|Title of Invention||
A PORTABLE DEVICE ADAPTABLE TO TEST FUNCTIONAL PARAMETERS INCLUDING VOLTAGE AND CURRENT OF A PROTECTION PLUG
|Abstract||The invention relates to a portable device adaptable to test functional parameters including voltage and current of a protection plug, the protection plug used in a telecommunications network, the device comprising atleast one source of current (Urer), a pair of operational amplifiers (Ai, A2), atleast two potentiometers (Pi, P2), a series pass power transistor (T), an emitter resistor (Rs), and a load resistor (RL), said operational amplifier limiting the current output via the device.|
|Full Text||This invention relates to testing of a protection plug used h the telephone exchanges to protect the electronic exchanges from over voltage and over current. More particularly, the invention relates to a portable device adaptable to test functional parameters Including voltage and current of a protection plug.
These plugs are used at the interface between the subscriber line and the exchange tines. The protection from over voltage and over current is ordinarily ensured by providing a GDT (gas Discharge Tube) also called Arrester and a PTC
The testing device is designed to test the important electrical characteristics of both the GOT end the PTC thermistor In an assembled state which Is called the protection plug. Normally a protection plug comprises one three pole GDT and two PTC thermistors.
A GDT (Arrester) provides protection to personnel and equipment from abnormally high voltages which can be due to the result of lightning or electromagnetic induction. The surge limiting characteristics are designed to meet specific requirements. When the abnormal voltage reaches the specified level, a spark over occurs within the gas tube, and the surge is redirected to earth thus protecting the personnel and the equipment. It is thus necessary to
ensure that the protection plug Is built to meet various specified parameters to ensure that use of this component actually protects the personnel and equipment. The important parameters that need to be checked for compliance are: spark over or strke over voltage.
PTC or Positive Thermal Coefficent Thermistor is an electronic device. This device ensures that currant beyond specified value is prevented from flowing through it. This is achieved by the increase of resistance of the device which is proportional to the increase in temperature (Excess current raises the temperature of the device). By limiting the current in this way, the network and equipment is protected from External Overload and Short circuit. This makes the Exchange Equipment totally safe under all circumstance. The important parameter that need to be checked for compliance are resistance of PTC and tripping and holding current characteristics of PTC.
As observed above protection plug in a line goes a long way in protecting the network and exchange. This calls for the use of a healthy Protection plug so that the desired protection is achieved. It » a very elaborate process to check the protection plug for Its Ml operational specifications, even in a laboratory. The testing method b as explained hereinafter.
Testing a protection plug for its component characteristics in the field is quite difficult because a plurality of instruments will be required to test the protection plug. Maintenance, caHbration & operation of such plurality of instruments will be expensive and difficult.
An object of the present invention is to provide a device adaptable for testing functional parameters Including voltage and current plug of a protection plug which is user friendly, rugged and aesthetically pleasing and integrated to test important characteristic* in one setting.
A farther object of the present invention is to provide a device adaptable for testing functional parameters including voltage and current plug of a protection plug which is compact and portable.
A still further object of the present invention b to provide a device adaptable for testing functional parameters including voltage and current plug of a protection pug which is capable of testing both positive thermal coefficient thermistor and gas discharge tube.
A still another object of the present invention is to provide a device adaptable for testing functional parameters Including voltage and current plug of a protection plug which is capable of being mounted on the wall and secured against misuse.
Accordingly, there is provided a portable device adaptable to test functional parameters including voltage and current of a protection plug, the protection plug used in a telecommunications network, the device comprising atitast one
source of currant, a pair of operational amplifiers, atleast two potantiomatars, a series pass power transistor, an emitter resistor, and a load resistor, said operational amplifier limiting the current output via the device.
Thus, when a linearly rising voltage at the rata of 100 V/s from 0 to 350 VDC is applied, the GDT strkes at a voltage of anywhere between 180 to 350 vote, the device being made be capable of measuring this voltage. The device farther monitors strkeover and latch the reading. To avoid continuous strke over the Yoltoge is fcnmecHataly switched off. The resulting strfce-over voltage Is restricted within specified limits. The device then compares and confirms this.
The linearly rising high voltage (called ramp) protects the short circuit end the over load. The ramp maintains the wave shape even under open circuit condition. It should be floating that is, earth terminal is connectabte to the OV line. It is capable of fast response so that the ramp Is cut-off Immediately after the first straw Is over. The device is compact.
To test a PTC, the device is provided with a power source with
a) Short circuit protection
c) Reduced heating.
The PTC is tested by sending a programmable constant current source of 110
mA for a specified time. On maintaining its state for specified time, the PTC is pumped with a current of 250mA and monitored for tripping behavior. If the
PTC trips within the specified time, then a reset time is allowed and again a current of 90 mA is pumped in to check whether the PTC has restored. Alt the timings are monitored using internal timers.
AH the results are shown on the front panel. An auto test facility is provided to test the complete Protection plug consisting of GOT and two PTCc automatically and sequentially. The result of ail the components Is available for further
The heart of the device is a versatile, precision power supply. It b not sufficient if me power supply is just stabilized. It must also include some forms of protection against the faults arising in the plug under test. This normally is limited to current limiting and output short circuit protection. In order to fulfill its function correctly, the power supply has been selected with the underrated features: -
- a capacity to deliver constant stable voltage at substantially high voltages
of around 350 -400V,
• a capacity to deliver substantially high, around 300mA, stable constant current levels Into 250 Ohms Impedance,
- the output must be completely stable at ail load conditions,
- the output must heve some form of short circuit protection,
- digitally selectable and variable output current limiting means,
- output voltage control that is digitally triggerable and programmable for amplitude and waveform,
- accurate indication of output ventage and output currert^
- capable of sensing inputs for accurate four point measurements, to allow for cable compensation during precise measurements.
The present invention thus provides a portable testing device adaptable for testing protection plug used In telecom network. The tester comprises sources of currant (IW & R), a pair of Operational amplifier (At, A2) potentiometers(Pl and P2), a transistor (T), emitter resistors (Rs), and optionally a load(Rt), said tester being provided with two Operational amplifier* and a series pass power transistors, said current source UV* and R being similar, said Operational amplifier A2 being responsible for output current limiting.
In the above device used in telecom network the voltage across the emitter resistor (Rs) and transistor (T) is proportional to said output load current. Further, a proportion of reference voltage Is derived by setting of second potentiometer (P2) which is comparable to voltage across Rs by the second Operational amplifier (A2). The voltage across the emitter resistor (Rs) becomes higher than that set by second potentiometer (P2), the Operational amplifier reduces basic drive current to T until the difference is reduced to zero.
The precision power supply designed in the device, include! all the above features. It further approaches the stability and programmable problems with a circuit means.
The vast majority of power supplies use either "series" or *pasi" regulation. This means that the stabilizing power transistors are connected (effectively) in series or in parallel to the bad. In common with most designs the cfrcuit here utilises series pass regulation. The originality in the circuit design is the method used for stabilization.
Figure 1 illustrates a testing method of a protection plug according to the
Figure 2A shows a circuit diagram illustrating the principle of a conventional series regulator.
Figure 2B shows a circuit diagram illustrating another conventional series regulator.
Figure 2C illustrates an embodiment of a circuit means for power supply for a testing device for testing a protection plug according to the invention.
Figure 2D illustrates another embodiment of a circuit diagrams for the power supply for the testing device according to the invention.
Figure 3 schematically illustrate* a testing device of the present invention.
Figure 4 illustrates the block diagram of the complete tester
Figure 4.1 illustrates a circuit means of the Programmable Power supply according to the present invention.
Figure 5 shows the line diagram of the device according to the present invention.
The block diagram in figure 2A illustrates the principle of the conventional series regulator. Tha active element of the circuit is Operational amplifier A and HB output is tha source of the load currant, that is, in series with the bad Ri. The non-inverting input of the Operational amplifier is held at a reference voltage Ur*. The inverting input of the Operational amplifier is at a voltage level that te a proportion of the input voltage - derived by potentiometer P. Under these conditions the output of the Operational amplifier will become stable at the point where the voltage difference between the two inputs is Zero. That is, the Operational amplifier will maintain a condition where the reference voltage and that at the wiper of potentiometer P are equal (ref 1). It will be obvious that the output voltage will therefore be dependent on the position of P. With the potentiometer in mid position the output will be double the reference voltage. The disadvantages of this system are that the stability factor is dependent on the setting of potantkxnenter P, the output can never be lower than the reference voltage and the operation of P will not be linear.
Two of thase points may not ba so significant in soma caaas but an output minimum is not acceptable in the currant design.
The block diagram of figure 28 provides another solution. In this case, the Operational amplifier is used as unity gain amplifier or voltage follower which is known in the art and P becomes a voltage divider connected across the reference voltage. The output of the Operational amplifier win now be proportional to the voltage level at the wiper of P. In this configuration the output range will be between 0 and the reference voltage. This arrangement is still far from Weal. The Operational amplifier will now require a negative voltage supply rail, en added disadvantage, The reference voltage mutt be at least as high as the maximum required output which in our case will ba around 350V to 400V. Hence this design is ruled out.
It is at this point that the novel design scheme hat been envisaged. It goes a long way towards removing the disadvantages experienced by the earlier two designs by replacing the reference voltage, as far as the Operational amplifier Is concerned, with a reference current. The output voltage is now determined by the current passing through P. The advantage of the new circuit it no longer dependent on the reference voltage level.
Referring to figure 2D. The reference current in this case » derived from the output voltage via a series resistor R. The method used here Is unorthodox.
As previously mentioned, a current source is achieved by placing a resistor from the output. However, for this to happen in practice, the value of potentiometer
P has to be much lower than R. The Operational amplifier still tries to balance out the difference between the voltage levels at its inputs but now the output voltage will be equal to the level on its non-inverting Input.
The series resistor Is effectively placed between the two Inputs of the Operational amplifier. However, due to the high impedance of the inputs, no current can enter the Operational amplifier. In effect then, the current derived from the reference source follows the path shown as a dotted line in the block diagram. Since Ut ■ U2 (the Operational amplifier ensures this) the current level remains constant, totally independent t of P and the load. The current level is equal to U «f / R. The Operational amplifier will balance out the voltage across P and, In doing so, the reference currant (even at OV) using a reference voltage source and a resistor. Since the voltage regulation is based on current loop, no ground reference is needed. The whole power supply can be floating and the magnitude of output voltage wUI not pose a challenge to the control device.
By varying the reference current, the output voltage may be programmed to desired wave shape. The tight feedback of the current loop ensures a stable output voltage Irrespective of the load conditions.
Testing of GOT reqires a constant voltage source whereas testing of PTC needs constant current source. By introducing Just one more Operational amplifier in the above design, a constant current source is derived.
The process is now illustrated with reference to Figure 3.
The major difference between the block diagram of the precision powar supply in figure 3 and that of figure 20 is the fact that two Operational amplifiers and a series pass power transistor are included. The current source (U rtl and R) and the potentiometer PI are very similar.
The second Operational amplifier A2 is responsfcle for output current limiting. The voltage across the emitter resistor Rs of transistor T is proportional to theoutput load current. A proportion of the reference voltage is derived by the setting of P2 and this Is compared to the voltage across Rs by opap A2. when the voltage across Rs becomes higher than that set by P2, the Operational amplifier reduces the base drive current to T until the difference is reduced to zero.
Thus the above circuit means forms an essential feature of the subject device.
With reference to Figure 3. The actual realization of the method is shown via the circuit means of figure 4.1. Voltage reference is derived from pulse width modulated output of the microcontroller. This is the OV* of figure 3. Resistor R20, R21 & R22 form R in figure 3. The reference voltage arrives at non-inverting terminal of the Operational amplifier IC 1A (Al of fig.3.) While the inverting terminal of the Operational amplifier is connected to the system ground through R25. The output of IC 1A controls the power output stage, consisting of transistors Q2, Q3 and Q4 by providing the base drive current for Q2. Resistors Rl and R2 form the feed bade shunt Rs in the theoretical figure 3. R41 is the resistor in the feedback current bop (P). The Operational amplifier IC 1A tries to maintain the current constant in the loop by either increasing or decreasing the
output voltage. The actual value of the current w controlled by the reference voltage generated by the microcontroller through pulse width modulation technique. Thus the final output voltage is controlled by the microcontroller. The microcontroller is programmed in such a way as to start from zero volts and linearly rise the voltage upto 350V.
In the constant current section, the reference voltage is generated by the microcontroller using pulse width technique. The voltage drop across resistor Rl and R2 Is compared in IC IB (A2 of figure 3) with a voltage level set by current reference. The output of IC lb like that of IC 2A, is fed to the base of transistor Q2. When the output current is higher than that set by the current limit reference, the IC IB reduces the base drive effectively bringing down the current within limit. Thus current is maintained constant.
Diode D6 protects the input of the Operational amplifier against surge voltage. Resistors R23 and capacitor SC5 increase the response time of the circuit thus eliminating any unnecessary glitches or spices.
Capacitor SC2 avoids oscillation in Operational amplifier reducing the ripple content at the output.
Thus by realizing a current reference instead of a voltage reference, by using a simple yet novel technique, the instrument has been designed.
The invention described herein may have modifications or alterations which are within the knowledge of a person having the average skill in the art, such modification or alterations are intended to be within the scope of the present invention.
1. A portable device adaptable to test functional parameters including voltage and current of a protection plug, the protecticm plug used m a telecommunications network, the device comprising atleast one source of current (Uaf)/ a pair of operational amplifiers (Al, A2), atleast two potentiometers (PI, P2), a series pass power transistor (T), an emitter resistor (fU), and a load resistor (Rt.), said operational amplifier limiting the current output via the device.
2. The device as claimed in claim 1, wherein a voltage aaoss said emitter resistance (Rs) and the transistor (T) is proportiortal to said output current.
3. The device as claimed in claim 1 or 2, wherein a portion of a refsrence voltage is derived by setting the second potentiometer (P2}, the refererxe voltage being comparable to the voltage across the emitter resistance (Rs) by said secorKl operational amplifier (A2) thereby limiting the output bad current.
4. The device as claimed in any one of the preceding claims, wherein when the voltage aaoss said emitter resistor (Rs) reaches a value higher than that set by the second potentiometer P2, said operational amplifier (A2) causes a base drive current flowing to the transistor (T) to reduce the voltage till the difference attains a zero value.
5. The device as claimed in any one of the preceding claims, wherein a reference current for controlling the output voltage is derived from a series resistor (R), thereby adapting the reference voltage source (Ur«r) and the series resistor (R ) for generating a floating power supply capable of providing a wide range of output voltage without any ground reference.
6. The device as claimed in any of the preceding claims, comprising a mechanical holder constituting a switching module to hold the protection plug during test, the switching module being connected to a switching cffcuit a matrix of relays.
7. The device as claimed in 6, wherein the switching circuit, is controlled by a microcontroller having embedded firmware, and wherein the switching circuit is connected to a programmable power supply and an analog to digital converter.
8. The device as claimed in claims 1, 6 or 7, wherein the miaocontroller having an in-built memory, an analog to digital converter, a plurality of timers, and atleast one digital input output line connected to a liquid crystal display (LCD) for displaying the test results and, wherein a pair of l£Ds are provided to Indicate overall pass or fail result.
9. The device as claimed in claim 8, wherein the microconfroller is provided with a plurality of push button keys which act as an user interface during testing of the protection plug.
lO.A portabk devka adaptable to test functional parameters Including voltage and current of a protection plug as substantialhr herein desalMd with reference to the accompanying drawings.
|Indian Patent Application Number||897/MAS/2002|
|PG Journal Number||27/2007|
|Date of Filing||02-Dec-2002|
|Name of Patentee||M/S. KRONE COMMUNICATIONS LTD|
|Applicant Address||#10/C 11 PHASE PEENYA, BANGALORE 560 058.|
|PCT International Classification Number||H 02 H 9/00|
|PCT International Application Number||N/A|
|PCT International Filing date|