P_B, as a result of which the resultant binary response signal BSF6 also remains permanently at the low level. The monitoring device 16 can in consequence detect a difference from the expected profile both in continuous monitoring and discontinuous monitoring of the profile of the binary response signal; in the case of discontinuous analysis, the monitoring device 16 identifies a low level of the binary response signal BSF6 instead of an expected high level at the time t4, as a result of which a fault signal can be emitted. Finally, the fault situation F7 will be considered, in which either the relay coil 11 has a broken line or the first switching device 12a is switched off permanently. In this case, the measurement voltage at the branch 14 first of all starts at a mid-voltage level, which is set via the voltage divider 22, since the second switching device 12b also prevents current from flowing. The binary response signal BSF7 in consequence starts at the high level. After the test signal P_B has been switched on, and the second switching device 12b has in consequence between closed, the measurement voltage the branch 14 is drawn to the low voltage level V-. This also results in the binary response signal BSF7 falling to the low level. The measurement voltage remains at the low voltage level V-, for as long as the test signal P_B holds the second switching device 12b in the closed state. After the end of the test signal P_B, the damping capacitor 27b (in the event of a broken line in the relay coil 11) or both damping capacitors (in the event of the first switching device 12a being switched off permanently) is or are once again charged to the mid- voltage level through the upper resistor 22a in the voltage divider 22. However, once again, this takes place correspondingly slowly, as a result of which the binary response signal BSF7 initially remains at the low level. The monitoring device 16 therefore identifies a difference between the binary response signal BSF7 and the expected profile. In discontinuous analysis, the monitoring device 16 identifies a low level instead of an expected high level of the binary response signal at the time t4, and can emit a fault signal. Finally, figure 7 shows the procedure for the test process when current is flowing through the relay coil 11, for discontinuous monitoring of the binary response signal at the times t3 and t4. After initiation of the test process ("TEST Start"), the test signal P_B is switched on in a first step 71. After waiting for a short time period to pass in step 72, a check is carried out in step 73 to determine whether the binary response signal BS has assumed a low level ("0") . The time period required in step 72 may be chosen only to be sufficiently long that the reaction of the binary response signal BS to the second switching device 12b being switched on by the test signal P_B can be detected correctly. A fault message is emitted if a difference is found between the binary response signal BS and the expected low level at the time t3 in step 73. However, if the binary response signal BS in step 73 corresponds to the expected profile, then, after a time period which is sufficient to produce the required holding current has elapsed in step 74, the test signal P_B is switched off again in step 75, and waiting takes place for a further short time period in step 76, which time period is chosen such that a reaction of the binary response signal can be detected. A check is carried out in step 77 to determine whether the binary response signal BS is at the expected high level. If this is not the case, a fault is once again emitted. However, if the binary response signal is at the expected high level, then the test process is successfully ended, and can be started once again after a predetermined time period has elapsed. The information interchange that this makes possible between the control device 13 and the monitoring device 16 makes it possible for the monitoring device 16 to include the expected profile of the binary response signal, as appropriate for the respective nominal state of the relay coil 11 (either with or without current flowing through it) in its check. Finally, it should also be mentioned that, in the case of discontinuous checking each of two characteristic measurement times, accurate fault differentiation is not possible all the time, depending on the nature of the fault that has occurred, since a plurality of fault types at the characteristic times generally indicate mutually corresponding differences from the desired profile of the binary response signal. However, there is also frequently no need to precisely distinguish the nature of the fault since the only interest of the operator of an electrical appliance in which the electromagnetic relay is used is to determine whether the relay operation is correct or faulty. If one of the possible faults occurs, then the operator will replace the appropriate switching group with the relay control and the electromagnetic relay, irrespective of the nature of the fault, in order to ensure that his electrical appliance operates correctly. If precise fault differentiation is nevertheless desirable, then either the binary response signal must be continuously monitored by means of the monitoring device or the number of measurement times must be increased correspondingly by further characteristic times, since this makes it possible to indicate further meaningful differences in the binary response signal. In this case, it is possible for the monitoring device to also emit the nature of the fault, at the same time as its fault message. However, in the case of the discontinuous analysis described with just two measurement times, it is also feasible to at least correspondingly isolate the choice of possible types of fault. For example, during the check with the relay coil 11 in the switched-on state, it is possible during the check of the level according to step 77 (see figure 7) for a more specific fault message to be emitted if a difference is found, indicating that either the second switching device 12b is permanently short-circuited or the first switching device 12a is switched off permanently, or that there is a broken conductor in the relay coil 11. Isolation to a permanently switched-off second switching device 12b is already possible during the check of the level of the binary response signal in step 73, as shown in figure 7. By way of example, fault messages such as these can be helpful for repairing a defective relay assembly, or when searching for a systematic fault cause. WE CLAIM 1. A switching arrangement for operating an electromagnetic relay which has a relay coil (11) and relay contacts, in which two switching devices (12a, 12b) are arranged in a current path (10) with the relay coil such that a first switching device (12a) is connected to a first connection of the relay coil (11) and a second switching device (12b) is connected to a second connection of the relay coil (11); and a control device (13) is provided, which is designed to close both switching devices (12a, 12b) in order to produce a current flow through the relay coil (11) , and to open both switching devices (12a, 12b) in order to interrupt a current flow through the relay coil (11); characterized in that the control device (13) is designed to transmit test signals (P_A, P_B) to the first and the second switching devices (12a, 12b), wherein the test signals (P_A, P_B) are created such that they do not influence the instantaneous state of the relay contacts; a measurement voltage (Umeas) is applied to one input of a conversion device (15) and is tapped off between one connection of the relay coil (11) and one of the switching devices (12a, 12b), wherein the conversion device (15) is designed to convert the measurement voltage (Umeas) to a binary response signal (BS); and a monitoring device (16) is connected to one output of the conversion device (15), evaluates the profile of the binary response signal (BS) during the transmission of the test signals (P_A, P_B) by the control device (13), and indicates a fault in the relay coil (11) or one of the switching devices (12a, 12b) if the profile of the binary response signal (BS) differs from an expected profile. 2. The switching arrangement as claimed in claim 1, characterized in that the two switching devices (12a, 12b) are semiconductor switches, in particular transistors. 3. The circuit arrangement as claimed in claim 1 or 2, characterized in that one connection of in each case one damping capacitor (27a, 27b) is arranged in the current path (10) of the relay coil (11), in each case between one connection of the relay coil (11) and one switching device (12a or 12b). 4. The circuit arrangement as claimed in one of the preceding claims, characterized in that the conversion device (15) has a voltage divider (22) which is arranged in parallel with the current path (10) of the relay coil (11), and to whose voltage divider tap (23) a measurement voltage (Umeas) is on the one hand applied, and on the other hand the voltage divider tap (23) is connected to a control input of a further switching device (24) in order to obtain the binary signal (BS) . 5. The circuit arrangement as claimed in claim 4, characterized in that the further switching device (24) is a semiconductor switch, in particular a MOSFET. 6. A method for operating an electromagnetic relay which has a relay coil (11) and relay contacts, in which two switching devices (12a, 12b) are closed in order to produce a current flow through the relay coil (11), and two switching devices (12a, 12b) are opened in order to interrupt a current flow through the relay coil (11), wherein the switching devices (12a, 12b) are arranged in a current path with the relay coil (11) such that the first switching device (12a) is connected to a first connection of the relay coil (11), and the second switching device (12b) is connected to a second connection of the relay coil (11); characterized in that a control device (13) emits test signals (P_A, P_B) to the two switching devices (12a, 12b), which test signals (P_A, P_B) do not influence the instantaneous state of the relay contacts; a measurement voltage (Umeas) is tapped off between one connection of the relay coil (11) and one of the switching devices (12a, 12b); the measurement voltage (Umeas) is converted to a binary response signal (BS); and a fault in the relay coil (11) or in one of the two switching devices (12a, 12b) is indicated if the profile of the binary response signal (BS) differs from an expected profile. 7. The method as claimed in claim 6, characterized in that test signals (P_A, P_B) which are shorter than a response time of the relay are emitted to the two switching devices (12a, 12b) with a time offset when no current is flowing through the relay coil (11). 8. The method as claimed in claim 7, characterized in that when the measurement voltage (Umeas) is tapped off between the second connection of the relay coil (11) and the second switching device (12b), the test signals (P_A, P_B) are emitted in the following sequence: a) a test signal (P_B) is emitted to the second switching device (12b); b) no test signal is emitted during a signal pause; c) a test signal (P_A) is emitted to the first switching device (12a). 9. The method as claimed in claim 7, characterized in that when the measurement voltage (Umeas) is tapped off between the first connection of the relay coil (11) and the first switching device (12b), the test signals (P_A, P_B) are emitted in the following sequence: a) a test signal (P_A) is emitted to the first switching device (12a). b) no test signal is emitted during a signal pause; c) a test signal (P_B) is emitted to the second switching device (12b); 10. The method as claimed in one of the preceding claims, characterized in that when no current is flowing through the relay coil (11), the first switching device (12a) is operated all the time, while the second switching device (12b) is operated via a pulsed test signal (P_B). 11. The method as claimed in one of the preceding claims, characterized in that in order to determine whether there is a fault in the relay coil (11) or one of the switching devices (12a, 12b), the binary response signal (BS) is compared with the expected profile at at least two characteristic times (for example t1 and t2), wherein at least one change relating to the state of at least one test signal (P_A, P_B) has taken place between the characteristic times (for example tl and t2). 12. The method as claimed in one of the preceding claims, characterized in that the method is repeated at regular time intervals. 13. The method as claimed in one of the preceding claims, characterized in that the control device (13) emits different test signals (P_A, P_B) depending on the state of the relay coil. The invention relates to a switching arrangement for controlling an electromagnetic relay comprising a relay coil (11) and relay contacts, two switching devices (12a, 12b) being arranged in a current path (10) with the relay coil (11). A control device (13) is provided and set up in such a way as to close the two switching devices (12a, 12b) in order to generate a current flow through the relay coil (11), and to open the two switching devices (12a, 12b) in order to interrupt a current flow through the relay coil (11). The aim of the invention is to provide a circuit arrangement and an above-mentioned method. In order to desi gn such a circuit arrangement in such a way that an anticipatory check of the relay coil (11) and the two switching devices (12a, 12b) for errors is enabled, the control device (13) is designed to send test signals (P_A, P_B) to the first and the second switching devices (12a, 12b). A conversion device (l5) is subjected to a measuring voltage (U mess) which is converted into a binary response signal (BS). An error in the relay coil (11) or on of the switching devices (12a, 12b) is displayed when the course of the binary response signal (BS) deviates from an expected course. The invention also relates to a corresponding method for controlling an electro magnetic relay.

Full Text

Description
Switching arrangement and method for operating an
electromagnetic relay
The invention relates to a switching arrangement for operating
an electromagnetic relay which has a relay coil and relay
contacts, in which two switching devices are arranged in a
current path with the relay coil such that a first switching
device is connected to a first connection of the relay coil and
a second switching device is connected to a second connection
of the relay coil; and a control device is provided, which is
designed to close both switching devices in order to produce a
current flow through the relay coil, and to open both switching
devices in order to interrupt a current flow through the relay
coil. The invention relates furthermore to a corresponding
method for operating an electromagnetic relay.
Electromagnetic relays are frequently used in order to carry
out controlled switching operations in electrical appliances.
Electromagnetic relays normally comprise a relay coil and at
least one pair of electrical relay contacts. When an electric
current is applied to the relay coil, then a magnetic field is
produced around the relay coil as a result of which - in the
case of a self-opening relay - the relay contacts are closed,
such that current can flow via the relay contacts. When the
current flowing through the relay coil is interrupted again,
then the moving part of the relay contacts is moved back to its
original position, for example by means of a spring device,
thus opening the relay contacts and interrupting the current
flow via them. In the case of self-closing relays, the contacts
are

closed when no current is flowing through the relay coil, and
they are opened when current is flowing through it.
Electromagnetic relays are normally used where the aim is to
switch a comparatively high current on or off in a switching
circuit, by means of a comparatively low current from a control
circuit. In this case, the electromagnetic relay provides
galvanic decoupling between the control circuit and the
switching circuit.
Electromagnetic relays are used, for example, in electrical
protective devices for monitoring electrical power supply
systems in order to trip an electrical circuit breaker, by
closing the relay contacts of a so-called "command relay", thus
interrupting the fault current, in the event of a fault (for
example a short circuit) in the electrical power supply system.
When electromagnetic relays are used in safety-relevant areas
such as these, it is of very major importance to reliably
prevent inadvertent switching on or off, in order on the one
hand to ensure a high level of safety in the event of a fault,
and on the other hand to avoid costly spurious tripping.
In order to monitor the state of the relay contacts, it is
first of all possible to feed back their actual state, that is
to say whether they are open or closed, to the control device
of the relay coil. If there is a difference between the nominal
state and the actual state of the relay contacts, a fault in
the relay operation is deduced.

However, such monitoring is comparatively complex because, in
this case, the galvanic decoupling achieved by the relay
between the control circuit and the switching circuit must be
exceeded in order to feed back information relating to the
state of the relay contacts. Furthermore, in this case, a fault
can be identified only after it has already occurred, that is
to say the relay contacts have already assumed an undesirable
state. Predictive monitoring is impossible.
Efforts have therefore been made to make the control circuit
for the relay coil as fail-safe as possible. By way of example,
faults in switching devices can occur by melting of the
switching contents as a result of an excessively high switching
power or excessively high temperature, as a result of which the
corresponding switching device is permanently short-circuited.
In the case of semiconductor switches, for example transistors,
a similar effect is known as so-called "breakdown" of the
connections of the semiconductor switch. It is likewise
possible, both in the case of mechanical switching devices and
semiconductor switches, for the switches to permanently block
the current flow because of an internal fault. Furthermore, a
fault can also occur in the relay coil itself, as a result of
which, for example, current can no longer flow through the
relay coil because of a broken line, for example.
In order to design the control circuit to be as fail-safe as
possible, the relay coil is operated not only via a single
switching device, which may be susceptible to faults, but
instead of this via two switching devices located in the
current path of the relay coil. The relay coil is operated only
when both switching devices are closed at the same time. As
soon as one

switching device has opened, the current flow through the
relay coil is interrupted. This

achieves relatively high operating reliability with respect to
inadvertent activation of the relay coil, since a faulty,
permanently short-circuited switching device cannot on its own
undesirably activate the relay coil. By way of example, one
such switching device is known from German patent specification
DE 44 09 287 C1, which discloses a relay coil which has two
switching devices in the form of transistors located in one
current path.
The invention is based on the object of specifying a switching
arrangement and a method of the type mentioned initially, which
allow predictive checking of the relay coil and of both
switching devices for the possible occurrence of faults.
With regard to the switching device, this object is achieved by
a switching arrangement of the type mentioned initially, in
which the control device is designed to transmit test signals
to the first and the second switching devices, wherein the test
signals are created such that they do not influence the
instantaneous state of the relay contacts; a measurement
voltage is applied to one input of a conversion device and is
tapped off between one connection of the relay coil and one of
the switching devices, wherein the conversion device is
designed to convert the measurement voltage to a binary
response signal; and a monitoring device is connected to one
output of the conversion device, evaluates the profile of the
binary response signal during the transmission of the test
signal by the control device, and indicates a fault in the
relay coil or one of the switching devices if the profile of
the binary response signal differs from an expected profile.

