# US 10,374,597 B2 · Circuit state sensing > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,374,597 B2 - Document ID: US10374597B2 - Status: Granted - Kind: B2 - Application number: 15/304,303 - Filed: 2015-04-14 - Published: 2017-02-09 - Granted: 2019-08-06 - Earliest claimed: 2014-04-15 - Assignees: BAE SYSTEMS plc - Applicants: BAE SYSTEMS plc - Inventors: David Christopher D'Oyly-Watkins - Web page: https://patentgrep.com/patent/US10374597B2 ## CPC - H03K 17/18: Modifications for indicating state of switch - G01R 31/2621: {for testing field effect transistors, i.e. FET's} - G01R 31/3277: {of low voltage devices, e.g. domestic or industrial devices, such as motor protections, relays, rotation switches} - G01R 31/62: Testing of transformers - H01F 27/28: Coils; Windings; Conductive connections - H01F 27/34: Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields - G01R 31/72: Testing of electric windings (testing of transformers G01R31/62) - H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M) - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES ## Abstract A circuit state sensing device (100) includes a transformer (102) having a primary coil (104A) and a secondary coil (104B). In use, the secondary coil is connected to a target circuit (106) for which a state is to be sensed. The device further includes a measuring arrangement (112, 122) configured to take a measurement relating to impedance at the primary coil, and a processing arrangement (122) configured to process the impedance measurement to determine a state of the target circuit. ## Claims ### Claim 1 A circuit state sensing device, comprising: a plurality of transformers each having a primary coil and a secondary coil, in use, each of the secondary coils being connected to an associated one of a plurality of target circuits for which a state is to be sensed; a measuring arrangement configured to take measurements relating to impedance at the primary coil of each of the transformers; and a processing arrangement configured to process the measurement to determine a state of each of the target circuits. ### Claim 2 (depends on 1) The device according to claim 1, further including a current providing arrangement configured to selectively provide a current to the primary coil of at least one of the transformers. ### Claim 3 (depends on 2) The device according to claim 2, further including a resetting arrangement configured to reset residual flux of at least one of the transformers. ### Claim 4 (depends on 3) The device according to claim 3, wherein the measuring arrangement includes an arrangement configured to measure a time taken for the current provided to the primary coil of a said transformer by the current providing arrangement to reach a predetermined current value. ### Claim 5 (depends on 4) The device according to claim 4, wherein the processing arrangement includes: a comparison arrangement configured to compare the time measured by the measuring arrangement with a stored time value, and an output arrangement configured to generate an output signal based on a result provided by the comparison arrangement. ### Claim 6 (depends on 5) The device according to claim 5, wherein the stored time value represents time taken for the current at the primary coil of a said transformer to reach the predetermined current value when a rate of change of the current at the primary coil is effectively limited by a current sense resistor connected to the primary coil of said transformer. ### Claim 7 (depends on 1) The device according to claim 1, where, in use, at least one of the target circuits includes a switch, wherein the device is configured to sense an open/closed state of the switch. ### Claim 8 (depends on 1) The device according to claim 1, where, in use, at least one of the target circuits includes a voltage source, wherein the device is configured to sense a voltage state of the respective target circuit(s). ### Claim 9 (depends on 1) The device according to claim 1, further including: a plurality of current providing arrangements each configured to selectively provide a current to the primary coil of an associated one of the transformers; a plurality of resetting arrangements each configured to reset residual flux of an associated one of the transformers; wherein the measuring arrangement includes an arrangement configured to measure a time taken for the current provided to the primary coil of a said transformer by the associated current providing arrangement to reach a predetermined current value. ### Claim 10 (depends on 9) The device according to claim 9, wherein the plurality of current providing arrangements include a plurality of current control switches arranged as an analogue multiplexer. ### Claim 11 (depends on 1) The device according to claim 1, where, in use, at least one of the target circuits includes a voltage source and a current limit resistor, wherein a value of the current limit resistor is chosen to set a current through the secondary coil of the respective transformer at a value sufficient to ensure saturation of a core of the respective transformer when a minimum expected voltage is applied to the respective target circuit. ### Claim 12 (depends on 1) The device according to claim 1, wherein at least one of the target circuits includes a power switch that, in use, is connected to the secondary coil of the respective transformer via at least one isolation capacitor, and wherein the