# US 11,994,545 B2 · DC resistance measurement contact checking via alternating current high frequency injection > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,994,545 B2 - Document ID: US11994545B2 - Status: Granted - Kind: B2 - Application number: 17/728,377 - Filed: 2022-04-25 - Published: 2022-11-17 - Granted: 2024-05-28 - Earliest claimed: 2021-05-11 - Assignees: National Instruments Corporation - Applicants: National Instruments Corporation - Inventors: Chin-Hong Cheah; Tatt-Wee Oong; Eric Hartner - Web page: https://patentgrep.com/patent/US11994545B2 ## CPC - G01R 27/16: Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line - G01R 31/2879: {related to electrical aspects, e.g. to voltage or current supply or stimuli or to electrical loads} - G01R 31/31924: {Voltage or current aspects, e.g. driver, receiver} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract A test system may be used for obtaining accurate remote sense voltage and/or current values. A measurement instrument may provide a regulated stimulus signal to a device under test (DUT) and measure a DUT signal developed at least partially in response to the stimulus signal. A test circuit may superimpose a test signal over the stimulus signal to cause the DUT signal to be developed further in response to the test signal. The DUT signal may be used to derive a resistance of the path that couples the measurement instrument to the DUT. The measurement instrument may include a source measure unit, the stimulus signal may be a regulated voltage, and the DUT signal may be a sense voltage. The harmonics of the DUT signal may be analyzed to determine a correlation between an amplitude of a measured fundamental frequency of the DUT signal and the resistance of the path. ## Claims ### Claim 1 A system for measuring cable resistance, the system comprising: a measurement circuit configured to provide a stimulus signal to a device under test (DUT) and measure a DUT signal developed responsive to at least the stimulus signal; and a contact check circuit configured to superimpose a test signal over the stimulus signal to cause the DUT signal to be developed responsive additionally to the test signal; wherein the measurement circuit is further configured to derive respective resistances of one or more paths coupling the measurement circuit to the DUT, based at least on the DUT signal. ### Claim 2 (depends on 1) The system of claim 1, wherein the measurement circuit comprises a source measure unit. ### Claim 3 (depends on 1) The system of claim 1, wherein the stimulus signal is a regulated voltage and the DUT signal is a sense voltage. ### Claim 4 (depends on 1) The system of claim 1, wherein the test signal comprises square waves. ### Claim 5 (depends on 1) The system of claim 1, wherein the test signal has a specified frequency. ### Claim 6 (depends on 1) The system of claim 1, wherein the measurement circuit is further configured to analyze harmonics of the DUT signal to determine a correlation between an amplitude of a measured fundamental frequency of the DUT signal and the respective resistances of the one or more paths. ### Claim 7 (depends on 1) The system of claim 1, wherein the contact check circuit comprises a resistive-capacitive (RC) network coupling to the respective resistances of the one or more paths. ### Claim 8 (depends on 1) The system of claim 1, wherein the one or more paths comprise cables. ### Claim 9 (depends on 1) The system of claim 1, wherein the contact check circuit comprises a guard circuit configured to prevent leakage current in the one or more paths during measurement of the DUT signal when the test signal is not superimposed over the stimulus signal. ### Claim 10 A system for performing accurate voltage, current, and load measurements, the system comprising: a measurement device configured to: couple to a device under test (DUT) via one or more cables; provide a stimulus signal the DUT; and measure a DUT signal, wherein the DUT signal is developed responsive to at least the stimulus signal; and a contact check circuit configured to superimpose a test signal over the stimulus signal to cause the DUT signal to be developed responsive additionally to the test signal; wherein the measurement device is further configured to derive a resistance of the one or more cables based at least on the DUT signal. ### Claim 11 (depends on 10) The system of claim 10, wherein the stimulus signal is a regulated voltage and the DUT signal is a sense voltage. ### Claim 12 (depends on 10) The system of claim 10, wherein the test signal comprises square waves having a specified frequency. ### Claim 13 (depends on 10) The system of claim 10, wherein the measurement device is further configured to analyze harmonics of the DUT signal to determine a correlation between an amplitude of a measured fundamental frequency of the DUT signal and the resistance of the one or more cables. ### Claim 14 (depends on 10) The system of claim 10, wherein the contact check circuit comprises a resistive-capacitive (RC) network coupling to the one or more cables. ### Claim 15 (depends on 10) The system of claim 10, wherein the contact check circuit comprises a guard circuit configured to prevent leakage current in the one or more paths during measurement of the DUT signal when the test signal is not superimposed over the stimulus signal. ### Claim 16 A contact check measurement circuit comprising: a set of inputs configured to receive respective input signals; circuitry configured to generate test signals corresponding to the respective input signals; a set of outputs configured to superimpose the test signals over a stimulus signal provided to a device under test (DUT); and processing circuitry configured to determine a resistance of one or more coupling paths to the DUT based at least on a DUT signal, wherein the DUT signal is developed responsive to the stimulus signal and the test signals. ### Claim 17 (depends on 16) The contact check measurement circuit of claim 16, further comprising: a guard circuit configured to prevent leakage current in the one or more coupling paths during measurement of the DUT signal when the test signals are not superimposed over the stimulus signal. ### Claim 18 (depends on 16) The contact check measurement circuit of claim 16, wherein the test signals comprise square waves having a specified frequency. ### Claim 19 (depends on 16) The contact check measurement circuit of claim 16, wherein the stimulus signal is a regulated voltage and the DUT signal is a sense voltage. ### Claim 20 (depends on 16) The contact check measurement circuit of claim 16, further comprising: a resistive-capacitive (RC) network coupling to the one or more coupling paths.