The particular advantage of the switching arrangement according
to the invention is that the correct operation of the relay-
coil and of the two switching devices can be checked easily
even before the relay has carried out a faulty switching
operation. This makes it possible to check the relay coil and
the two switching devices for possible faults, so to speak
predictively. In this context, "predictively" therefore means
that the serviceability can be checked without having to carry
out a switching operation of the relay contacts. To do this,
just a single measurement signal in the form of the measurement
voltage is tapped off and monitored, in a comparatively simple
manner. A malfunction of the two switching devices or of the
relay coil can advantageously be achieved as the relay, both in
the switched-on state and in the switched-off state, by
applying test signals to the two switching devices which,
however, do not influence the instantaneous state of the relay
contacts.
If a fault is discovered in one of the switching devices or in
the relay coil during the monitoring, then an operator of an
appliance in which the electromagnetic relay is installed - for
example the operator of a corresponding electrical protective
device - can be informed of this by a fault message relating to
this, as a result of which he can initiate replacement of the
assembly fitted with the relay and its control circuit.
One advantageous embodiment provides that the two switching
devices are semiconductor switches, in particular transistors.
Semiconductor switches such as these can be switched on and off
particularly quickly and with low switching power levels.

Furthermore, a further advantageous embodiment of the switching
arrangement according to the invention provides that one
connection of in each case one damping capacitor is arranged in
the current path of the relay coil, in each case between one
connection of the relay coil and one switching device. The
damping effect of the capacitors allows the profile of the
measurement voltage and therefore the profile of the binary
response signal to be extended in time, so as to allow
particularly simple evaluation.
Furthermore, a further advantageous embodiment of the switch
arrangement according to the invention provides that the
conversion device has a voltage divider which is arranged in
parallel with the current path of the relay coil, and to whose
voltage divider tap a measurement voltage is on the one hand
applied, and on the other hand the measurement voltage is
supplied to an operating input of a further switching device in
order to obtain the binary signal. This allows a binary
response signal to be produced from the measurement voltage,
without a high level of circuit complexity.
By way of example, the further switching device may be a
semiconductor switch, in particular a MOSFET (metal oxide
semiconductor field effect transistor). Field effect
transistors are operated by voltages and are therefore, in the
present case, particularly highly suitable for converting the
measurement voltage to a binary response signal.
With regard to the method, the abovementioned object is
achieved by a method for operating an electromagnetic relay
which has a relay coil and relay contacts, in which two
switching devices are closed in order to produce a current flow
through the relay coil, and two switching devices are opened in
order to interrupt a current flow through the relay coil,

wherein the switching devices are arranged in a current path
with the relay coil such that the first switching device is
connected to a first connection of the relay coil, and the
second switching device is connected to a second connection of
the relay coil, wherein, in the case of the method according to
the invention, the control device emits test signals to the two
switching devices, which test signals do not influence the
instantaneous state of the relay contacts; a measurement
voltage is tapped off between one connection of the relay coil
and one of the switching devices; the measurement voltage is
converted to a binary response signal; and a fault in the relay
coil or in one of the two switching devices is indicated if the
profile of the binary response signal differs from an expected
profile. The described method advantageously allows predictive
checking of the control circuit of the electromagnetic relay.
It is furthermore considered to be an advantageous development
for test signals which are shorter than the response time of
the relay to be emitted to the two switching devices when the
relay contacts are in the open state. In this case, the
response time of the relay is considered to be that time which
a magnetic field produced by the relay coil requires to react
to a sudden change in a voltage applied to the relay coil by a
change in the switching state of the relay contacts.
For example, if the relay coil is switched off when a magnetic
field has been formed completely, then the magnetic field
decays only after a certain time delay. The state of the relay
contacts does not change until the magnetic field strength is
no longer adequate to

hold the relay contacts in their previous position. If the
relay coil is switched on again

in good time, then the magnetic field builds up again, and the
relay contacts remain in their state, without any change.
In the converse situation, a voltage is suddenly applied to the
relay coil, through which no current was previously flowing, a
magnetic field of the relay coil requires a certain time period
before its magnetic field strength is sufficient to operate the
relay contacts. If the current flow is interrupted again in
good time, then the- state of the relay contacts does not
change.
The time duration of the test signals must therefore be created
such that they are sufficiently short to ensure that no change
in the state of the relay contacts occurs, because of the
inertia of the building-up or decaying magnetic field of the
relay coil.
The method according to the invention can be used to check the
two switching devices and the relay coil for possible faults
both when no current is flowing through the relay coil and when
current is flowing through the relay coil.
Specifically, for example, a check is carried out when no
current is flowing through the relay coil and with the
measurement voltage being tapped off between the second
connection of the relay coil and the second switching device,
by test signals being emitted in the following sequence:
a) a test signal is emitted to the second switching
device;
b) no test signal is emitted during a signal pause;

c) a test signal is emitted to the first switching device.

When the measurement voltage is tapped off between the first
connection of the relay coil and the first switching device,
the distribution of the test signals between the switching
devices is correspondingly reversed.
When current is flowing through the relay coil, a check can be
carried out according to one advantageous development by
permanently operating the first switching device, while the
second switching device is operated via a pulsed test signal.
By way of example, the time profile of the binary response
signal can be continuously compared with the expected profile.
However, one particularly advantageous embodiment of the method
according to the invention provides that in order to determine
whether there is a fault in the relay coil or one of the
switching devices, the binary response signal is compared with
the expected profile at at least two characteristic times,
wherein at least one change relating to the state of at least
one signal has taken place between the characteristic times. In
this embodiment, the monitoring device's computation power
which is required for the comparative process is kept
relatively minor, since the profile of the binary response
signal and the expected profile need in the simplest case be
compared with one another at only two particularly
characteristic times, and in consequence there is no need for
continuous comparison. Since a 100% match between the binary
response signal and the expected profile can normally be
achieved only with difficulty in any case, a further advantage
of this embodiment is that, if the times under consideration
are chosen sensibly - specifically sufficiently far away from
those times at which a

change in the test signals occurs - insignificant differences
between the profile of the binary response signal and the
expected profile will not lead to a fault message.
In order to allow the two switching devices and the relay coil
to be monitored continuously for possible faults, the method
according to the invention should be repeated at regular time
intervals.
The control device advantageously emits different test signals,
depending on the state of the relay contacts.
The invention will be explained in more detail in the following
text with reference to exemplary embodiments. In this case:
Figure 1 shows a schematic block diagram of one general
embodiment of a switching arrangement for operating
an electromagnetic relay,
Figure 2 shows a circuit diagram of one possible embodiment of
a switching arrangement for operating an
electromagnetic relay,
Figure 3 shows a plurality of diagrams in order to explain
examples of test signals and the measurement voltages
caused by them, and binary response signals, when the
relay coil is checked without any current flowing
through it,
Figure 4 shows a method flowchart in order to explain one
exemplary embodiment of a check with no current
flowing through the relay coil,

Figure 5 shows a monitoring test signal sequence with no
current flowing through the relay coil,
Figure 6 shows a plurality of diagrams in order to explain
examples of test signals and the measurement voltages
caused by them, and binary response signals when the
relay coil is checked with current flowing through
it, and
Figure 7 shows a method flowchart in order to explain one
exemplary embodiment of a check with current flowing
through the relay coil.
Figure 1 shows a schematic block diagram of one exemplary
embodiment of a switching arrangement for operating an
electromagnetic relay. A control circuit for the
electromagnetic relay comprises a series circuit in a current
path 10 of a relay coil 11 with a first switching device 12a
and a second switching device 12b, with the switching devices
12a and 12b being symbolized, just by way of example, by
mechanical switching devices in figure 1. The switching devices
12a and 12b may be formed by mechanical switches or
semiconductor switches, such as transistors.
A high and a low voltage level are respectively indicated by
"V+" and "V-". By way of example, the high voltage level V+ may
be 10V, while the low voltage level V- is 0V. The first
switching device 12a is connected to a first connection 11a of
the relay coil 11 on the side with the high voltage level, V+,
while the second switching device 12b is connected to a second
connection l1b of the relay coil 11 on the side with the low
voltage level V-.

