# US 2013/0154660 A1 · System and method for ground fault detection and fault type evaluation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0154660 A1 - Document ID: US20130154660A1 - Status: Published application - Kind: A1 - Application number: 13/648,242 - Filed: 2012-10-09 - Published: 2013-06-20 - Earliest claimed: 2011-12-19 - Assignees: Tyco Safety Products Canada Ltd. - Inventors: Andrei Bucsa; Stephen D. W. Fosty; Aurel Cojocaru - Web page: https://patentgrep.com/patent/US20130154660A1 ## CPC - G01R 23/02: Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage - G01R 19/00: Arrangements for measuring currents or voltages or for indicating presence or sign thereof (G01R5/00 takes precedence; for measuring bioelectric currents or voltages A61B5/24) - G06F 17/00: Digital computing or data processing equipment or methods, specially adapted for specific functions (information retrieval, database structures or file system structures therefor G06F16/00) - H02H 3/087: for DC applications - H02J 7/865: {Battery or charger load switching, e.g. concurrent charging and load supply (H02J7/50 takes precedence)} - F16H 59/105: {consisting of electrical switches or sensors} - G01B 7/003: {for measuring position, not involving coordinate determination (coordinate measuring G01B7/004)} - G01B 7/14: for measuring distance or clearance between spaced objects or spaced apertures (G01B7/30 takes precedence) - G01D 5/2457: {Incremental encoders having reference marks} - H02H 3/06: with automatic reconnection - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) - H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H) - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - F16H: GEARING - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS - G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR ## Abstract The embodiments disclose a circuit for detecting and determining a type of ground fault in a security system. An operational amplifier (OA) having positive and negative inputs and an output may receive AC input signals having different frequencies, f1 and f2 at a positive input and provide an AC output signal at the output. An OA feedback loop may comprise a ground fault equivalent impedance connected at the OA negative input and a feedback resistor connected between the OA output and the OA negative input. A rectifier may convert the AC output signal to a DC signal and a filter to obtain a steady DC voltage from the rectified DC signal. A steady DC voltage for two different AC input signals may be obtained and converted to a relative voltage with respect to a constant input voltage amplitude. The relative voltages may be compared to detect and determine a type of ground fault condition. ## Claims ### Claim 1 A method of determining a type of ground fault condition in a circuit comprising: applying a first and a second AC input signal having a first and a second frequency (f1 and f2) and a constant voltage level to a positive input of an operational amplifier (OA) to obtain a first and a second AC output signal; applying a first and a second feedback signal to a negative input of the OA, the first and second feedback signals derived from the first and second AC output signals coupled to a ground path impedance; rectifying the first and the second AC output signals to obtain first and second DC signals; filtering the rectified first and second DC signals to obtain first and second steady DC voltages; determining a first and a second relative voltage by subtracting the constant voltage level from the first and second steady DC voltages; determining a ratio of the second relative voltage to the first relative voltage; and characterizing a type of ground fault according to the ratio. ### Claim 2 (depends on 1) The method of claim 1, wherein the first frequency (f1) and second frequency (f2) are in a ratio of n:1. ### Claim 3 (depends on 1) The method of claim 1, the ground path impedance comprising a feedback resistance (RFB) coupled with a ground impedance (ZG). ### Claim 4 (depends on 2) The method of claim 2, the characterizing a type of ground fault according to the ratio further comprising characterizing the ground fault as a pure resistive fault when the ratio is 1. ### Claim 5 (depends on 1) The method of claim 1, the characterizing a type of ground fault according to the ratio further comprising characterizing the ground fault as a reactive fault when the ratio is greater than 1 and less than n. ### Claim 6 (depends on 1) The method of claim 1, the characterizing a type of ground fault according to the ratio further comprising characterizing the ground fault as a pure reactive fault when the ratio is n. ### Claim 7 (depends on 1) The method of claim 1, further comprising: measuring a voltage amplitude level of the output of the OA when no input signal is applied to the positive input of the OA; and determining there is an AC ground fault when there is a non-zero voltage amplitude level at the output of the OA. ### Claim 8 (depends on 1) The method of claim 1, further comprising creating an alert notification to notify of the existence of the ground fault condition, the alert notification sent to one of a control panel, a keypad, and a remote monitoring location. ### Claim 9 (depends on 8) The method of claim 8, the alert notification comprising a sound emitted in a particular pattern to indicate the type of ground fault condition. ### Claim 10 (depends on 8) The method of claim 8, the alert notification comprising a light blinking in a particular pattern to indicate the type of ground fault condition. ### Claim 11 A ground fault detection circuit comprising: an AC function generator configured to generate at least two separate AC input signals having a constant voltage level and different frequencies, f1 and f2 in a ratio of n:1; an operational amplifier (OA) having positive and negative inputs and an output, the OA configured to receive the AC input signals at the positive input and provide an AC output signal; an OA feedback loop in which earth ground is coupled at the negative input of the OA with the AC output signal that is coupled to the negative input of the OA through a feedback resistor; a rectifier configured to receive the AC output signal and convert it to a DC signal; and a filter configured to receive the rectified DC signal and output a steady DC voltage. ### Claim 12 (depends on 11) The ground fault detection circuit of claim 11, the AC function generator comprising a direct digital synthesis (DDS) sine wave generator. ### Claim 13 (depends on 11) The ground fault detection circuit of claim 11, wherein: a first steady DC voltage (vout1) is recorded when the first AC input signal is applied to the OA positive input; a first relative voltage is determined by subtracting the constant voltage level from the first steady DC voltage; a second steady DC voltage (vout2) is recorded when the second AC input signal is applied to the OA positive input; a second relative voltage is determined by subtracting the constant voltage level from the second steady DC voltage; a ratio between second relative voltage and first relative voltage (vrel—2/vrel—1) is determined; and a ground fault type is determined based on the ratio. ### Claim 14 (depends on 13) The ground fault detection circuit of claim 13, wherein the ground fault type is characterized as pure resistive when the ratio is 1. ### Claim 15 (depends on 13) The ground fault detection circuit of claim 13, wherein the ground fault type is characterized as reactive when the ratio is greater than 1 and less than n. ### Claim 16 (depends on 13) The ground fault detection circuit of claim 13, wherein the ground fault type is characterized as pure reactive when the ratio is n. ### Claim 17 (depends on 11) The ground fault detection circuit of claim 11, wherein an AC ground fault is determined when a non-zero gain at the output of the OA is detected when no input signal is applied to the OA positive input. ### Claim 18 (depends on 17) The ground fault detection circuit of claim 17, further comprising creating an alert notification to notify of the existence of the ground fault condition, the alert notification sent to one of a control panel, a keypad, and a remote monitoring location associated with a security system. ### Claim 19 (depends on 13) The ground fault detection circuit of claim 13, further comprising creating an alert notification to notify of the existence of the ground fault condition, the alert notification sent to one of a control panel, a keypad, and a remote monitoring location associated with a security system.