# US 2005/0168343 A1 · Process control loop current verification > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2005/0168343 A1 - Document ID: US20050168343A1 - Status: Published application - Kind: A1 - Application number: 11/095,386 - Filed: 2005-03-31 - Published: 2005-08-04 - Earliest claimed: 2003-08-07 - Assignees: Rosemount Inc. - Inventors: Randy Longsdorf; Garrie Huisenga; James Johnson - Web page: https://patentgrep.com/patent/US20050168343A1 ## CPC - G01R 19/2509: {Details concerning sampling, digitizing or waveform capturing} - G05B 19/0425: {Safety, monitoring} - G08C 19/02: in which the signal transmitted is magnitude of current or voltage (G08C19/36, G08C19/38 take precedence) - G05B 2219/25189: Current mode sensor I-O, current loop, 40-mA loop instead of voltage - G05B 2219/25428: Field device - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - 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) - G08C: TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS (fluid pressure transmitting systems F15B; mechanical means for transferring the output of a sensing member into a different variable G01D5/00; mechanical control systems G05G) ## Abstract A process device is configured for coupling to a two wire process control loop. Loop current output circuitry is configured to apply an output current to the two wire process control loop. Loop current verification circuitry is coupled to the two wire process control loop and configured to detect errors in the applied output current. At least a portion of the loop current verification circuitry is independent from the loop current output circuitry. ## Claims ### Claim 1 A process device, comprising; loop current output circuitry configured to apply an output current to a two wire process control loop; and loop current verification circuitry coupled to the two wire process control loop to detect errors in the applied output current, wherein at least a portion of the loop current verification circuitry is independent from the loop current output circuitry. ### Claim 2 (depends on 1) The apparatus of claim 1 wherein the loop current verification circuitry includes a resistor coupled in series with the two wire process control loop. ### Claim 3 (depends on 1) The apparatus of claim 1 wherein the loop current verification circuitry includes a comparator configured to compare a signal level and provide an output related to electrical current in the two wire process control loop. ### Claim 4 (depends on 1) The apparatus of claim 1 wherein the loop current verification circuitry includes an analog to digital converter configured to measure a signal level related to current through the two wire process control loop. ### Claim 5 (depends on 1) The apparatus of claim 1 including: plus and minus terminals and a common return; a sense resistance conducting the loop current from the common return to the minus terminal; an amplifier having a signal return coupled to the minus terminal and an amplified output. ### Claim 6 (depends on 1) The apparatus of claim 1 wherein the loop current verification circuitry compares a measured loop current value with an expected loop current value and provides an output related to the comparison. ### Claim 7 (depends on 1) The apparatus of claim 1 including a local output responsive to the loop current verification circuitry. ### Claim 8 (depends on 1) The apparatus of claim 1 wherein the loop current verification circuitry compares measured value to a threshold. ### Claim 9 (depends on 1) The apparatus of claim 1 wherein the loop current verification circuitry is configured to actuate calibration of the loop current output circuitry. ### Claim 10 (depends on 1) The apparatus of claim 1 including an output configured to place an output from the loop current verification circuitry on the two wire process control loop indicative of a detected error. ### Claim 11 (depends on 1) The apparatus of claim 1 including a visual indication output. ### Claim 12 (depends on 1) The apparatus of claim 1 including a digital indication output. ### Claim 13 (depends on 1) The apparatus of claim 1 including a wireless indication output. ### Claim 14 (depends on 1) The apparatus of claim 1 wherein the loop current output is compensated in response to the detected error. ### Claim 15 (depends on 1) The apparatus of claim 1 wherein the loop current verification circuitry is configured to measure a value of an independent reference. ### Claim 16 A method in a process device for verifying loop current in a two wire process control loop, comprising: sensing a process variable; adjusting a loop current in the two wire process control loop as a function of the sense process variable; verifying a value of the current in two wire process control loop using at least one electrical component which is independent of electrical components used to set the loop current in the two wire process control loop. ### Claim 17 (depends on 16) The method of claim 16 wherein verifying the value of the current includes sensing a voltage drop across a resistance coupled in series with the two wire process control loop. ### Claim 18 (depends on 16) The method of claim 16 wherein verifying a value of the current includes comparing a signal level and providing an output related to electrical current in the two wire process control loop. ### Claim 19 (depends on 16) The method of claim 16 including digitizing a signal level related to current through the two wire process control loop. ### Claim 20 (depends on 16) The method of claim 16 wherein verifying the loop current includes comparing a sensed loop current value with an expected loop current value and providing an output related to the comparison. ### Claim 21 (depends on 16) The method of claim 16 wherein the step of verifying is at least partially implemented in a microprocessor. ### Claim 22 (depends on 16) The method of claim 16 including: sensing the loop current from a common return to a minus terminal; and providing a signal return coupled to the minus terminal and an amplified output.