The control inputs of the first and the second switching
devices 12a and 12b are connected to a control device 13 . The
switching devices 12a and 12b can be switched on and off via
the control device 13. The control device 13 is designed to
emit test signals to the control inputs of the first and second
switching devices 12a and 12b, as will be explained in more
detail later.
A measurement voltage Umeas is tapped off via a branch 14 at the
connection of the second connection 11b of the relay coil 11 to
the second switching device 12b, and is supplied to a
conversion device 15. The conversion device 15 is designed to
convert the measurement voltage Umeas to a binary response
signal BS, and to emit this at its output. The binary response
signal BS is supplied to a monitoring device 16, which can
interchange information with the control device 13 . The
monitoring device 16 may either form an autonomous unit - as
illustrated in figure 1 - or else may be integrated in the
control device 13, - although this is not illustrated in figure
1. Both the control device 13 and the monitoring device 16 may
have a microprocessor or some other logic module (for example
an ASIC) which controls its operation.
Although this is not illustrated in figure 1, the measurement
voltage Umeas can also be arranged at the connection between the
first switching device 12a and the first connection of the
relay coil 11. The sequence of the test signals for monitoring
the current path 10, as described in the following text, should
in a situation such as this be subdivided in a correspondingly
reversed manner between the two

switching devices 12a and 12b, and the fault situations
described below should likewise be appropriately adapted.
However, the following examples are intended to be based on the
measurement voltage Umeas being tapped off as shown in figure 1,
that is to say between the second switching device 12b and the
second connection of the relay coil 11.
In one possible more specific embodiment, a switching
arrangement for operating an electromagnetic relay may be
designed, for example, as shown in figure 2. The same reference
symbols are used in figure 2 for components corresponding to
figure 1.
Figure 2 shows a relay coil 11 whose first connection 11a on
the side with the high voltage level V+ is connected to a first
switching device 12a, while the second connection 11b of the
relay coil 11 on the side with the low voltage level V- is
connected to a second switching device 12b.
By way of example, the switching devices 12a and 12b are
illustrated in figure 2 as semiconductor switches in the form
of transistors.
A dashed-line boundary indicates a group of switching elements
corresponding to the conversion device 15 shown in figure 1.
The core piece of the conversion device 15 in the embodiment
shown in figure 2 is formed by a voltage divider 22 which, for
example, comprises two non-reactive resistors 22a and 22b. A
voltage divider tap 23 is located between the two non-reactive
resistors 22a and 22b and is connected on the one hand to the
branch 14 for the measurement voltage, and

on the other hand to a control input of a further switching
device 24.
A series circuit 25 is arranged in parallel with the relay coil
11 and the switching device 12a, is composed of a non-reactive
resistor 25a and a diode 25b, and is used to cope with
overvoltages which can occur when the current flow through the
relay coil 11 is interrupted. A further non-reactive resistor
26 is used to set the voltage level of the binary response
signal BS.
One connection of a first damping capacitor 27a is connected to
the first connection 11a of the relay coil 11 at the connection
of the first switching device 12a, and its other connection is
at the low voltage level V-. A second damping capacitor 27b is
connected in a corresponding manner by its first connection to
the connection between the second switching device 12b and the
second connection 11b of the relay coil 11, and its second
connection is likewise at the low voltage level V-.
The method of operation of the switching arrangement
illustrated in figure 2 will be explained in more detail in the
following text, in particular with reference to the checking of
the two switching devices 12a and 12b and of the relay coil 11
for possible faults. Reference will also be made to figures 3
to 7, in addition to figure 2, for this purpose.
The control device 13 is first of all used to produce a current
flow through the relay coil 1, or to interrupt it, by
simultaneously opening or respectively closing the switching
devices 12a and 12b. Simultaneously closing the two switching
devices 12a and 12b results in a current flow through the relay
coil 11, as a result of which a

corresponding magnetic field is developed in the relay coil 11
and, beyond a certain magnetic field strength, results in a
change in the state of the relay contacts (not illustrated) of
the electromagnetic relay. In order to interrupt the current
flow in the relay coil, the control device 13 opens the two
switching devices 12a and 12b, as a result of which the
magnetic field produced by the relay coil 11 decays again. When
the field strength produced by the magnetic field is no longer
sufficient to keep the relay contacts in their position, they
change over to their normal position - for example by the
influence of spring force.
In the situation when a fault is present in one of the two
switching devices 12a and 12b or the relay coil 11, it is no
longer possible to ensure correct operation of the relay coil
11 and therefore of the switching circuit arranged at the relay
contacts. For the situation in the example, in which the
electromagnetic relay is a command relay for operating an
electrical circuit breaker, a malfunction such as this can, for
example, cause undesirable spurious tripping of the circuit
breaker, or intended tripping of the circuit breaker may be
prevented. The current path 10 comprising the two switching
devices 12a and 12b of the relay coil is checked for this
reason. Irrespective of whether or not current is flowing
through the relay coil 11, the control device 13 emits
different test signals P_A, P_B to the switching devices 12a
and 12b, resulting in a change in the voltage level at the
branch 14.
The measurement voltage Umeas that is present at this branch 14
is supplied to the conversion device 15, where it is converted
to a binary

response signal BS. The profile of the binary response signal
BS is compared by the monitoring device 16 with an expected
profile, and a fault in the current path 10 is identified if
the expected profile and the actual profile of the binary
response signal BS differ from one another. In order to allow
the expected profile and the actual profile of the binary
response signal BS to be compared with one another, the
monitoring device 16 is able to interchange information with
the control device 13 in order, for example, to be informed of
the start of the sending of the test signals P_A, P_B to the
two switching devices 12a and 12b.
When the monitoring device 16 identifies a fault in the current
path 10, an appropriate fault message can be emitted which
informs an operator of an appliance in which the
electromagnetic relay is installed of the fault. The operator
of the appropriate appliance can then replace the corresponding
faulty assembly even before the electromagnetic relay can
actually malfunction.
A check of the current path 10 for possible faults can be
carried out with or without current flowing through the relay
coil, and correspondingly with the relay contacts switched off
or switched on, without having to influence the state of the
relay contacts in the process.
Figures 2, 3 and 4 will first of all be used to explain in the
following text how the current path 10 is checked when
(deliberately) no current is flowing through the relay coil.
For this purpose, the two upper diagrams in figure 3 show the
profiles of the test signals P_A and P_B, while the

following ten diagrams, in each case on the left-hand side,
show the measurement voltages which are present at the branch
14 when no faults are present and for various fault situations,
while the right-hand side in each case shows the binary
response signals, which result from the respective measurement
voltages, when no fault is present and for various fault
situations.
As can be seen from figure 3, a test signal P_B is first of all
supplied to the second switching device, in order to start a
test process. This test signal P_B switches the second
switching device 12B to its closed state.
In this case, the duration of the test signal P_B is chosen
such that, even in the situation in which the first switching
device 12a has been permanently short-circuited because of a
fault, the duration of a current flow which then results
through the relay coil 11 has no effect on the state of the
relay contacts. The duration of the test signal P_B must
therefore be less than the response time, as already explained
earlier, of the relay. Normally, the duration of a test signal
is for this purpose chosen to be between a lower and an upper
limit, with the lower limit indicating that time which is
required to generate a correct binary response signal in the
conversion device 15, and the upper limit allowing an
adequately safe margin from the response time of the relay. By
way of example, the possible range for the time duration of the
test signals are between approximately 40 and approximately
200 us.
As can be seen from figure 3, the emission of the test signal
P_B to the second switching device 12b is ended again after a
short time period chosen in this way, and this is followed by a
signal pause, during which no test signal is emitted to the
switching

devices 12a or 12b. The switching pause is followed by a
further test signal P_A to be emitted to the first switching
device 12a, causing the switching device 12a to close. The time
duration of the test signal P_A must also be chosen to be
sufficiently short that the state of the relay contacts is not
influenced even if the second switching device 12b is in a
permanently short-circuited state because of the fault. The
time duration of the test signal P_A must therefore also be
shorter than the response time of the relay.
The test process is ended after the end of this test signal
sequence; a further test process can be started after a pause
of any defined length. For example, it is possible for another
test process to be initiated every 250 us.
The diagrams arranged in the second line of figure 3 show the
profile of the measurement voltage in the situation when
both the switching devices 12a and 12b and the relay coil 11
are in a correct, that is to say fault-free, state (corr =
correct). The profile of the measurement voltage will now
be explained with reference to figure 2. This is based on the
assumption that the two switching devices 12a and 12b are
operating correctly and they are both first of all in the
switched-off state.
Initially, the measurement voltage is at a mid-voltage
level, which is predetermined by the voltage divider 22. The
binary response signal is at a high level, since the
measurement voltage is sufficient to switch on the
further switching device 24. The emission

of the test signal P_B to the second switching device 12b
closes the switching device 12b, and the measurement voltage
at the branch 14 is drawn to the low voltage level V-,
since the second switching device 12b bridges the lower
resistor 22b in the voltage divider 22. The profile of the
measurement voltage in figure 3 thus exhibits a sudden
fall, as soon as the test signal P_B closes the switching
device 12b. In a corresponding manner, the binary response
signal BScorr falls to a low level, since the further switching
device is switched off because of the low measurement voltage
applied to it. When the test signal P_B ends, the second
switching device 12b returns to the switched-off state, and the
previously discharged damping capacitors 27a and 27b are
charged via the upper resistor 22a in the voltage divider 22.
If the damping capacitors 27a and 27b and the non-reactive
resistor 22a in the voltage divider are of adequate size, this
charging process takes place sufficiently slowly but virtually
no rise in the measurement voltage is perceptible toward
the signal pause. The rise in the measurement voltage is
at least not sufficient to change the further switching device
24 in the conversion device 15 to its state in which current is
passed through, as a result of which the binary response signal
BScorr still remains at the low level during the signal pause.
When the test signal P_A acts on the first switching device 12a
after the signal pause, and this switching device 12a is
switched to its state in which current passes through it, the
damper capacitors 27a and 27b are charged comparatively
quickly, since the upper resistor 22a in the voltage divider 22
is bridged, and the high voltage level V+ is applied directly
to the damping capacitors 27a and 27b. This rapid charging
process can also be seen from the

profile of the measurement voltage which rises rapidly
while the second measurement signal P_A is being emitted.
Finally, the measurement voltage is at the high voltage
level V+. As soon as the measurement voltage has reached
a level which causes the further switching device 24 to switch
on, the binary response signal rises suddenly to its high
level. When the emission of the first test signal P_A ends
after the appropriate time period has elapsed, the mid-voltage
level, which is predetermined by the voltage divider 22, is
assumed again at the branch 14, after the damping capacitors
27a and 27b have discharged via the lower resistor 22b in the
voltage divider 22.
As already explained in conjunction with figure 2, the binary
response signal is transmitted to the monitoring device 16,
which compares the profile of the binary response signal with
an expected profile. A comparison such as this can be carried
out either continuously throughout the entire test process, or
can be carried out discontinuously only at specific
characteristic times in order on the one hand to save
computation capacity in the monitoring device and on the other
hand to be insensitive to insignificant differences between the
binary response signal and the expected profile, which would
not indicate a fault in the current path 10.
For this purpose, figure 3 shows two monitoring times t1 and
t2, which are each indicated by circles in the profile of the
binary response signals. In consequence, for the correct
profile of the binary response signal, the signal level must be
low at the measurement time t1, and must be high at the
measurement time t2. If the monitoring device 16 identifies the
correct profile on the basis of the signal levels measured at
these times, then it deduces that

there are no faults in the current path 10, and does not carry-
out any further actions, until the next test process is
initiated.
The profiles of the respective measurement voltages and of the
binary response signals which result from them will be
discussed in the following text for fault situations in which
one of the two switching devices 12a or 12b is permanently
short-circuited or permanently switched off, or there is a
broken line in the relay coil 11.
First of all, the fault situation F1 will be considered, in
which the second switching device 12b is permanently switched
off because of a fault. In this situation, the emission of a
test signal P_B to the second switching device 12b has no
effect whatsoever since the permanently switched off switching
device 12b cannot be changed to the switched-on state in this
way. In consequence, the corresponding measurement voltage
remains at the mid-voltage level set by the voltage
divider 22 and it does not fall, as expected according to the
profile of the correct measurement voltage indicated by a
dashed line, to the low voltage level V-. Correspondingly, the
binary response signal BSF1 remains at its high level. During
the signal pause, no test signal is emitted to the switching
devices 12a or 12b, as a result of which the measurement
voltage and the resultant binary response signal BSF1
correspondingly do not change. The emission of the test signal
P_A to the first switching device 12a switches it to its
switched-on state - since it is operating correctly - as a
result of which the measurement voltage which is present at the
branch 14 rises to the high voltage level V+ after charging of
the damping capacitors 27a and 27b. However, this increase in
the measurement voltage to the high voltage level V+

has no effect on the profile of the binary response signal
BSF1, because the binary response signal BSF1 is already at its
high level. After the end of the test signal P_A, the first
switching device 12a is switched off again and the damping
capacitors 27a and 27b are discharged to the mid-voltage level
which is predetermined by the voltage divider 22. In
consequence, the monitoring device 16 detects a binary response
signal BSF1 which is permanently at the high level throughout
the test process. In the case of a discontinuous analysis of
the times t1 and t2, the monitoring device 16 identifies a
difference between the binary response signal BSF1 and the
expected profile (indicated by a dashed line) at the time t1,
since the binary response signal BSF1 is at a high level and is
not, as expected, at a low level. From this, the monitoring
device 16 deduces that there is a fault in the current path 10,
and emits a fault signal in order to warn the operator of an
electrical appliance containing the electromagnetic relay.
The fault situation F2 will be considered next, in which the
second switching device 12b is permanently short-circuited, as
a result of which current can flow continuously via the
switching device 12b. The measurement voltage which is
present at the branch 14 in this situation is already at the
low level voltage V- before the start of the test process,
because of the short-circuited switching device 12b. Switching
on the test signal P_B has no influence on this, since the
switching device is in the open state in any case. The
resultant binary response signal BSF2 is in consequence
permanently at its low level before the start of the test
process and while the test signal P_B is being emitted. During
the signal pause, the state of both the measurement voltage

that of the binary response signal BSF2 do not change,
since the short-circuited switching device 12b keeps the branch
14 permanently at the low voltage level V-. The emission of the
test signal P_A to the first switching device 12a changes
nothing relating to this, either; the branch 14 remains
permanently at the low voltage level V- as a result of the
short-circuited switching device 12b, even when the switching
device 12a is closed. This fault situation F2 illustrates the
importance of the time duration of the test signals since, if
the test signal P_A were chosen to be too long, the response
time of the relay would be exceeded if the switching device 12b
were to be permanently short-circuited, and the state of the
relay contacts would therefore change undesirably. Emitting the
test signal P_A for a correspondingly short time is the only
way to ensure that, although on the one hand it is possible to
detect the binary signals BSF2, the response time of the relay
is, on the other hand, not exceeded, so that the state of the
relay contacts does not change. In this fault situation F2, the
monitoring device 16 is supplied with a binary response signal
BSF2 which is permanently at the low level. If the binary
response signal BE?1 is analyzed discretely at the times t1 and
t2, a difference will be found at the time t2, where the binary
response signal BSF2 is at the low level, instead of at the
expected high level. The monitoring device 16 therefore emits a
fault signal in order to indicate a fault in the current
path 10.
The next fault situation F3 comprises both faults, in which the
switching device 12a is switched off permanently and there is a
broken line in the relay coil 11 (or both) , such that no
current can flow via the relay coil 11. In this case, the
measurement voltage starts at the

mid-voltage potential, which is predetermined by the voltage
divider 22, and, on emission of the test signal P_B, falls to
the low voltage level because the second switching device 12b
is then short-circuited. In a corresponding manner, the binary
response signal BSF3 falls to its low level. During the signal
pause, the damping capacitor 27b (in the event of a broken line
in the relay coil 11) or both damping capacitors 27a and 27b
(if the first switching device 12a is permanently switched off)
is or are charged again via the upper resistor 22a in the
voltage divider 22, with this charging process taking place
sufficiently slowly, as already mentioned, that the state of
the further switching device 24 does not change. In
consequence, the binary response signal BSF3 remains at the low
level. Since, in the fault situation F3 under consideration
here, either the first switching device 12a or the relay coil
11 (or both) 'are or is switched off permanently, the emission
of a test signal P_A to the first switching device 12a cannot
produce any current flow through the switching device 12a and
the relay coil 11, as a result of which the process of charging
the damping capacitors 27a and 27b via the resistor 22a
continues correspondingly slowly, as a result of which the
measurement voltage which is present at the branch 14 is
also not sufficient to switch on the further switching device
24 while the test signal P_A is being emitted. In consequence,
the binary response signal BSF3 remains at the low level. The
monitoring device 16 is supplied with a low level of the binary
response signal BSF3 at each of the times t1 and t2, as a result
of which a difference from the expected profile is found at the
time t2, and a fault signal is emitted.
Finally, the fault situation F4 will be considered, in which
the first switching device 12a is permanently short-circuited.

Since, in this case, the upper resistor 22a in the voltage
divider 22 is permanently bridged, the measurement voltage
in this case starts at the high voltage level V+ even
before the start of the test process. The binary response
signal BSF4 is correspondingly at the high level. Emission of
the test signal P_B closes the second switching device 12b, and
the voltage level at the branch 14 therefore falls to the low
voltage level V-. This sudden change can be seen from the
profile of the measurement voltage and also from the
binary response signal BSF4 which results from this. After the
end of the test signal P_B, the second switching device 12b
once again is switched off, as a result of which the capacitors
27a and 27b are charged very quickly to the high voltage level
V+ via the permanently short-circuited switching device 12a. In
consequence, the binary response signal BSF4 jumps to the high
level again even during the signal pause. In consequence,
emission of the test signal P_A to the first switching device
12a has no more effect whatsoever on the measurement voltage
and on the binary response signal BSF4 resulting from
this, since the first switching device 12a is permanently
short-circuited in any case, and the branch 14 is already at
the high voltage level V+. In consequence, in this fault
situation, the monitoring device 16 is supplied with the
profile of the binary response signal BSF4 as illustrated in
figure 3. Even when the times t1 and t2 are considered
discretely, the monitoring device 16 identifies a difference
between the binary response signal BEF4 and the expected
profile at the time t1, and emits a fault signal.
Figure 4 illustrates the timing of the test process for
discontinuous testing at the times t1 and t4,

once again in a summarized form on the basis of a method
flowchart. After the start of the test process ("TEST Start"),
the test signal P_B is first of all emitted to the second
switching device 12b by the control device 13, in step 40. A
wait from a specific time period, for example 40 us, takes
place according to step 41, before the second test signal P_B
is switched off again in step 42. A wait for a predetermined
time period, for example 40 us again, once again takes place
during the signal pause in step 43, during which no test signal
is emitted. Once this time period has elapsed, a check is
carried out in step 44 to determined whether the binary
response signal is at the expected low level (annotated "0" in
figure 4). If this is not the case, a fault message is emitted.
However, if the check in step 44 shows that the binary response
signal is at the expected low level, then the test signal P_A
is switched on according to step 45, in order to switch on the
switching device 12a. The test signal P_A is maintained in step
46 for a predetermined time period, for example of 40 us again,
before the monitoring device 16 checks, in step 47, whether the
binary response signal is at the expected high level (the high
level is annotated "1" by way of example, in figure 4). If a
binary response signal difference is found, a fault message is
once again emitted. If a correct binary response signal is
identified, then the test signal P_A is switched off in a next
step 48, and the test process is successfully completed ("TEST
OK") .
After a predetermined time period has elapsed, the test process
can be initiated once again by activating the sequence "TEST
Start", in order to ensure continuous testing of the current
path 10.

The monitoring of the current path 10 for the situation in
which (deliberately) current is flowing through the relay coil
11 will now be described with reference to figures 5 to 7. In
this case as well, there is once again a requirement for the
check to have no influence whatsoever on the state of the relay
contacts.
The switching-on and holding process of the electromagnetic
relay is illustrated first of all in figure 5. As is known, a
relay coil requires more power to be supplied to it in order to
operate the relay contacts, for example while the relay
contacts are being switched on, and is required to hold the
relay contacts in their operated position. In consequence, the
two switching devices 12a and 12b are first of all switched on
at the same time at the time to, in order to move the relay
contacts. The simultaneous operation of both switching devices
12a and 12b ensures a permanently high current flow through the
relay coil 11, as a result of which the contacts can be quickly
moved to their activated position. This activation phase of the
relay contacts lasts, as shown in figure 5, from the starting
time to to the time t*, at which the relay contacts have been
moved to their activated state.
A so-called pulse-width-modulated holding current can then be
passed through the relay coil 11 by pulsed operation of the
second switching device 12b, producing less power, averaged
over time (and therefore also less power loss in the relay
coil), and which is adequate to hold the relay contacts in
their activated state. Once again, in this case as well, the
inertia of the electromagnetic relay is used since - as already
described above - the magnetic field in the relay coil 11 does
not decay until after a certain response time to such an extent
that the relay contacts would once again change to their
deactivated state, such that this response time

is always undershot, and the relay contacts remain permanently
in their activated state, if the pulses are appropriately
short.
This procedure of providing a lower holding current overall for
the electromagnetic relay by a pulse-width-modulated current
flow in the relay coil 11, is already known per se.
The operation of the second switching device 12b, which is
pulsed in any case, is now advantageously also used as the
pulsed test signal P_B for monitoring the corresponding
measurement voltage Umeas at the branch 14, in order to monitor
the current path 10. For explanatory purposes relating to this,
each of the two upper diagrams in figure 6 shows the profile of
the test signals P_A and P_B while the test signal P_B is being
pulsed, and this is emphasized by a border in figure 5. In this
case, the test signal P_A is emitted continuously, while the
test signal P_B is emitted in a pulsed form.
The correct profile of the measurement voltage and the
correct profile of the binary response signal BScorr* resulting
from this are illustrated in the second line of the two
diagrams in figure 6. The profile of the measurement voltage
and the binary response signal BScorr* will be explained
with reference to figure 2.
For the situation in which both the two switching devices 12a
and 12b as well as the relay coil 11 are fault-free, the
switching device 12a is in its closed state at the start of the
test sequence, while the switching device 12b is switched off,
because there is no test signal P_B. In consequence, the high
voltage level V+ is produced at the branch 14, which is
produced by switching on the further switching device 24,

and the binary response signal BScorr is in consequence at the
high level. When the test signal P_B is emitted, the switching
device 12b, which is then closed, draws the measurement voltage
the branch 14 to the lower voltage level V-, since in
this case the lower resistor 22b in the voltage divider 22 is
bridged. Both the measurement voltage and the binary
response signal BScorr* which results from it correspondingly
fall suddenly. As long as the test signal P_B is emitted, the
measurement voltage remains at the low voltage level V-, and
the binary response signal BScorr remains at the low level.
When the test signal p_B ends, the second switching device 12b
is switched off again. The sudden interruption in the current
flow in the relay coil 11 and the magnetic field decay
resulting from this induce an overvoltage, which decays slowly
via the current flowing through the resistor 25a and the diode
25b. The measurement voltage tapped off at the branch 14
correspondingly first of all rises above the high voltage level
V+, and then falls gradually to the high voltage level V+
again. Before the current were to fall below the holding
current again, with the magnetic field strength therefore no
longer being adequate to hold the relay contacts in their
activated position, the test signal P_B must be switched on
again, in order to close the current path 10 again.
The measurement voltage illustrated in figure 6 in
consequence results in a binary response signal BScorr* which,
after the end of the emission of the test signal P_B, once
again changes to its high level again, because the measurement
voltage then rises.

The monitoring device 16 is supplied with the profile of the
binary response signal BS. As when no current is flowing
through the relay coil, the correct profile of the binary
response signal can be tested continuously or discontinuously.
Figure 6 shows two characteristic times t3 and t4 for the
discontinuous analysis, at which the monitoring device 16
checks the profile of the binary response signal. If the
profile of the binary response signal is correct, corresponding
to BScorr*, a low level must in consequence be identified at the
time t3, and a high level at the time t4.
The fault situations which can possibly be identified,
specifically a permanently short-circuited or a permanently
switched-off switching device 12b, a permanently switched-off
switching device 12a or a broken line in the relay coil 11,
will now be explained in the following text.
Since the switching device 12a is in any case permanently held
in its closed state by the emission of a continuous test signal
P_A, the test sequence when current is flowing through the
relay coil 11 cannot identify the state in which the first
switching device 12a is permanently short-circuited as a result
of a fault. However, since this would not initially lead to any
malfunction of the electromagnetic relay - the first switching
device 12a should be permanently short-circuited in any case -
the lack of capability to identify a fault such as this is not
a disadvantage of the test process. It will be simple to
identify a fault such as this during the check, as already
described above, when no current is flowing through the relay
coil.

The fault situation F5 will be dealt with first of all, in
which the second switching device 12b is in a permanently
switched-off state. In a situation such as this, the branch 14
would remain permanently at the high voltage level V+ because
of the deliberately short-circuited switching device 12a. Since
emission of the test signal P_B has no influence on the
switching state of the second switching device 12b, because
this second switching device 12b is permanently switched off
because of the fault, the measurement voltage at the
branch 14 remains at the high voltage level V+ irrespective of
the state of the test signal P_B. The binary response signal
BSF5 which results from this in consequence remains
continuously at the high level, as a result of which the
monitoring device 16 finds a difference between the profile of
the binary response signal BSF5 and the expected profile. In
the case of the discontinuous analysis at the times t3 and t4,
the monitoring device 16 finds a difference in the binary
response signal BSF5 at the time t3, with the response signal
being at the high level rather than the low level, and can
generate a fault signal.
The fault situation F6 will be dealt with next, in which the
second switching device 12b is permanently short-circuited. In
this case, the measurement voltage at the branch 14 is
continuously at the low voltage level V- because the switching
device 12b is permanently short-circuited, thus resulting in
the profile of the measurement voltage as shown in figure
6. In this case, the measurement voltage is at the low
voltage level V- irrespective of the test signal P_B, as a
result of which the resultant binary response signal BSF6 also
remains permanently at the low level. The monitoring device 16
can in consequence detect a difference from the expected
profile both in continuous monitoring and discontinuous
monitoring of the profile of the binary

response signal; in the case of discontinuous analysis, the
monitoring device 16 identifies a low level of the binary
response signal BSF6 instead of an expected high level at the
time t4, as a result of which a fault signal can be emitted.
Finally, the fault situation F7 will be considered, in which
either the relay coil 11 has a broken line or the first
switching device 12a is switched off permanently. In this case,
the measurement voltage at the branch 14 first of all
starts at a mid-voltage level, which is set via the voltage
divider 22, since the second switching device 12b also prevents
current from flowing. The binary response signal BSF7 in
consequence starts at the high level. After the test signal P_B
has been switched on, and the second switching device 12b has
in consequence between closed, the measurement voltage
the branch 14 is drawn to the low voltage level V-. This also
results in the binary response signal BSF7 falling to the low
level. The measurement voltage remains at the low voltage
level V-, for as long as the test signal P_B holds the second
switching device 12b in the closed state. After the end of the
test signal P_B, the damping capacitor 27b (in the event of a
broken line in the relay coil 11) or both damping capacitors
(in the event of the first switching device 12a being switched
off permanently) is or are once again charged to the mid-
voltage level through the upper resistor 22a in the voltage
divider 22.
However, once again, this takes place correspondingly slowly,
as a result of which the binary response signal BSF7 initially
remains at the low level. The monitoring device 16 therefore
identifies a

difference between the binary response signal BSF7 and the
expected profile. In discontinuous analysis, the monitoring
device 16 identifies a low level instead of an expected high
level of the binary response signal at the time t4, and can
emit a fault signal.
Finally, figure 7 shows the procedure for the test process when
current is flowing through the relay coil 11, for discontinuous
monitoring of the binary response signal at the times t3 and
t4. After initiation of the test process ("TEST Start"), the
test signal P_B is switched on in a first step 71. After
waiting for a short time period to pass in step 72, a check is
carried out in step 73 to determine whether the binary response
signal BS has assumed a low level ("0") .
The time period required in step 72 may be chosen only to be
sufficiently long that the reaction of the binary response
signal BS to the second switching device 12b being switched on
by the test signal P_B can be detected correctly.
A fault message is emitted if a difference is found between the
binary response signal BS and the expected low level at the
time t3 in step 73. However, if the binary response signal BS
in step 73 corresponds to the expected profile, then, after a
time period which is sufficient to produce the required holding
current has elapsed in step 74, the test signal P_B is switched
off again in step 75, and waiting takes place for a further
short time period in step 76, which time period is chosen such
that a reaction of the binary response signal can be detected.
A check is carried out in step 77 to determine whether the
binary response signal BS is at the expected high level. If
this is not the case, a fault is once again emitted.

However, if the binary response signal is at the expected high
level, then the test process is successfully ended, and can be
started once again after a predetermined time period has
elapsed.
The information interchange that this makes possible between
the control device 13 and the monitoring device 16 makes it
possible for the monitoring device 16 to include the expected
profile of the binary response signal, as appropriate for the
respective nominal state of the relay coil 11 (either with or
without current flowing through it) in its check.
Finally, it should also be mentioned that, in the case of
discontinuous checking each of two characteristic measurement
times, accurate fault differentiation is not possible all the
time, depending on the nature of the fault that has occurred,
since a plurality of fault types at the characteristic times
generally indicate mutually corresponding differences from the
desired profile of the binary response signal. However, there
is also frequently no need to precisely distinguish the nature
of the fault since the only interest of the operator of an
electrical appliance in which the electromagnetic relay is used
is to determine whether the relay operation is correct or
faulty. If one of the possible faults occurs, then the operator
will replace the appropriate switching group with the relay
control and the electromagnetic relay, irrespective of the
nature of the fault, in order to ensure that his electrical
appliance operates correctly.
If precise fault differentiation is nevertheless desirable,
then either the binary response signal must be continuously
monitored by means of the monitoring device or the number of
measurement times must be increased correspondingly by further
characteristic times,

since this makes it possible to indicate further meaningful
differences in the binary response signal. In this case, it is
possible for the monitoring device to also emit the nature of
the fault, at the same time as its fault message.
However, in the case of the discontinuous analysis described
with just two measurement times, it is also feasible to at
least correspondingly isolate the choice of possible types of
fault. For example, during the check with the relay coil 11 in
the switched-on state, it is possible during the check of the
level according to step 77 (see figure 7) for a more specific
fault message to be emitted if a difference is found,
indicating that either the second switching device 12b is
permanently short-circuited or the first switching device 12a
is switched off permanently, or that there is a broken
conductor in the relay coil 11. Isolation to a permanently
switched-off second switching device 12b is already possible
during the check of the level of the binary response signal in
step 73, as shown in figure 7. By way of example, fault
messages such as these can be helpful for repairing a defective
relay assembly, or when searching for a systematic fault cause.

WE CLAIM
1. A switching arrangement for operating an electromagnetic
relay which has a relay coil (11) and relay contacts,
in which
two switching devices (12a, 12b) are arranged in a current
path (10) with the relay coil such that a first switching
device (12a) is connected to a first connection of the relay
coil (11) and a second switching device (12b) is connected to a
second connection of the relay coil (11); and
a control device (13) is provided, which is designed to
close both switching devices (12a, 12b) in order to produce a
current flow through the relay coil (11) , and to open both
switching devices (12a, 12b) in order to interrupt a current
flow through the relay coil (11); characterized in that
the control device (13) is designed to transmit test
signals (P_A, P_B) to the first and the second switching
devices (12a, 12b), wherein the test signals (P_A, P_B) are
created such that they do not influence the instantaneous state
of the relay contacts;
a measurement voltage (Umeas) is applied to one input of a
conversion device (15) and is tapped off between one connection
of the relay coil (11) and one of the switching devices (12a,
12b), wherein the conversion device (15) is designed to convert
the measurement voltage (Umeas) to a binary response signal
(BS); and
a monitoring device (16) is connected to one output of the
conversion device (15), evaluates the

profile of the binary response signal (BS) during the
transmission of the test signals (P_A, P_B) by the control
device (13), and indicates a fault in the relay coil (11) or
one of the switching devices (12a, 12b) if the profile of the
binary response signal (BS) differs from an expected profile.
2. The switching arrangement as claimed in claim 1,
characterized in that
the two switching devices (12a, 12b) are semiconductor
switches, in particular transistors.
3. The circuit arrangement as claimed in claim 1 or 2,
characterized in that
one connection of in each case one damping capacitor (27a,
27b) is arranged in the current path (10) of the relay coil
(11), in each case between one connection of the relay coil
(11) and one switching device (12a or 12b).
4. The circuit arrangement as claimed in one of the preceding
claims, characterized in that
the conversion device (15) has a voltage divider (22)
which is arranged in parallel with the current path (10) of the
relay coil (11), and to whose voltage divider tap (23) a
measurement voltage (Umeas) is on the one hand applied, and on
the other hand the voltage divider tap (23) is connected to a
control input of a further switching device (24) in order to
obtain the binary signal (BS) .
5. The circuit arrangement as claimed in claim 4,
characterized in that
the further switching device (24) is a semiconductor
switch, in particular a MOSFET.

6. A method for operating an electromagnetic relay which has
a relay coil (11) and relay contacts, in which two switching
devices (12a, 12b) are closed in order to produce a current
flow through the relay coil (11), and two switching devices
(12a, 12b) are opened in order to interrupt a current flow
through the relay coil (11), wherein the switching devices
(12a, 12b) are arranged in a current path with the relay coil
(11) such that the first switching device (12a) is connected to
a first connection of the relay coil (11), and the second
switching device (12b) is connected to a second connection of
the relay coil (11); characterized in that
a control device (13) emits test signals (P_A, P_B) to the
two switching devices (12a, 12b), which test signals (P_A, P_B)
do not influence the instantaneous state of the relay contacts;
a measurement voltage (Umeas) is tapped off between one
connection of the relay coil (11) and one of the switching
devices (12a, 12b);
the measurement voltage (Umeas) is converted to a binary
response signal (BS); and
a fault in the relay coil (11) or in one of the two
switching devices (12a, 12b) is indicated if the profile of the
binary response signal (BS) differs from an expected profile.
7. The method as claimed in claim 6, characterized in that
test signals (P_A, P_B) which are shorter than a response
time of the relay are emitted to the two switching devices
(12a, 12b) with a time offset when no current is flowing
through the relay coil (11).

8. The method as claimed in claim 7, characterized in that
when the measurement voltage (Umeas) is tapped off between
the second connection of the relay coil (11) and the second
switching device (12b), the test signals (P_A, P_B) are emitted
in the following sequence:
a) a test signal (P_B) is emitted to the second switching
device (12b);
b) no test signal is emitted during a signal pause;
c) a test signal (P_A) is emitted to the first switching
device (12a).
9. The method as claimed in claim 7, characterized in that
when the measurement voltage (Umeas) is tapped off between
the first connection of the relay coil (11) and the first
switching device (12b), the test signals (P_A, P_B) are emitted
in the following sequence:
a) a test signal (P_A) is emitted to the first switching
device (12a).
b) no test signal is emitted during a signal pause;
c) a test signal (P_B) is emitted to the second switching
device (12b);
10. The method as claimed in one of the preceding claims,
characterized in that
when no current is flowing through the relay coil (11),
the first switching device (12a) is operated all the time,
while the second switching device (12b) is operated via a
pulsed test signal (P_B).

11. The method as claimed in one of the preceding claims,
characterized in that
in order to determine whether there is a fault in the
relay coil (11) or one of the switching devices (12a, 12b), the
binary response signal (BS) is compared with the expected
profile at at least two characteristic times (for example t1
and t2), wherein at least one change relating to the state of
at least one test signal (P_A, P_B) has taken place between the
characteristic times (for example tl and t2).
12. The method as claimed in one of the preceding claims,
characterized in that
the method is repeated at regular time intervals.
13. The method as claimed in one of the preceding claims,
characterized in that the control device (13) emits different
test signals (P_A, P_B) depending on the state of the relay
coil.

The invention relates to a switching arrangement for
controlling an electromagnetic relay comprising a relay
coil (11) and relay contacts, two switching devices (12a,
12b) being arranged in a current path (10) with the relay
coil (11). A control device (13) is provided and set up
in such a way as to close the two switching devices (12a,
12b) in order to generate a current flow through the relay
coil (11), and to open the two switching devices (12a,
12b) in order to interrupt a current flow through the relay
coil (11). The aim of the invention is to provide a circuit
arrangement and an above-mentioned method. In order to desi
gn such a circuit arrangement in such a way that an
anticipatory check of the relay coil (11) and the two
switching devices (12a, 12b) for errors is enabled, the
control device (13) is designed to send test signals (P_A,
P_B) to the first and the second switching devices (12a,
12b). A conversion device (l5) is subjected to a measuring
voltage (U mess) which is converted into a binary
response signal (BS). An error in the relay coil (11) or on
of the switching devices (12a, 12b) is displayed when
the course of the binary response signal (BS) deviates from
an expected course. The invention also relates to a
corresponding method for controlling an electro
magnetic relay.

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Patent Number

271896

Indian Patent Application Number

1616/KOLNP/2010

PG Journal Number

11/2016

Publication Date

11-Mar-2016

Grant Date

09-Mar-2016

Date of Filing

06-May-2010

Name of Patentee

SIEMENS AKTIENGESELLSCHAFT

Applicant Address

WITTELSBACHERPLATZ 2, 80333 MUNCHEN, GERMANY

Inventors:

#	Inventor's Name	Inventor's Address
1	HARALD KAPP	NESTORSTRASSE 33, 10709 BERLIN
2	HARLD STROHMAIER	FICHTESTR. 1B, 14612 FALKENSEE GERMANY

PCT International Classification Number

H01H 47/00

PCT International Application Number

PCT/EP2007/009999

PCT International Filing date

2007-11-15

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA