# US 9,182,256 B2 · Process variable transmitter with two-wire process control loop diagnostics > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,182,256 B2 - Document ID: US9182256B2 - Status: Granted - Kind: B2 - Application number: 12/832,341 - Filed: 2010-07-08 - Published: 2011-01-13 - Granted: 2015-11-10 - Earliest claimed: 2009-07-09 - Assignees: Rosemount Inc. - Applicants: David L. Wehrs; Gregory J. LeCuyer; Jessica Lo; Steven J. McCoy; Brian L. Westfield - Inventors: David L. Wehrs; Gregory J. LeCuyer; Jessica Lo; Steven J. McCoy; Brian L. Westfield - Web page: https://patentgrep.com/patent/US9182256B2 ## CPC - G01D 21/00: Measuring or testing not otherwise provided for - G05B 19/0423: {Input/output} - G05B 2219/24069: Diagnostic - 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 - G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G) ## Abstract A two-wire process variable transmitter for use in an industrial process, including a process variable sensor configured to sense a process variable of a fluid of the industrial process. Output circuitry is configured to provide an output on a two-wire process control loop which is related to the sensed process variable. Loop current measurement circuitry measures a loop current flowing through the two-wire process control loop and terminal voltage measurement circuitry measures a voltage related to a terminal voltage of the process variable transmitter. The terminal voltage can be a voltage measured across an electrical connection of the two-wire process variable transmitter to the two-wire process control loop. Input circuitry is configured to receive a diagnostic command from the two-wire process control loop. A microprocessor configured to perform loop diagnostics on the two-wire process control loop based upon the measured loop current and terminal voltage in response to receipt of a diagnostic command from the two-wire process control loop. ## Claims ### Claim 1 A two-wire process variable transmitter for use in an industrial process, comprising: terminals configured to couple to a two-wire process control loop; a process variable sensor configured to sense a process variable of a process fluid of the industrial process; output circuitry coupled to the terminals configured to provide an output on the two-wire process control loop which is related to the sensed process variable; current measurement circuitry coupled to the terminals configured to measure a loop readback current flowing through the two-wire process control loop and a shunt current; terminal voltage measurement circuitry coupled to the terminals configured to measure a voltage related to a terminal voltage of the process variable transmitter, the terminal voltage comprising a voltage measured across the terminals of the two-wire process variable transmitter; a microprocessor configured to perform loop diagnostics on the two-wire process control loop based upon the measured loop readback current, the measured shunt current and terminal voltage and calculate a loop resistance based upon a difference in the measured terminal voltage measured with two different current levels flowing through the two-wire process control loop and a difference in the measured loop readback current with the two different current levels flowing through the two-wire process control loop. ### Claim 2 (depends on 1) The two-wire process variable transmitter of claim 1 wherein the diagnostic command causes the microprocessor to perform a loop characterization. ### Claim 3 (depends on 1) The two-wire process variable transmitter of claim 1 wherein the diagnostics include a determination of a voltage of a power supply of the two-wire process control loop. ### Claim 4 (depends on 1) The two-wire process variable transmitter of claim 1 wherein the diagnostics include performing a preliminary diagnostic check. ### Claim 5 (depends on 1) The two-wire process variable transmitter of claim 1 wherein the diagnostics include determining a baseline diagnostic value. ### Claim 6 (depends on 1) The two-wire process variable transmitter of claim 1 wherein the diagnostics include determining a quiescent current value. ### Claim 7 (depends on 1) The two-wire process variable transmitter of claim 1 including a temperature sensor and wherein the diagnostics are compensated based upon a sensed temperature. ### Claim 8 (depends on 1) The two-wire process variable transmitter of claim 1 wherein measurement of the loop readback current and terminal voltage are performed in synchronization. ### Claim 9 (depends on 1) The two-wire process variable transmitter of claim 1 wherein the diagnostic command is in accordance with an Electronic Device Description Language (EDDL). ### Claim 10 (depends on 1) The two-wire process variable transmitter of claim 1 including: input circuitry coupled to the terminals configured to receive a diagnostic command from the two-wire process control loop; and wherein the microprocessor is configured to perform loop diagnostics in response to a diagnostic command received from the two-wire process control loop. ### Claim 11 A method of performing diagnostics in a two-wire process variable transmitter of an industrial process, comprising: coupling terminals of the two-wire process variable transmitter to a two-wire process control loop; sensing a process variable of a process fluid of the industrial process; providing an output on the two-wire process control loop which is related to the sensed process variable; coupling current measurement circuitry to the two-wire process control loop, the current measurement circuitry configured to measure a loop readback current flowing through the terminals of the two-wire process variable transmitter and a shunt current; coupling terminal voltage measurement circuitry to the terminals of the two-wire process variable transmitter, the terminal voltage measurement circuitry configured to measure a terminal voltage across the terminals of the two-wire process variable transmitter; and performing diagnostics on the two-wire process control loop, the diagnostics performed using the measured loop readback current, the measured shunt current, and the measured terminal voltage, the diagnostics including calculating a loop resistance based upon a difference in the measured terminal voltage measured with two different current levels flowing through the two-wire process control loop and a different in the measured loop readback current with the two different current levels flowing through the two-wire process control loop. ### Claim 12 (depends on 11) The method of claim 11 wherein the diagnostics include a determining of a voltage of a power supply of the two-wire process control loop. ### Claim 13 (depends on 11) The method of claim 11 wherein the diagnostics include performing a preliminary diagnostics check. ### Claim 14 (depends on 11) The method of claim 11 wherein the diagnostics include determining a baseline diagnostic value. ### Claim 15 (depends on 11) The method of claim 11 wherein the diagnostics include determining a quiescent current value. ### Claim 16 (depends on 11) The method of claim 11 including sensing a temperature and wherein the diagnostics are compensated based upon the sensed temperature. ### Claim 17 (depends on 11) The method of claim 11 wherein measurement of the loop readback current and terminal voltage are performed in synchronization. ### Claim 18 (depends on 11) The method of claim 11 wherein the diagnostic command is in accordance with an Electronic Device Description Language (EDDL). ### Claim 19 (depends on 11) The method of claim 11 wherein characterizing includes measuring baseline values for loop resistance and loop power supply voltage. ### Claim 20 (depends on 11) The method of claim 11 wherein the step of performing diagnostics is in response to receiving a diagnostic command from the two-wire process control loop.