device is configured to sense the state of the power switch. ### Claim 13 (depends on 2) The device according to claim 2, wherein the device is configured to monitor states of a plurality of FET switches that control power from a source to a safety critical load, each said FET switch being associated with a respective said transformer and, in use, the device monitors states of the FET switches by using the current providing arrangement to selectively provide a current to the primary coil of one or more of the transformers in a sequence, and checking if the state of each said FET switch corresponds to an expected state based on the current provided by the sequence. ### Claim 14 A method of sensing a state of a circuit, the method including: providing a plurality of transformers each having a primary coil and a secondary coil; connecting each of the secondary coils, in use, to an associated one of a plurality of target circuits for which a state is to be sensed; taking a measurement relating to impedance at each of the primary coils; and processing the impedance measurement to determine a state of each of the target circuits. ### Claim 15 A circuit state sensing device, comprising: a plurality of transformers each having a primary coil and a secondary coil, in use, each of the secondary coils being connected to an associated one of a plurality of target circuits for which a state is to be sensed; a switch circuit connected in series with the primary coil of each of the target circuits; and a controller circuit configured to control the switch circuit and take a measurement relating to impedance at the primary coil of each of the transformers when the switch circuit is engaged so as to allow current flow through the primary coil of each of the transformers, the controller circuit further configured to process the measurement to determine a state of each of the target circuits. ### Claim 16 (depends on 15) The device according to claim 15, further comprising at least one of: a power supply operatively coupled to at least one of the transformers so as to provide a current to the primary coil of each respective transformer; and a fly-back diode connected across the primary coil of the at least one of the transformers. ### Claim 17 (depends on 15) The device according to claim 15, further comprising: a current sense resistor connected to the primary coil of at least one of the transformers; wherein the controller circuit is a microcontroller configured for measuring a time taken for current provided to the primary coil of the respective transformer(s) to reach a predetermined current value, the microcontroller including a comparator circuit configured to compare the measured time with a pre-established time value, and to generate an output signal based on the comparison, wherein the pre-established time value represents time taken for the current at the primary coil of the respective transformer(s) to reach the predetermined current value when a rate of change of the current at the primary coil of the respective transformer(s) is effectively limited by the current sense resistor connected to the primary coil of the respective transformer(s). ### Claim 18 (depends on 15) The device according to claim 15, further comprising: a current sense circuit connected to the primary coil of at least one of the transformers; wherein the controller circuit is configured for measuring a time taken for current provided to the primary coil of the respective transformer(s) to reach a predetermined current value, the controller circuit including a comparator circuit configured to compare the measured time with a pre-established time value, and to generate an output signal based on the comparison, wherein the pre-established time value represents time taken for the current at the primary coil of the respective transformer(s) to reach the predetermined current value when a rate of change of the current at the primary coil of the respective transformer(s) is effectively limited by the current sense circuit connected to the primary coil of the respective transformer(s). ### Claim 19 (depends on 15) The device according to claim 15, where, in use, at least one of the target circuits includes at least one of: a current control switch, wherein the device is configured to sense an open/closed state of the current control switch; a voltage source, wherein the device is configured to sense a voltage state of the target circuit; a voltage source and a current limit resistor, wherein a value of the current limit resistor is chosen to set a current through the secondary coil of at least one of the transformers at a value sufficient to ensure saturation of a core of the respective transformer(s) when a minimum expected voltage is applied to the respective target circuit(s); a power switch, wherein the device is configured to sense a state of the power switch wherein, in use, the power switch is connected to the secondary coil of the respective transformer(s) via at least one isolation capacitor; and a FET switch that controls power from a source to a safety critical load, wherein the device is configured to monitor a state of the FET switch by selectively providing a current to the primary coil of the respective transformer(s), and to check via the controller circuit whether a state of said FET switch corresponds to an expected state based on the current provided to the primary coil of the respective transformer(s).