Title of Invention	A METHOD AND A SYSTEM FOR A MULTI-CHANNEL CURRENT MONITORING
Abstract	The present invention relates to a system (Fig 1) to obtain multi-channel current events and to reconstruct the current events that occur over multiple channels. The system makes use of Hall Effect sensors to convert the current pulse to voltage signals, signal conditioning and digitization circuitry to convert the data to digital format with varying sample rates in the former and latter parts of the pulse, thresholding logic to detect 'significant' events in current channels and digital logic to time-stamp and communicate the data corresponding to various channels to a Central Controller for further transmission. The system of the present invention also adopts event-based monitoring and packetised data transmission that enables simultaneous acquisition of large number of channels with considerable reduction in data rate. The present invention also provides a method for obtaining multi-channel current events and then transmitting the information in digital format to enable reconstruction of multi-channel current events.

Title of Invention

A METHOD AND A SYSTEM FOR A MULTI-CHANNEL CURRENT MONITORING

Abstract

The present invention relates to a system (Fig 1) to obtain multi-channel current events and to reconstruct the current events that occur over multiple channels. The system makes use of Hall Effect sensors to convert the current pulse to voltage signals, signal conditioning and digitization circuitry to convert the data to digital format with varying sample rates in the former and latter parts of the pulse, thresholding logic to detect 'significant' events in current channels and digital logic to time-stamp and communicate the data corresponding to various channels to a Central Controller for further transmission. The system of the present invention also adopts event-based monitoring and packetised data transmission that enables simultaneous acquisition of large number of channels with considerable reduction in data rate. The present invention also provides a method for obtaining multi-channel current events and then transmitting the information in digital format to enable reconstruction of multi-channel current events.

Full Text	A METHOD AND A SYSTEM FOR A MULTI-CHANNEL CURRENT MONITORING Technical Field The present invention relates to a method and system to obtain multi-channel current events and to reconstruct the current events that occur over multiple channels. The present invention particularly relates to a method and a system wherein single or multiple non-invasive sensors are used for monitoring multiple current events that are temporally apart and originating from multiple channels. The present invention further relates to a method to obtain multi-channel current events by means of single sensor or multiple sensors and to reconstruct said current events. Background and prior art Various forms of multi-channel current monitoring systems are known. A 'Current monitoring circuit for secondary battery' described in US 6,335,611 relates to a current monitoring circuit for monitoring a charging / discharging current of a secondary battery that achieves high precision monitoring and that restricts an increase in the circuit scale. According to this invention when an excess current has been detected, a switch is set to a non-conductive state, to thereby disconnect the battery from the external unit. The chargeable/dischargeable secondary battery may reside in a portable information terminal. US 6,100,701 describes a device for the monitoring of current drawn by an ignition coil for a spark ignition engine, and in particular describes a circuitry and a method for detecting a malfiinction in the charging of an ignition coil or its associated drive circuitry. The system comprises circuitry to measure the voltage of a battery for charging the coil, circuitry to measure an amount of current drawn by the coil over a time less than the time taken to charge fully the coil, software to determine according to the measured battery voltage a nominal dwell time for charging fully the coil prior to discharge of the coil, software to extrapolate from the measured current a calculated expected dwell time to charge fully the coil and a device to indicate an error condition if the difference between the expected and nominal dwell times is beyond a predetermined error limit. 'Current transducer and current-monitoring method' is illustrated in another US Patent No: 6,064,191 where a current transducer including a current transformer in which the conductor carrying the current to be monitored constitutes the primary is described. The transformer secondary is wound on a toroidal core. The transformer is operated below its cut-off frequency such that the output from the secondary is proportional to the differential of the current in the primary. The secondary output is integrated by an integrator to provide a measure of current in the primary and the integrator is initialized at predetermined intervals. A current measuring device for an electric machine, for example a reluctance machine, includes at least one of the current transducers. A Circuit arrangement for testing the operation of a current monitoring circuit for a power transistor is revealed in another US 5,892,450 which describes a circuit arrangement for testing the operation of a current monitoring circuit for a power transistor. The power transistor consists of several single transistors of the same size connected in parallel, through which a fraction of the total current supplied to the power transistor flows. A monitoring signal proportional to the current flowing through one of the single transistors is supplied to the current monitoring circuit, which generates an alarm signal when this monitoring signal exceeds a specified threshold value. The transistors are divided into groups and a control circuit is provided to regulate the current supplied to various groups. The circuit arrangement enables the operation of the current monitoring circuit to be checked in the integrated semiconductor circuit even before it is bonded and contacted. Current Monitoring systems are described elsewhere also. A European Patent EP1208386 on 'Sensor for Current Measurement and Electricity Meter' describes an electronic circuit formed on a printed circuit board that is configured as a current-to-voltage converter using a printed circuit track as a sensor, placed in parallel with a primary current carrying conductor, for example, a bus bar. The sensor comprises two sensing coils arranged in a 'figure-of-eight' arrangement with a cross-over region. The sensor has an output connecting to processing circuitry. Current flowing through the bus bar induces a magnetic field, which is detected by the sensing coils, the magnetic field being directly related to the magnitude of current flowing through the bus bar. Another patent EP1218760 on 'Measurement of Current in a Vehicle using Battery Cable as Shunt' details about the determination of current flowing into and out of a battery installed in a vehicle with the required cable between one of the battery terminals and a reference point on the vehicle by measuring the voltage across the cable. The resistance value of the cable can be known in which case the current is computed using Ohm's law and a differentia! current sensor can be used to respond to the voltage measured across the cable to accommodate for the different ranges of current. If the cable resistance is unknown, a reference current source along with an amplifier of fixed gain may be configured in such a way that the voltage output of the amplifier is a measure of current flow in the cable. In-situ Metallization Monitoring using Eddy CuiTent Measurements and Optical Measurements' is the subject of a EP 1244907 disclosing a method of obtaining information in-situ regarding a film of a sample using an eddy probe during a process for removing the film. The eddy probe has at least one sensing coil. An ac voltage is applied to the sensing coils of the eddy probe. One or more first signals are measured in the sensing coils of the eddy probe when the sensing coils are positioned proximate the film of the sample. One or more second signals are measured in the sensing coils of the eddy probe when the sensing coils are positioned proximate to a reference material having a fixed composition and/or distance from the sensing coil. The first signals are calibrated based on the second signals so that undesired gain and/or phase changes within the first signals are corrected. A property value of the film is determined based on the calibrated first signals. EPl247330 on 'Shaft Voltage and Current Monitoring System' describes a rotating machinery monitor that provides a warning indicative of a developing problem. The rotating machinery monitor has at least one current sensor for detecting shaft grounding current and at least one voltage sensor for detecting shaft voltage, a change detector for determining the rate of change in the shaft grounding current and a change detector for determining the rate of change in the shaft voltage and an evaluation system for producing a warning as a ftmction of the change in the shaft grounding current, the rate of change in the shaft voltage, the shaft grounding current and the shaft voltage. Another 'Current Measurement Device' is revealed in EP1277060. A device for measuring alternating current in a conductor comprising an even number of identical coils mounted on an electrically insulating coil support member is described herein. Half the coils are equally spaced around a first notional circle and are connected in series by a first conductive track and the other half of the coils are equally spaced around a second notional circle concentric with the first and are connected in series by a second conductive track. The support member has a recess to allow a conductor under test to be introduced into the centre of the concentric circles. The device fiarther includes means for deriving the alternating current in the conductor as a ftmction of the voltages induced in the first and second sets of series connected coils. The coils and the support member are manufactured by printed circuit or thick film technology. JP2001056348 is on 'Opfical Fiber Current Sensor and Electric Line Monitoring System to Use the same' which describes a converter that is comprised of a pair of magnetostrictive materials impressed with a bias magnetic field in the same direction, an interferometer in which two arms comprised of optical fiber coils are each fixed to the magnetostrictive materials, and a magnetic field generating coil to generate a signal magnetic field in the opposite direction in the magnetostrictive materials. A means for detecting the phase difference of light at the interferometer is provided. A laser beam outputted from a laser beam source is subjected to a phase shift proportional to a signal current at the converter, and the beam subjected to the phase shift is transmitted to an 0/E converter to obtain an output proportional to the signal current from a demodulator. JP2000235050 is on 'Process and Means for Monitoring the Current in a Power Distribution Network' which relates to a power supply bus (LB) and a control bus (CAN) that link a number of power users on a power network. A resistance connected to the power bus (LB) measures the total power taken by all the users and an output measurement signal is connected to the control bus (CAN). The resistance is integrated with a semiconductor controller and heat-transfer fins as a complete unit. An independent claim is made for a device for use with the power measurement and management system. JPl 1122954 dated February 17, 1999 on 'Monitoring of Current in an Inductive Load, PWM Driven through a Bridge Stage' explains a current monitoring method by using a pair of complementary periodic reference signals and amplifying by a sensing amplifier the signal existing on a current sensing resistor functionally connected in series with the load, for producing an amplified signal representative of the current in the load to be fed to an input of an error amplifier driving a power amplifier of said bridge stage, comprises sampling the signal output by the sensing amplifier with a Sample & Hold circuit comprising a sampling switch and a storing capacitor. The average value of the current in the load is monitored by sampling at an instant halfway an active driving phase and at an instant half way a current recirculation phase by closing the switch with a synchronizing pulse that coincides with the half instant of said phases of operation. A patent on 'Leakage Current Monitoring Device for Lightning Arrester' vide JP2000091058 where the leakage current measured value is taken with a preset short detecting time interval and in the case where this measured value is measured at the data storage time, the data is stored even if it is less than a detection level CL. In the case where the measured value is not measured at the data storage time, the data is stored if it is more than the detection level CL. In the case where the measured value is not measured at the data storage time and the leakage current measured value is reset for a value less than the detection level after exceeding the detection level, the data is stored by the specified number N of limes in any condition. The device is thus capable of efficiently collecting leakage current data in detail without omission. None of the above systems perform the function of multi-channel current monitoring based on Hall Effect sensors. Further these inventions do not state how a single sensor can be used for monitoring multiple current events that are temporally apart. Also they do not describe how an event based storage and transmission of the data corresponding to multiple channels can lead to significant reduction in requirements like bit-rate and communication bandwidth (when it is essential to monitor from a distant place through say, an RF telemetry link), storage memory, circuit complexity etc. Objects of the present invention The primary object of the present invention is to provide a system to obtain multi-channel current events based on non-in^'asive sensors. An object of the present invention is to provide a system for obtaining muiti-channel current events wherein either single or multiple non-invasive sensors is/are used to measure current pulses from multiple current events originating from multiple channels. Another object of the present invention is to provide a system for obtaining multi-channel current events that are temporally apart. Yet another object of the present invention is to provide a system for obtaining multi-channel current events to reconstruct the waveform of current pulses that occur over multiple channels. Still another object of the present invention is to provide a system for obtaining multi-channel current events for an event-based storage and packetized transmission of data corresponding to the multiple channels. Further object of the present invention to provide a system for obtaining multi-channel current events having reduced system hardware requirements including number of sensors required, bit rate, reduced memory storage etc. It is also an object of the present invention to provide a method for monitoring multiple current events in multiple channels by using single sensor/multiple sensors for multiple channels. Summary of the invention The present invention relates to a method and a system to obtain multichannel current events and to reconstruct the waveform of current pulses that occur over multiple channels. The present invention particularly relates to a system wherein single or multiple non-invasive sensors are used for monitoring multiple current events that are temporally apart and originating from multiple channels. The system of the present invention comprises sensors, signal conditioning and data acquisition modules and a transmission format that can cater to the monitoring requirements of multiple current channels. This is achieved by using one sensor for many channels thus minimizing the total number of sensors required. The system also performs event based storage and packetised transmission of the acquired data corresponding to a predefined event. The system allows the defmition of the event to be flexible, like data crossing a certain threshold magnitude, occurrence at a certain time etc. Further, in the present system, monitored pulsed currents are transmitted in a digital format through a system like a telemetry system to enable reconstruction of time-stamped current signatures. The system adopts Hall Effect sensors to convert the current pulse to voltage signals, signal conditioning and digitization circuitry to convert the data to digital format. Some of the significant features of the present system include a provision for varying sample rates in the initial and later parts of the pulse, thresholding logic to detect 'significant' events in current channels and digital logic to time-stamp and communicate the data corresponding to various channels to a Central Controller for transmission to a receiver. Event-based monitoring and packetised data transmission are further features of the system that enable simultaneous acquisition of large number of channels with considerable reduction in data rate. The present invention further relates to a method to obtain multi-channel current events by means of single sensor or multiple sensors and to reconstruct said current events. Brief Description of the accompanied drawings Fig. 1 is a block diagram of the multi-channel current monitoring system Fig. 2 is a view of a non-invasive current sensor s'»owing the windings used to measure the current passing through each channel corresponding to the number of windings. Fig. 3(a) & 3 (b) is a graphical sketch of current pulses in two separate lines. Fig. 4 is an exemplary format in which the data corresponding to various channels are stored in memory. Figs. 5 and 6 depict a system flow diagram for obtaining multi-channel current events. Detailed description of the invention The present invention provides a method and a system to acquire and reconstruct the waveform of current pulses that occur over multiple channels. The invention is now explained with reference to the accompanied diagrams. Initially referring to Fig. 1, the system as shown, consists of 3 modules: Relay Module (RM), Current Sensing Module (CSM), AQUisition ELectronics Module (AQUEL) and. (CSM and RM are shown by dotted bounding box and all the other elements together constitute AQUEL). Relay Module (RM): This block is optional to the system functionality. It consists of high current sensors (1) and relays (2) that can switch the currents to be measured (ON/OFF RELAY) - one each for prime and redundant channels. Thus the module switches and measures the total current drawn from each of the batteries and flowing through the CSMs. Current Sensing Module (CSM): The CSM (3) comprises Hall Effect sensors and a signal conditioning circuit. A Single Hall Effect sensor is used for non-invasive monitoring of current flowing through the multiple lines. In the present invention, a total of 40 lines are adopted in an illustrative manner. The first 20 lines are designated as (3c) and the other 20 lines are designated as (3d). The sensors are mounted in the Current Sensing Module (CSM) for measuring the current pulses in the form of analog signals as received from a system (for instance, the Relay Module (RM), as shown in the Fig. 1, a charging / ignition battery, a start-up circuit for electrical machinery etc.) The embodiment of incorporation of Hall Effect Sensors, in an illustrative manner is depicted in Fig. 2. The current carrying lines are wound on a rectangular core. A single sensor can carry several lines of varying current carrying capacity and turns. The sensor contains signal conditioning circuitry amplifies the signals and gives an output voltage that is proportional to the total current flowing through all the lines wound on it. The signal conditioning circuitry packaged along with the sensor consists of a signal amplifier that magnifies the amplitude of low-level signals produced by the Hal! Effect sensing element. For instance, by referring to Sensor as depicted in Fig. 2, the sensor provides a full scale output of 5 V when lOA current flows through line (L3). Whereas, when 1 A flows through line (LI) whose full scale is 5 A, it gives an output of 5x1/5=1 V. For purposes of illustration 20 sensors each are shown in Fig. 1 for prime and redundant chains. In CSM (3), dual redundancy is used for all the elements to ensure that malfunctioning of a single element does not lead to system failure. Thus for the current sensors two sets of components - one 'prime' (3a) and the other, 'redundant' (3b) are used to ensure that critical functionality is maintained in spite of failure of a single element. The system interfaces (communicates the data) to a Central Control Unit (CCU) through either a wired link (as shown in the figure) or a wireless link. Dual redundancy is used for all the elements other than acquisition electronics to ensure that malfunction of a single element do not lead to system failure. Thus for the current sensors, relay module and CCU interface two sets of components - one 'prime' and the other, 'redundant' are used to ensure that critical functionality is maintained in spite of failure of a single element. Current Sensors - Prime (3a) and Redundant (3b) sensors are housed in CSM. These sensors are Hall Effect Sensors used for non-invasive monitoring of current. The current carrying lines are wound on a rectangular core of the sensors (3a) and (3b). Now referring to Fig. 2 a single sensor can carry several lines of varying current carrying capacity and turns (A sampie illustration is given in Fig. address is stepped sequentially so that the voltage output of each sensor becomes available to the succeeding stage at a predetermined sampling rate. Analog to Digital Converters (ADCs): A plurality of Analog to Digital Converters (6) (ADCs) disposed to receive the scanned analog voltage signals from the analog multiplexers (4) and further to convert into digitized format. The digitized sample size may vary from 4 bits to 16 bits i.e. from half a byte to two bytes, whereas 8 bits being a preferred option depending on the resolution (Resolution being the smallest change in current magnitude that can be detected by the system) and accuracy requirements of the data acquisition system. This depends on the sensitivity of components comprising the system as well as the sample size used in data converter. For example, an 8-bit system is capable of resolving 256 steps i.e. 19.5 mV in a 5 V full-scale. 'Accuracy' means the nearness or proximity of a measured value to the actual one. It depends on resolution as well as a host of other factors such as drift in component parameters, the calibration methods adopted etc. Analog buffers: A plurality of Analog Buffers (5) is used to provide high input impedance to preceding MUX (4) outputs and low output impedance to succeeding analog to digital converters (6). Such an impedance matching is necessary for maximum voltage transfer from multiplexer (4) to analog-to-digital converters (6). Analog-to-digital converters (6) perform the sampling and digitization functions of the scanned sensor outputs. They generate the binary coded sample values corresponding to the sensor outputs and are controlled by the signals generated by the FPGA (7). Field Programmable Gate Array (FPGA): An FPGA (7) acting as Write / Read / Decoder / Encoder Logic generates the digital control signals for sequentially scanning the sensor outputs, for sampling and digitization and detect an 'event' in a channel such as data crossing a certain preset threshold value, writing the coded sample values to appropriate blocks of Random Access Memory (RAM) (8) along with header information like time stamp and channel number and reading the data from RAM (8) on command from CCU (9). It also generates the address for RAM (8) and handles the decoding of command from Central Control Unit (9) and encoding of reply to be sent to it. The FPGA (7) detects a pre-defined event from the channel data and stores it on RAM (8) with suitable header information to enable subsequent independent reconstruction of the current waveform in each channel. A Field Programmable Gate Array (FPGA) (7), acting as a processor is disposed in the system to receive the digitized samples and fiarther to process as per the predetermined factors selected from threshold logic, time of occurrence of the event etc. (A thresholding logic typically uses a digital comparator to detect the data sample going above a certain predetermined value. In FIG. 3(a), Al (15) is the threshold magnitude of current and it is A2 (19) in FIG. 3(b). The instant of current waveform crossing the threshold are indicated by the time stamps, Tl (17) and T2 (20) respectively in the figures. Thus the events are said to have begun at these time instants. Similarly the event definitions may be synchronized to an absolute time in this system or in another one. In this case the event is said to be initiated at such predetermined time irrespective of the current magnitude at that time). The generation of all the control signals required for digitization, setting the channel threshold values, data recording onto memory and transacting the data with controller are handled in a FPGA. Referring to Fig. 1, the decoding means for the command from a Central Control Unit (9) and encoding of the reply to be sent to it are also provided by the FPGA (7) if a digitally coded scheme of data communication is used in the link. Such a scheme may, for example, use bi-phase signaling format with the data bits framed by suitable synchronization and parity bits to ensure error-free communication between the systems Random Access Memory (RAM): The memory (8) acting as storage means stores the data corresponding to the sensor channels along with the fime stamp information. The storage means is any known memory devices that can be used in any digitally implemented systems/processes. In the present invention, this storage means, a memory device, a random access memory device, is divided into banks - at least two in number, one for read and one for write and further into blocks - one for each channel. Each block gets written when an event is detected in the corresponding sensor channel. The read operation is synchronized to com.mand from CCU (9). The overall memory, bank and block sizes are dependent on system requirements such as number of channels, sampling rate etc. The storage means consists of banks and blocks for Sioring processed digital data. The digitized data samples are compared with a pre-determined threshold value. Each channel is allocated with a block of memory in the memory area RAM (8), whose length can vary from a few bytes to 10 Kbytes, with preferred storage area being 800 bytes, depending on the sampling rate and the expected maximum width of current pulse in that channel. (Sampling rate is the frequency at which samples of the current pulse are taken. The maximum width of current pulse is the longest duration over which the event is true, say; the current magnitude stays above a certain threshold value. For example in Fig. 3, the samples of current waveform are indicated by vertical dashed lines and Ts (14) is the time duration between any two of them. Then the sampling rate is fs=l/Ts. The threshold values are indicated by horizontal dotted lines as Al (15) for first channel in Fig. 3(a) and A2 (19) for second channel in Fig. 3(b). Tl (17) is the time instant of event start for first channel and T2 (20) that for second channel. Wl (16) is the pulse width from Tl (17) that the event is true for first channel in Fig. 3(a) and W2 (21) that from T2 (20) for second channel in Fig. 3(b). Thus the numbers of samples are Wlxfs and W2xfs for the first and second channels respectively). The memory is divided into two banks so that data recording and reading can proceed simultaneously without loss of data. The bank size may vary up to i Mbytes, preferably 32 Kbytes depending on the block size and the number of channels. An example for the format in which data corresponding to various channels are stored in memory is depicted in the form of a block diagram as shown in Fig. 4. Here the data samples corresponding to each channel are stored in a block of memory along with header information such as times of event occurrence i.e. start of current pulse, number of samples above threshold etc. The time stamp bytes may correspond to the timer value i.e. the state of a timer counter implemented in the FPGA at the instant of occurrence of the event (Tl (17) and T2 (20) in Fig. 3) with respect to an initial time reference such as a timer reset pulse. A number of such memory blocks (depending on number of channels) constitute a bank and a number of such banks (depending on the maximum number of events that can occur in a sensor within the time period for transmission of data) constitute the entire memory. (Bank number is the area of RAM where recording is done. Bank number is to be attached to the header during transmission of data only, not during storage of data into the RAM). Such a scheme of storing data ensures that all the relevant data required for reconstruction of pulsed events is preserved without loss in a compressed format that minimises the requirement of memory capacity. Central Control Unit (CCU) Interface: As shown in Fig. 1, this block contains the electrical interface circuitry for the link to CCU (9). It typically consists of Pulse Transformer (10) and Line Receiver (11) on the input side to receive the command from CCU (9) and Line Driver (12) and Pulse Transformer (10) on the output side to send the reply to CCU (9). It is understood here that only the CCUl I/F (9) is shown in detail, CCU2 I/F (13) is similar in construction. As an illustration, a pair of CCU units (9 & 13) has been adapted in the system, of which one is primary and other being a redundant unit. A Centra! Control Unit arranged to receive the processed digital signals from the processor sequentially at the reading rate up to 1Mbps, with a preferable reading rate of 4 Kbps depending on the bank size and the separation in time between the events. The separation is indicated by S (18) in Fig. 3 and becomes relevant if the current pulses shown in Fig. 3(a) and that in Fig. 3(b) occur on lines passing through the same sensor. The data is tagged with bank number, channel number, number of samples and time value to form a data packet that facilitates the reconstruction of current pulse waveform on a per channel basis. A typical format of such a data packet or frame is shown below. Here the header information consists of (i) the bank number that helps to identify which of the memory banks is being read currently (ii) the channel number, that helps to identify which of the memory blocks is being read currently (iii) number of data samples of the particular channel in the current data frame and (iv) the time stamp that indicates the start time of event occurrence in that channel. The header bytes are followed by the pre-specified number of data bytes. Such a format of communication data frame ensures faithful reconstruction of pulsed events with minimum requirements of signal bandwidth and data rate for the communication channel. The system also supports random reading with suitable header identification along with the data as explained. controller unit should continue for a certain minimum time (depending on the reading rate and memory bank size) even after the occurrence of the last event to avoid data loss. (This is because there is a time lag between an event being written into memory and it being read by CCU. This latency in the worst case works out to the total memory capacity divided by the reading rate. Thus to ensure that the data corresponding to even the last event is transmitted properly, the communication with the CCU should be sustained at least one latency period after its occurrence). The system for obtaining multi-channel current events for further reconstruction of the same is depicted in Figs, 5 and 6. A method of measuring and obtaining current pulses in a multi channel environment by using a single non-invasive sensor for multiple channels The method of the present invention permits the measurement of the total current flowing through all the channels and ftirther monitored using sensors of higher current rating. The current sensors work on the principle of Hall Effect and allow continuous monitoring of current. Due to Hall Effect the current to be measured (herein after called the 'primary current') creates a magnetic field around a semiconductor, carrying an excitation current. This magnetic field creates a voltage output and thereby a 'secondary current'. This secondary current is proportional to and balances the primary current. Multiple current carrying lines are accommodated on the same sensor by winding the current carrying wires through it (as shown in Fig. 2). The full scale of each line is set by the number of w indings or turns of the corresponding wire that passes through the sensor. For example, if the sensor full scale is 10 A and the maximum amplitude of current in a line is 2 A, then 5 turns of the wire may be taken through the sensor. The sensor full scale may vary from lA to 200A and the line currents may vary from 0.1 A to 200 A. This indicates that the number of turns of a single line through a sensor may vary from 1 to 20 (5 being a typical value). The full scale current amplitude may vary from 1 A to 200 A (5 A being a typical value) and is adjustable by using a suitable sensor configuration. The number of such channels that the system can cater to may vary from 2 to 100 (40 being a typical value) and the current pulse width over each channel may vary from 0.5 ms to 100 ms (40 ms being a typical value). The sampling period for the data acquisition can vary from 0.01 ms to 1 ms (0.05 ms being a typical value). The system also allows time tagging of the pulse events in various channels to a resolution that may vary from 0.01 ms to 1 ms (0.1 ms being a typical value). The transmission of the data thus acquired and stored in system memory may be event-based. The event is identified by the data crossing a specified threshold that may vary from 1% to 50% (10% being a typical value) of the full scale current amplitude for that channel. The transmission rate can be as low as 100 samples/s to 10 K samples/s (4 K samples/s being a typical value). This indicates a reduction in bit rate by as much as 1000 (10 being a typical value) that is made possible by event based transmission of data in multiple channels. This requires the events (current pulses) in a single channel to be temporally apart by 10 ms to several seconds (2 s being a typical value) depending on the transmission rate. It may be noted that the current pulses in the various lines passing through a single sensor need to be temporally apart as described above for the event based reconstruction of each current pulse. If the pulses occur simultaneously, then the sensor output will indicate the total current flowing through that sensor. The system is designed in such a manner as to allow flexibility in sampling rate during the various portions of current pulse. For example, the sample rate may be set at 18 KHz during the first 10 ms and at 6 KHz for the latter 30 ms of a current pulse. This allows the various parts of a pulse to be reconstructed with different levels of detail or time resolution. The threshold can be set digitally and may be made programmable on a per channel basis. When the data in a channel exceeds this threshold value the data samples are recorded in the form of blocks onto a Random Access Memory (RAM) (8) as shown in Fig. 1. In addition to the data the time of occurrence of the event is also recorded onto memory. This time is obtained by recording the timer value at the instant the rising edge of current pulse crosses the set threshold value. The system may be designed to allow flexibility regarding the definition of 'event' also. For instance, a predefined time may be used to trigger the data recording instead of threshold detection. Here, the occurrence of event is defined with respect to timer crossing a preset value. The system design may also incorporate an 'inhibition' period during which further recording of data in a channel is not allowed for a certain predefined time even if the event occurs in the channel. This 'inhibition' period may vary from tens of milliseconds to a few seconds depending on the guaranteed 'inactive' period for that channel. This avoids recording of 'spurious', unwanted events that may cause the useful event data to be over-written before it is read. The flexibility of transmitting multiple events without loss is also accommodated by having multiple memory banks (instead of two). For example 4 memory banks will allow up to 4 events on a single channel. This allows the readins rate to be lower or the events to be closer in time. Example A sample calculation for the separation of events in a single channel is shown below to illustrate how it depends on the various system parameters. The following parameters are assumed: Current amplitude, A = 5 A Resolution of measurement, R = 0.02 A From these two parameters we can calculate the sample size using the formula, Sample size - Log2(A/R) Hence, Sample size, S = log2(A/R) = log2(250) = 8 bits = 1 byte (1) Now assuming the following parameters, Maximum pulse width to be measured, W = 40 ms Sampling rate, K = 10 KHz After obtaining the value of Sample size, S from the equation (1), now we can calculate the Block length for a single channel by using the formula. Block Length = W x K x S where W - Maximum pulse width to be measured (Assumed) K - Sampling Rate (Assumed) S - Sample Size (Calculated from (1)) Hence, Block length for a single channel, B = WxKxS== 400 bytes (2) Again assuming the following parameter, Number of channels, N = 40 The value of the total memory bank size is calculated using the formula, Total Memory Bank Size = Block length (Calculated in (2)) x Number of channels (Assumed) Hence, Total memory bank size, T = B x N = 16000 bytes (3) Further assuming the Reading rate, X - 10 Kbytes/s (This may correspond to 160 bytes being read in a major frame of duration 16 ms in the case of a conventional PCM telemetry system). The allowable time separation between events in a channel is calculated as follows The allowable separation between events in a channel = T/X = 1.6 seconds Where, T - Total Memory Bank Size (Calculated in (3)) X - Reading Rate (Assumed) The above calculation assumes that only two memory banks are available - one of which is recorded while the other is being read. Thus the system as described above allows flexible monitoring of pulsed currents in multiple channels. It makes use of the concepts of event-based monitoring and packetized data transmission that enable simultaneous acquisition of large number of channels with considerable reduction in bit rate, when the data is to be transmitted to a central location. Advantages 1. The present invention performs the function of multi-channel current monitoring using a single sensor. 2. The present invention uses lesser bit rate and storage memory, due to the use of event-based storage and transmission system. 3. The system of the present invention is of reduced complexity as a result of reduction in hardware / bandwidth requirements. 4. The present invention allows definition of flexible events, like data crossing a certain threshold magnitude, occurrence at a certam time instant etc. 5. The present invention has the flexibility of transmitting multiple events without loss, by using multiple memory banks. 6. The present system allows for simultaneous reading from and writing into the m.emory, thus saving time and reducing the latency for data transmission. 7. The system of the present invention has applications in monitoring pulsed current in battery charging and spark ignition systems of automobiles, power switching systems, turn on/off systems for electric machinery like motors and generators, electric power transmission networks, characterisation / test systems for power semiconductor devices / circuit in electronic industry, performance monitoring systems for industrial / chemical process control, safety systems such as lightning arrestors, pyro initiated event sequencing systems etc. We claim 1. A system for obtaining multi-channel current events for reconstruction and monitoring, comprising: non-invasive sensors with a plurality of input current lines wound on the sensors to provide an output of voltage channels with voltage pulse events, a plurality of analog multiplexers with address bus to receive the voltage channels, an ON/OFF enabling switch on each analog multiplexer to enable/disable the corresponding analog multiplexer, a digital processor with a clock to scan the address bus of said analog multiplexer to enable the switch and to select the desired scanned voltage channel carrying voltage pulsed events, a plurality of analog to digital converters for converting said voltage pulsed events of the selected voltage channel into digital data, said digital processor to sample, detect and time-stamp the occurrence of pulsed events in said voltage channel that occur at a predetermined triggering instant or a threshold vaLie of voltage of said voltage channel, and to trigger the recording of data, a storage means for storing the triggered digital data, and a central control unit for receiving the digital data for reconstruction to original analog signals. 2. The system as claimed in claim 1, wherein a single non-invasive and/or multiple sensors are used for multiple current lines with the current pulses in the various lines passing through a single sensor being separated in time. 3. The system as claimed in claim 2, wherein the non-invasive sensor is a Hall Effect sensor. 4. The system as claimed in claim 1, wherein the number of turns of each of the plurality of current lines on the sensor varies from 1-20. 5. The system as claimed in claim 4, said plurality of current lines is based on the full scale amplitude of current pulses, pulse width and time separation instant. 6. The system as claimed in claim 5, wherein the full-scale current amplitude is in the range of 5A-200A. 7. The system as claimed in claim 1, wherein the number of voltage channels is in the range of 2-100, preferably 40 channels. 8. The system as claimed in claim 1, wherein the storage means consisting of banks and blocks for storing processed digital data. 9. A method for obtaining multi-channel current events for reconstruction and monitoring, said method comprising the steps of: sensing current pulses of multiple input current lines by means of non-invasive sensors to generate voltage channels, sampling and scanning said voltage channels to select a single voltage channel, converting voltage signals of said single voltage channel into digitized data by means of Analog to Digital Converters, storing a pre-determined digitized voltage signal level as a threshold value to record the digitized voltage signals in a storage memory along with header information consisting of the number of the selected channel and number of samples of the voltage signals of the selected channel, time-stamping of the recorded events, said processor further adapted to effect an inhibition period thereby preventing recording of the data, and transmitting to Central Control Unit in the form of a data packet for reconstruction into analog signals. 10. A method for obtaining multi-channel current events for reconstruction and monitoring as claimed in claim 9, wherein the storage of a pre-determined digitized voltage signal is performed by storing triggering instant of occurrence of digitized voltage signal and recording the occurrence of digitized data at said pre-determined triggering instant of occurrence. 11. The method as claimed in claims 9, wherein the rate of sampling is in the range 1 KHz - 100 KHz, preferably 20 KHz. 12. The method as claimed in claims 9, wherein the width of the current pulse over each current line is in the range of 0.5-100 ms, preferably 40ms. 13. The method as claimed in claims 9, wherein the period of sampling is in the range of 0.01-1 ms, preferably 0.05 ms. 14. The method as claimed in claims 9, wherein the rate of scanning is in the range of 2KHz to 10 MHz, preferably 800 KHz. 15. The method as claimed in claim 9, wherein the threshold value is predetermined in the range of 1-50% of full-scab current amplitude of input current lines. 16. The method as claimed in claim 9, wherein the full-scale current amplitude is in the range of 5A-200A. 17. The method as claimed in claims 9, wherein the number of samples is the product of rate of sampling and width of the current pulses. 18. The method as claimed in claims 9, wherein the time stamping of the pulse events in various channels is done to a resolution in the range of 0.01-1 ms, preferably 0.1 ms. 19. The method as claimed in claims 9, wherein a/' inhibition period is used to prevent recording of data in a channel even when the event occurs to prevent spurious and unwanted events that may cause the useful data to be over written before they are read. 20. The method as claimed in claims 9, wherein the transmission rate of the data is in the range of 100 - 10 K samples/s, preferably 4 K samples/s. 21. The method as claimed in claims 9, wherein the data packet consisting of with bank number, channel number, number of samples and time stamp as header information along with data. 22. The method as claimed in claim 10, wherein the pre-determined triggering instant in a single channel is in the range of 10ms to 10 sees, preferably 2 sees to trigger the data recording.

Full Text

A METHOD AND A SYSTEM FOR A MULTI-CHANNEL CURRENT
MONITORING Technical Field
The present invention relates to a method and system to obtain multi-channel current events and to reconstruct the current events that occur over multiple channels. The present invention particularly relates to a method and a system wherein single or multiple non-invasive sensors are used for monitoring multiple current events that are temporally apart and originating from multiple channels. The present invention further relates to a method to obtain multi-channel current events by means of single sensor or multiple sensors and to reconstruct said current events. Background and prior art
Various forms of multi-channel current monitoring systems are known. A 'Current monitoring circuit for secondary battery' described in US 6,335,611 relates to a current monitoring circuit for monitoring a charging / discharging current of a secondary battery that achieves high precision monitoring and that restricts an increase in the circuit scale. According to this invention when an excess current has been detected, a switch is set to a non-conductive state, to thereby disconnect the battery from the external unit. The chargeable/dischargeable secondary battery may reside in a portable information terminal.
US 6,100,701 describes a device for the monitoring of current drawn by an ignition coil for a spark ignition engine, and in particular describes a circuitry and a method for detecting a malfiinction in the charging of an ignition coil or its associated drive circuitry. The system comprises circuitry to measure the voltage of a battery for charging the coil, circuitry to measure an amount of current drawn by the coil over a time less than the time taken to charge fully the coil, software to determine according to the measured battery voltage a nominal dwell time for charging fully the coil prior to discharge of the coil, software to extrapolate from the measured current a calculated expected dwell time to charge fully the coil and

a device to indicate an error condition if the difference between the expected and nominal dwell times is beyond a predetermined error limit.
'Current transducer and current-monitoring method' is illustrated in another US Patent No: 6,064,191 where a current transducer including a current transformer in which the conductor carrying the current to be monitored constitutes the primary is described. The transformer secondary is wound on a toroidal core. The transformer is operated below its cut-off frequency such that the output from the secondary is proportional to the differential of the current in the primary. The secondary output is integrated by an integrator to provide a measure of current in the primary and the integrator is initialized at predetermined intervals. A current measuring device for an electric machine, for example a reluctance machine, includes at least one of the current transducers.
A Circuit arrangement for testing the operation of a current monitoring circuit for a power transistor is revealed in another US 5,892,450 which describes a circuit arrangement for testing the operation of a current monitoring circuit for a power transistor. The power transistor consists of several single transistors of the same size connected in parallel, through which a fraction of the total current supplied to the power transistor flows. A monitoring signal proportional to the current flowing through one of the single transistors is supplied to the current monitoring circuit, which generates an alarm signal when this monitoring signal exceeds a specified threshold value. The transistors are divided into groups and a control circuit is provided to regulate the current supplied to various groups. The circuit arrangement enables the operation of the current monitoring circuit to be checked in the integrated semiconductor circuit even before it is bonded and contacted.
Current Monitoring systems are described elsewhere also. A European Patent EP1208386 on 'Sensor for Current Measurement and Electricity Meter' describes an electronic circuit formed on a printed circuit board that is configured as a current-to-voltage converter using a printed circuit track as a sensor, placed in parallel with a primary current carrying conductor, for example, a bus bar. The sensor comprises two sensing coils arranged in a 'figure-of-eight' arrangement

with a cross-over region. The sensor has an output connecting to processing circuitry. Current flowing through the bus bar induces a magnetic field, which is detected by the sensing coils, the magnetic field being directly related to the magnitude of current flowing through the bus bar.
Another patent EP1218760 on 'Measurement of Current in a Vehicle using Battery Cable as Shunt' details about the determination of current flowing into and out of a battery installed in a vehicle with the required cable between one of the battery terminals and a reference point on the vehicle by measuring the voltage across the cable. The resistance value of the cable can be known in which case the current is computed using Ohm's law and a differentia! current sensor can be used to respond to the voltage measured across the cable to accommodate for the different ranges of current. If the cable resistance is unknown, a reference current source along with an amplifier of fixed gain may be configured in such a way that the voltage output of the amplifier is a measure of current flow in the cable.
In-situ Metallization Monitoring using Eddy CuiTent Measurements and Optical Measurements' is the subject of a EP 1244907 disclosing a method of obtaining information in-situ regarding a film of a sample using an eddy probe during a process for removing the film. The eddy probe has at least one sensing coil. An ac voltage is applied to the sensing coils of the eddy probe. One or more first signals are measured in the sensing coils of the eddy probe when the sensing coils are positioned proximate the film of the sample. One or more second signals are measured in the sensing coils of the eddy probe when the sensing coils are positioned proximate to a reference material having a fixed composition and/or distance from the sensing coil. The first signals are calibrated based on the second signals so that undesired gain and/or phase changes within the first signals are corrected. A property value of the film is determined based on the calibrated first signals.
EPl247330 on 'Shaft Voltage and Current Monitoring System' describes a rotating machinery monitor that provides a warning indicative of a developing problem. The rotating machinery monitor has at least one current sensor for

detecting shaft grounding current and at least one voltage sensor for detecting shaft voltage, a change detector for determining the rate of change in the shaft grounding current and a change detector for determining the rate of change in the shaft voltage and an evaluation system for producing a warning as a ftmction of the change in the shaft grounding current, the rate of change in the shaft voltage, the shaft grounding current and the shaft voltage.
Another 'Current Measurement Device' is revealed in EP1277060. A device for measuring alternating current in a conductor comprising an even number of identical coils mounted on an electrically insulating coil support member is described herein. Half the coils are equally spaced around a first notional circle and are connected in series by a first conductive track and the other half of the coils are equally spaced around a second notional circle concentric with the first and are connected in series by a second conductive track. The support member has a recess to allow a conductor under test to be introduced into the centre of the concentric circles. The device fiarther includes means for deriving the alternating current in the conductor as a ftmction of the voltages induced in the first and second sets of series connected coils. The coils and the support member are manufactured by printed circuit or thick film technology.
JP2001056348 is on 'Opfical Fiber Current Sensor and Electric Line Monitoring System to Use the same' which describes a converter that is comprised of a pair of magnetostrictive materials impressed with a bias magnetic field in the same direction, an interferometer in which two arms comprised of optical fiber coils are each fixed to the magnetostrictive materials, and a magnetic field generating coil to generate a signal magnetic field in the opposite direction in the magnetostrictive materials. A means for detecting the phase difference of light at the interferometer is provided. A laser beam outputted from a laser beam source is subjected to a phase shift proportional to a signal current at the converter, and the beam subjected to the phase shift is transmitted to an 0/E converter to obtain an output proportional to the signal current from a demodulator.

JP2000235050 is on 'Process and Means for Monitoring the Current in a Power Distribution Network' which relates to a power supply bus (LB) and a control bus (CAN) that link a number of power users on a power network. A resistance connected to the power bus (LB) measures the total power taken by all the users and an output measurement signal is connected to the control bus (CAN). The resistance is integrated with a semiconductor controller and heat-transfer fins as a complete unit. An independent claim is made for a device for use with the power measurement and management system.
JPl 1122954 dated February 17, 1999 on 'Monitoring of Current in an Inductive Load, PWM Driven through a Bridge Stage' explains a current monitoring method by using a pair of complementary periodic reference signals and amplifying by a sensing amplifier the signal existing on a current sensing resistor functionally connected in series with the load, for producing an amplified signal representative of the current in the load to be fed to an input of an error amplifier driving a power amplifier of said bridge stage, comprises sampling the signal output by the sensing amplifier with a Sample & Hold circuit comprising a sampling switch and a storing capacitor. The average value of the current in the load is monitored by sampling at an instant halfway an active driving phase and at an instant half way a current recirculation phase by closing the switch with a synchronizing pulse that coincides with the half instant of said phases of operation.
A patent on 'Leakage Current Monitoring Device for Lightning Arrester' vide JP2000091058 where the leakage current measured value is taken with a preset short detecting time interval and in the case where this measured value is measured at the data storage time, the data is stored even if it is less than a detection level CL. In the case where the measured value is not measured at the data storage time, the data is stored if it is more than the detection level CL. In the case where the measured value is not measured at the data storage time and the leakage current measured value is reset for a value less than the detection level after exceeding the detection level, the data is stored by the specified number N of

limes in any condition. The device is thus capable of efficiently collecting leakage current data in detail without omission.
None of the above systems perform the function of multi-channel current monitoring based on Hall Effect sensors. Further these inventions do not state how a single sensor can be used for monitoring multiple current events that are temporally apart. Also they do not describe how an event based storage and transmission of the data corresponding to multiple channels can lead to significant reduction in requirements like bit-rate and communication bandwidth (when it is essential to monitor from a distant place through say, an RF telemetry link), storage memory, circuit complexity etc. Objects of the present invention
The primary object of the present invention is to provide a system to obtain multi-channel current events based on non-in^'asive sensors.
An object of the present invention is to provide a system for obtaining muiti-channel current events wherein either single or multiple non-invasive sensors is/are used to measure current pulses from multiple current events originating from multiple channels.
Another object of the present invention is to provide a system for obtaining multi-channel current events that are temporally apart.
Yet another object of the present invention is to provide a system for obtaining multi-channel current events to reconstruct the waveform of current pulses that occur over multiple channels.
Still another object of the present invention is to provide a system for obtaining multi-channel current events for an event-based storage and packetized transmission of data corresponding to the multiple channels.
Further object of the present invention to provide a system for obtaining multi-channel current events having reduced system hardware requirements including number of sensors required, bit rate, reduced memory storage etc.
It is also an object of the present invention to provide a method for monitoring multiple current events in multiple channels by using single sensor/multiple sensors for multiple channels.

Summary of the invention
The present invention relates to a method and a system to obtain multichannel current events and to reconstruct the waveform of current pulses that occur over multiple channels. The present invention particularly relates to a system wherein single or multiple non-invasive sensors are used for monitoring multiple current events that are temporally apart and originating from multiple channels.
The system of the present invention comprises sensors, signal conditioning and data acquisition modules and a transmission format that can cater to the monitoring requirements of multiple current channels. This is achieved by using one sensor for many channels thus minimizing the total number of sensors required. The system also performs event based storage and packetised transmission of the acquired data corresponding to a predefined event. The system allows the defmition of the event to be flexible, like data crossing a certain threshold magnitude, occurrence at a certain time etc.
Further, in the present system, monitored pulsed currents are transmitted in a digital format through a system like a telemetry system to enable reconstruction of time-stamped current signatures. The system adopts Hall Effect sensors to convert the current pulse to voltage signals, signal conditioning and digitization circuitry to convert the data to digital format.
Some of the significant features of the present system include a provision for varying sample rates in the initial and later parts of the pulse, thresholding logic to detect 'significant' events in current channels and digital logic to time-stamp and communicate the data corresponding to various channels to a Central Controller for transmission to a receiver.
Event-based monitoring and packetised data transmission are further features of the system that enable simultaneous acquisition of large number of channels with considerable reduction in data rate.
The present invention further relates to a method to obtain multi-channel current events by means of single sensor or multiple sensors and to reconstruct said current events.

Brief Description of the accompanied drawings
Fig. 1 is a block diagram of the multi-channel current monitoring system
Fig. 2 is a view of a non-invasive current sensor s*'»owing the windings used to
measure the current passing through each channel corresponding to the number of
windings.
Fig. 3(a) & 3 (b) is a graphical sketch of current pulses in two separate lines.
Fig. 4 is an exemplary format in which the data corresponding to various channels
are stored in memory.
Figs. 5 and 6 depict a system flow diagram for obtaining multi-channel current
events.
Detailed description of the invention
The present invention provides a method and a system to acquire and reconstruct the waveform of current pulses that occur over multiple channels.
The invention is now explained with reference to the accompanied diagrams. Initially referring to Fig. 1, the system as shown, consists of 3 modules: Relay Module (RM), Current Sensing Module (CSM), AQUisition ELectronics Module (AQUEL) and. (CSM and RM are shown by dotted bounding box and all the other elements together constitute AQUEL).
Relay Module (RM): This block is optional to the system functionality. It consists of high current sensors (1) and relays (2) that can switch the currents to be measured (ON/OFF RELAY) - one each for prime and redundant channels. Thus the module switches and measures the total current drawn from each of the batteries and flowing through the CSMs.
Current Sensing Module (CSM): The CSM (3) comprises Hall Effect sensors and a signal conditioning circuit. A Single Hall Effect sensor is used for non-invasive monitoring of current flowing through the multiple lines. In the present invention, a total of 40 lines are adopted in an illustrative manner. The first 20 lines are designated as (3c) and the other 20 lines are designated as (3d). The sensors are mounted in the Current Sensing Module (CSM) for measuring the current pulses in the form of analog signals as received from a system (for instance, the Relay Module (RM), as shown in the Fig. 1, a charging / ignition

battery, a start-up circuit for electrical machinery etc.) The embodiment of incorporation of Hall Effect Sensors, in an illustrative manner is depicted in Fig. 2. The current carrying lines are wound on a rectangular core. A single sensor can carry several lines of varying current carrying capacity and turns. The sensor contains signal conditioning circuitry amplifies the signals and gives an output voltage that is proportional to the total current flowing through all the lines wound on it. The signal conditioning circuitry packaged along with the sensor consists of a signal amplifier that magnifies the amplitude of low-level signals produced by the Hal! Effect sensing element.
For instance, by referring to Sensor as depicted in Fig. 2, the sensor provides a full scale output of 5 V when lOA current flows through line (L3). Whereas, when 1 A flows through line (LI) whose full scale is 5 A, it gives an output of 5x1/5=1 V. For purposes of illustration 20 sensors each are shown in Fig. 1 for prime and redundant chains.
In CSM (3), dual redundancy is used for all the elements to ensure that malfunctioning of a single element does not lead to system failure. Thus for the current sensors two sets of components - one 'prime' (3a) and the other, 'redundant' (3b) are used to ensure that critical functionality is maintained in spite of failure of a single element.
The system interfaces (communicates the data) to a Central Control Unit (CCU) through either a wired link (as shown in the figure) or a wireless link. Dual redundancy is used for all the elements other than acquisition electronics to ensure that malfunction of a single element do not lead to system failure. Thus for the current sensors, relay module and CCU interface two sets of components - one 'prime' and the other, 'redundant' are used to ensure that critical functionality is maintained in spite of failure of a single element.
Current Sensors - Prime (3a) and Redundant (3b) sensors are housed in CSM. These sensors are Hall Effect Sensors used for non-invasive monitoring of current. The current carrying lines are wound on a rectangular core of the sensors (3a) and (3b). Now referring to Fig. 2 a single sensor can carry several lines of varying current carrying capacity and turns (A sampie illustration is given in Fig.

address is stepped sequentially so that the voltage output of each sensor becomes available to the succeeding stage at a predetermined sampling rate.
Analog to Digital Converters (ADCs): A plurality of Analog to Digital Converters (6) (ADCs) disposed to receive the scanned analog voltage signals from the analog multiplexers (4) and further to convert into digitized format.
The digitized sample size may vary from 4 bits to 16 bits i.e. from half a byte to two bytes, whereas 8 bits being a preferred option depending on the resolution (Resolution being the smallest change in current magnitude that can be detected by the system) and accuracy requirements of the data acquisition system. This depends on the sensitivity of components comprising the system as well as the sample size used in data converter. For example, an 8-bit system is capable of resolving 256 steps i.e. 19.5 mV in a 5 V full-scale. 'Accuracy' means the nearness or proximity of a measured value to the actual one. It depends on resolution as well as a host of other factors such as drift in component parameters, the calibration methods adopted etc.
Analog buffers: A plurality of Analog Buffers (5) is used to provide high input impedance to preceding MUX (4) outputs and low output impedance to succeeding analog to digital converters (6). Such an impedance matching is necessary for maximum voltage transfer from multiplexer (4) to analog-to-digital converters (6). Analog-to-digital converters (6) perform the sampling and digitization functions of the scanned sensor outputs. They generate the binary coded sample values corresponding to the sensor outputs and are controlled by the signals generated by the FPGA (7).
Field Programmable Gate Array (FPGA): An FPGA (7) acting as Write / Read / Decoder / Encoder Logic generates the digital control signals for sequentially scanning the sensor outputs, for sampling and digitization and detect an 'event' in a channel such as data crossing a certain preset threshold value, writing the coded sample values to appropriate blocks of Random Access Memory (RAM) (8) along with header information like time stamp and channel number and reading the data from RAM (8) on command from CCU (9). It also

generates the address for RAM (8) and handles the decoding of command from Central Control Unit (9) and encoding of reply to be sent to it.
The FPGA (7) detects a pre-defined event from the channel data and stores it on RAM (8) with suitable header information to enable subsequent independent reconstruction of the current waveform in each channel.
A Field Programmable Gate Array (FPGA) (7), acting as a processor is disposed in the system to receive the digitized samples and fiarther to process as per the predetermined factors selected from threshold logic, time of occurrence of the event etc. (A thresholding logic typically uses a digital comparator to detect the data sample going above a certain predetermined value. In FIG. 3(a), Al (15) is the threshold magnitude of current and it is A2 (19) in FIG. 3(b). The instant of current waveform crossing the threshold are indicated by the time stamps, Tl (17) and T2 (20) respectively in the figures. Thus the events are said to have begun at these time instants. Similarly the event definitions may be synchronized to an absolute time in this system or in another one. In this case the event is said to be initiated at such predetermined time irrespective of the current magnitude at that time). The generation of all the control signals required for digitization, setting the channel threshold values, data recording onto memory and transacting the data with controller are handled in a FPGA. Referring to Fig. 1, the decoding means for the command from a Central Control Unit (9) and encoding of the reply to be sent to it are also provided by the FPGA (7) if a digitally coded scheme of data communication is used in the link. Such a scheme may, for example, use bi-phase signaling format with the data bits framed by suitable synchronization and parity bits to ensure error-free communication between the systems
Random Access Memory (RAM): The memory (8) acting as storage means stores the data corresponding to the sensor channels along with the fime stamp information. The storage means is any known memory devices that can be used in any digitally implemented systems/processes. In the present invention, this storage means, a memory device, a random access memory device, is divided into banks - at least two in number, one for read and one for write and further into blocks - one for each channel. Each block gets written when an event is detected

in the corresponding sensor channel. The read operation is synchronized to com.mand from CCU (9). The overall memory, bank and block sizes are dependent on system requirements such as number of channels, sampling rate etc. The storage means consists of banks and blocks for Sioring processed digital data.
The digitized data samples are compared with a pre-determined threshold value. Each channel is allocated with a block of memory in the memory area RAM (8), whose length can vary from a few bytes to 10 Kbytes, with preferred storage area being 800 bytes, depending on the sampling rate and the expected maximum width of current pulse in that channel. (Sampling rate is the frequency at which samples of the current pulse are taken. The maximum width of current pulse is the longest duration over which the event is true, say; the current magnitude stays above a certain threshold value. For example in Fig. 3, the samples of current waveform are indicated by vertical dashed lines and Ts (14) is the time duration between any two of them. Then the sampling rate is fs=l/Ts. The threshold values are indicated by horizontal dotted lines as Al (15) for first channel in Fig. 3(a) and A2 (19) for second channel in Fig. 3(b). Tl (17) is the time instant of event start for first channel and T2 (20) that for second channel. Wl (16) is the pulse width from Tl (17) that the event is true for first channel in Fig. 3(a) and W2 (21) that from T2 (20) for second channel in Fig. 3(b). Thus the numbers of samples are Wlxfs and W2xfs for the first and second channels respectively). The memory is divided into two banks so that data recording and reading can proceed simultaneously without loss of data. The bank size may vary up to i Mbytes, preferably 32 Kbytes depending on the block size and the number of channels. An example for the format in which data corresponding to various channels are stored in memory is depicted in the form of a block diagram as shown in Fig. 4.
Here the data samples corresponding to each channel are stored in a block of memory along with header information such as times of event occurrence i.e. start of current pulse, number of samples above threshold etc. The time stamp bytes may correspond to the timer value i.e. the state of a timer counter implemented in the FPGA at the instant of occurrence of the event (Tl (17) and

T2 (20) in Fig. 3) with respect to an initial time reference such as a timer reset pulse. A number of such memory blocks (depending on number of channels) constitute a bank and a number of such banks (depending on the maximum number of events that can occur in a sensor within the time period for transmission of data) constitute the entire memory. (Bank number is the area of RAM where recording is done. Bank number is to be attached to the header during transmission of data only, not during storage of data into the RAM). Such a scheme of storing data ensures that all the relevant data required for reconstruction of pulsed events is preserved without loss in a compressed format that minimises the requirement of memory capacity.
Central Control Unit (CCU) Interface: As shown in Fig. 1, this block contains the electrical interface circuitry for the link to CCU (9). It typically consists of Pulse Transformer (10) and Line Receiver (11) on the input side to receive the command from CCU (9) and Line Driver (12) and Pulse Transformer (10) on the output side to send the reply to CCU (9). It is understood here that only the CCUl I/F (9) is shown in detail, CCU2 I/F (13) is similar in construction. As an illustration, a pair of CCU units (9 & 13) has been adapted in the system, of which one is primary and other being a redundant unit.
A Centra! Control Unit arranged to receive the processed digital signals from the processor sequentially at the reading rate up to 1Mbps, with a preferable reading rate of 4 Kbps depending on the bank size and the separation in time between the events. The separation is indicated by S (18) in Fig. 3 and becomes relevant if the current pulses shown in Fig. 3(a) and that in Fig. 3(b) occur on lines passing through the same sensor. The data is tagged with bank number, channel number, number of samples and time value to form a data packet that facilitates the reconstruction of current pulse waveform on a per channel basis.
A typical format of such a data packet or frame is shown below. Here the header information consists of (i) the bank number that helps to identify which of the memory banks is being read currently (ii) the channel number, that helps to identify which of the memory blocks is being read currently (iii) number of data samples of the particular channel in the current data frame and (iv) the time stamp

that indicates the start time of event occurrence in that channel. The header bytes are followed by the pre-specified number of data bytes. Such a format of communication data frame ensures faithful reconstruction of pulsed events with minimum requirements of signal bandwidth and data rate for the communication channel. The system also supports random reading with suitable header identification along with the data as explained.
controller unit should continue for a certain minimum time (depending on the reading rate and memory bank size) even after the occurrence of the last event to avoid data loss. (This is because there is a time lag between an event being written into memory and it being read by CCU. This latency in the worst case works out to the total memory capacity divided by the reading rate. Thus to ensure that the data corresponding to even the last event is transmitted properly, the communication with the CCU should be sustained at least one latency period after its occurrence).
The system for obtaining multi-channel current events for further reconstruction of the same is depicted in Figs, 5 and 6.
A method of measuring and obtaining current pulses in a multi channel environment by using a single non-invasive sensor for multiple channels
The method of the present invention permits the measurement of the total current flowing through all the channels and ftirther monitored using sensors of higher current rating. The current sensors work on the principle of Hall Effect and allow continuous monitoring of current. Due to Hall Effect the current to be measured (herein after called the 'primary current') creates a magnetic field around a semiconductor, carrying an excitation current. This magnetic field creates a voltage output and thereby a 'secondary current'. This secondary current is proportional to and balances the primary current. Multiple current carrying lines are accommodated on the same sensor by winding the current carrying wires

through it (as shown in Fig. 2). The full scale of each line is set by the number of w indings or turns of the corresponding wire that passes through the sensor. For example, if the sensor full scale is 10 A and the maximum amplitude of current in a line is 2 A, then 5 turns of the wire may be taken through the sensor. The sensor full scale may vary from lA to 200A and the line currents may vary from 0.1 A to 200 A. This indicates that the number of turns of a single line through a sensor may vary from 1 to 20 (5 being a typical value).
The full scale current amplitude may vary from 1 A to 200 A (5 A being a typical value) and is adjustable by using a suitable sensor configuration. The number of such channels that the system can cater to may vary from 2 to 100 (40 being a typical value) and the current pulse width over each channel may vary from 0.5 ms to 100 ms (40 ms being a typical value). The sampling period for the data acquisition can vary from 0.01 ms to 1 ms (0.05 ms being a typical value). The system also allows time tagging of the pulse events in various channels to a resolution that may vary from 0.01 ms to 1 ms (0.1 ms being a typical value). The transmission of the data thus acquired and stored in system memory may be event-based. The event is identified by the data crossing a specified threshold that may vary from 1% to 50% (10% being a typical value) of the full scale current amplitude for that channel. The transmission rate can be as low as 100 samples/s to 10 K samples/s (4 K samples/s being a typical value). This indicates a reduction in bit rate by as much as 1000 (10 being a typical value) that is made possible by event based transmission of data in multiple channels. This requires the events (current pulses) in a single channel to be temporally apart by 10 ms to several seconds (2 s being a typical value) depending on the transmission rate.
It may be noted that the current pulses in the various lines passing through a single sensor need to be temporally apart as described above for the event based reconstruction of each current pulse. If the pulses occur simultaneously, then the sensor output will indicate the total current flowing through that sensor.
The system is designed in such a manner as to allow flexibility in sampling rate during the various portions of current pulse. For example, the sample rate may be set at 18 KHz during the first 10 ms and at 6 KHz for the

latter 30 ms of a current pulse. This allows the various parts of a pulse to be reconstructed with different levels of detail or time resolution.
The threshold can be set digitally and may be made programmable on a per channel basis. When the data in a channel exceeds this threshold value the data samples are recorded in the form of blocks onto a Random Access Memory (RAM) (8) as shown in Fig. 1. In addition to the data the time of occurrence of the event is also recorded onto memory. This time is obtained by recording the timer value at the instant the rising edge of current pulse crosses the set threshold value.
The system may be designed to allow flexibility regarding the definition of 'event' also. For instance, a predefined time may be used to trigger the data recording instead of threshold detection. Here, the occurrence of event is defined with respect to timer crossing a preset value.
The system design may also incorporate an 'inhibition' period during which further recording of data in a channel is not allowed for a certain predefined time even if the event occurs in the channel. This 'inhibition' period may vary from tens of milliseconds to a few seconds depending on the guaranteed 'inactive' period for that channel. This avoids recording of 'spurious', unwanted events that may cause the useful event data to be over-written before it is read.
The flexibility of transmitting multiple events without loss is also accommodated by having multiple memory banks (instead of two). For example 4 memory banks will allow up to 4 events on a single channel. This allows the readins rate to be lower or the events to be closer in time.
Example A sample calculation for the separation of events in a single channel is shown below to illustrate how it depends on the various system parameters. The following parameters are assumed: Current amplitude, A = 5 A Resolution of measurement, R = 0.02 A
From these two parameters we can calculate the sample size using the formula, Sample size - Log2(A/R)

Hence, Sample size, S = log2(A/R) = log2(250) = 8 bits = 1 byte
(1)
Now assuming the following parameters,
Maximum pulse width to be measured, W = 40 ms
Sampling rate, K = 10 KHz
After obtaining the value of Sample size, S from the equation (1), now we can
calculate the Block length for a single channel by using the formula. Block
Length = W x K x S
where W - Maximum pulse width to be measured (Assumed)
K - Sampling Rate (Assumed)
S - Sample Size (Calculated from (1))
Hence, Block length for a single channel, B = WxKxS== 400 bytes (2)
Again assuming the following parameter,
Number of channels, N = 40
The value of the total memory bank size is calculated using the formula, Total Memory Bank Size = Block length (Calculated in (2)) x Number of channels (Assumed)
Hence, Total memory bank size, T = B x N = 16000 bytes (3)
Further assuming the Reading rate, X - 10 Kbytes/s
(This may correspond to 160 bytes being read in a major frame of duration 16 ms in the case of a conventional PCM telemetry system). The allowable time separation between events in a channel is calculated as follows
The allowable separation between events in a channel = T/X = 1.6 seconds Where, T - Total Memory Bank Size (Calculated in (3))
X - Reading Rate (Assumed) The above calculation assumes that only two memory banks are available - one of which is recorded while the other is being read.
Thus the system as described above allows flexible monitoring of pulsed currents in multiple channels. It makes use of the concepts of event-based monitoring and packetized data transmission that enable simultaneous acquisition

of large number of channels with considerable reduction in bit rate, when the data is to be transmitted to a central location.
Advantages
1. The present invention performs the function of multi-channel current
monitoring using a single sensor.
2. The present invention uses lesser bit rate and storage memory, due to the use of event-based storage and transmission system.
3. The system of the present invention is of reduced complexity as a result of reduction in hardware / bandwidth requirements.
4. The present invention allows definition of flexible events, like data crossing a certain threshold magnitude, occurrence at a certam time instant etc.
5. The present invention has the flexibility of transmitting multiple events without loss, by using multiple memory banks.
6. The present system allows for simultaneous reading from and writing into the m.emory, thus saving time and reducing the latency for data transmission.
7. The system of the present invention has applications in monitoring pulsed current in battery charging and spark ignition systems of automobiles, power switching systems, turn on/off systems for electric machinery like motors and generators, electric power transmission networks, characterisation / test systems for power semiconductor devices / circuit in electronic industry, performance monitoring systems for industrial / chemical process control, safety systems such as lightning arrestors, pyro initiated event sequencing systems etc.

We claim
1. A system for obtaining multi-channel current events for reconstruction and monitoring, comprising: non-invasive sensors with a plurality of input current lines wound on the sensors to provide an output of voltage channels with voltage pulse events, a plurality of analog multiplexers with address bus to receive the voltage channels, an ON/OFF enabling switch on each analog multiplexer to enable/disable the corresponding analog multiplexer, a digital processor with a clock to scan the address bus of *said analog multiplexer to enable the switch and to select the desired scanned voltage channel carrying voltage pulsed events, a plurality of analog to digital converters for converting said voltage pulsed events of the selected voltage channel into digital data, said digital processor to sample, detect and time-stamp the occurrence of pulsed events in said voltage channel that occur at a predetermined triggering instant or a threshold vaLie of voltage of said voltage channel, and to trigger the recording of data, a storage means for storing the triggered digital data, and a central control unit for receiving the digital data for reconstruction to original analog signals.
2. The system as claimed in claim 1, wherein a single non-invasive and/or multiple sensors are used for multiple current lines with the current pulses in the various lines passing through a single sensor being separated in time.
3. The system as claimed in claim 2, wherein the non-invasive sensor is a Hall Effect sensor.
4. The system as claimed in claim 1, wherein the number of turns of each of the plurality of current lines on the sensor varies from 1-20.
5. The system as claimed in claim 4, said plurality of current lines is based on the full scale amplitude of current pulses, pulse width and time separation instant.
6. The system as claimed in claim 5, wherein the full-scale current amplitude is in the range of 5A-200A.
7. The system as claimed in claim 1, wherein the number of voltage channels is in the range of 2-100, preferably 40 channels.

8. The system as claimed in claim 1, wherein the storage means consisting of banks and blocks for storing processed digital data.
9. A method for obtaining multi-channel current events for reconstruction and monitoring, said method comprising the steps of: sensing current pulses of multiple input current lines by means of non-invasive sensors to generate voltage channels, sampling and scanning said voltage channels to select a single voltage channel, converting voltage signals of said single voltage channel into digitized data by means of Analog to Digital Converters, storing a pre-determined digitized voltage signal level as a threshold value to record the digitized voltage signals in a storage memory along with header information consisting of the number of the selected channel and number of samples of the voltage signals of the selected channel, time-stamping of the recorded events, said processor further adapted to effect an inhibition period thereby preventing recording of the data, and transmitting to Central Control Unit in the form of a data packet for reconstruction into analog signals.
10. A method for obtaining multi-channel current events for reconstruction and monitoring as claimed in claim 9, wherein the storage of a pre-determined digitized voltage signal is performed by storing triggering instant of occurrence of digitized voltage signal and recording the occurrence of digitized data at said pre-determined triggering instant of occurrence.
11. The method as claimed in claims 9, wherein the rate of sampling is in the range 1 KHz - 100 KHz, preferably 20 KHz.
12. The method as claimed in claims 9, wherein the width of the current pulse over each current line is in the range of 0.5-100 ms, preferably 40ms.
13. The method as claimed in claims 9, wherein the period of sampling is in the range of 0.01-1 ms, preferably 0.05 ms.
14. The method as claimed in claims 9, wherein the rate of scanning is in the range of 2KHz to 10 MHz, preferably 800 KHz.
15. The method as claimed in claim 9, wherein the threshold value is predetermined in the range of 1-50% of full-scab current amplitude of input current lines.

16. The method as claimed in claim 9, wherein the full-scale current amplitude is
in the range of 5A-200A.
17. The method as claimed in claims 9, wherein the number of samples is the
product of rate of sampling and width of the current pulses.
18. The method as claimed in claims 9, wherein the time stamping of the pulse
events in various channels is done to a resolution in the range of 0.01-1 ms,
preferably 0.1 ms.
19. The method as claimed in claims 9, wherein a/' inhibition period is used to
prevent recording of data in a channel even when the event occurs to prevent
spurious and unwanted events that may cause the useful data to be over
written before they are read.
20. The method as claimed in claims 9, wherein the transmission rate of the data
is in the range of 100 - 10 K samples/s, preferably 4 K samples/s.
21. The method as claimed in claims 9, wherein the data packet consisting of
with bank number, channel number, number of samples and time stamp as
header information along with data.
22. The method as claimed in claim 10, wherein the pre-determined triggering
instant in a single channel is in the range of 10ms to 10 sees, preferably 2
sees to trigger the data recording.

Documents:

097-che-2004-abstract.pdf

097-che-2004-claims filed.pdf

097-che-2004-claims granted.pdf

097-che-2004-correspondnece-others.pdf

097-che-2004-correspondnece-po.pdf

097-che-2004-description(complete) filed.pdf

097-che-2004-description(complete) granted.pdf

097-che-2004-drawings.pdf

097-che-2004-form 1.pdf

097-che-2004-form 19.pdf

097-che-2004-form 26.pdf

097-che-2004-form 3.pdf

097-che-2004-form 5.pdf

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Patent Number

220157

Indian Patent Application Number

97/CHE/2004

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

16-May-2008

Date of Filing

09-Feb-2004

Name of Patentee

INDIAN SPACE RESEARCH ORGANISATION (ISRO)

Applicant Address

HEADQUARTERS, ANTARIKSH BHAVAN, NEW B.E.L ROAD, BANGALORE 560 094,

Inventors:

#	Inventor's Name	Inventor's Address
1	SREEKUMAR SANKARATTIL	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
2	PADMANABHA RAO VINOD	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
3	ARYANAYAKIPURAM RAMANATHAN KRISHNAN	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
4	DAMODARAN KOLLAMPARAMBIL	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
5	SREELAL SREEDHARAN PILLAI	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
6	PADMA PADMANABHAN	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
7	SREEKUMAR SANKARATTIL	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
8	PADMANABHA RAO VINOD	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
9	ARYANAYAKIPURAM RAMANATHAN KRISHNAN	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
10	DAMODARAN KOLLAMPARAMBIL	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
11	SREELAL SREEDHARAN PILLAI	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
12	PADMA PADMANABHAN	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
13	SREEKUMAR SANKARATTIL	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
14	PADMANABHA RAO VINOD	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
15	ARYANAYAKIPURAM RAMANATHAN KRISHNAN	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
16	DAMODARAN KOLLAMPARAMBIL	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
17	SREELAL SREEDHARAN PILLAI	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,
18	PADMA PADMANABHAN	VIKRAM SARABHAI SPACE CENTRE, INDIAN SPACE RESEARCH ORGANISATION (ISRO), TRIVANDRUM, KERALA 695 022,

PCT International Classification Number

G01R /00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA