# US 8,786,128 B2 · Two-wire industrial process field device with power scavenging > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,786,128 B2 - Document ID: US8786128B2 - Status: Granted - Kind: B2 - Application number: 13/098,678 - Filed: 2011-05-02 - Published: 2011-11-17 - Granted: 2014-07-22 - Earliest claimed: 2010-05-11 - Assignees: Rosemount Inc. - Applicants: John P. Schulte - Inventors: John P. Schulte - Web page: https://patentgrep.com/patent/US8786128B2 ## CPC - G05B 19/0423: {Input/output} - 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 process field device for use in monitoring or controlling an industrial process includes first and second loop terminals configured to couple to a two-wire industrial process control loop. Field device circuitry is configured to monitor or control a process variable of the industrial process. The field device circuitry is powered by power connections from the two-wire industrial process control loop. A current regulator is connected in series with the two-wire industrial process control loop, the first and second loop terminals and the field device circuitry. The current regulator is configured to control a loop current flowing through the two-wire process control loop. A voltage regulator is connected in parallel with the current regulator and in series with the two-wire industrial process control loop, first and second loop terminals and field device circuitry. The voltage regulator is configured to control a voltage across the field device circuitry. ## Claims ### Claim 1 A process field device for use in monitoring or controlling an industrial process, comprising: first and second loop terminals configured to couple to a two-wire industrial process control loop; field device circuitry configured to monitor or control a process variable of the industrial process, the field device circuitry powered by power from the two-wire industrial process control loop; a current regulator connected in series with the two-wire industrial process control loop, the first and second loop terminals and the field device circuitry, the current regulator configured to control a loop current flowing through the two-wire process control loop; and a voltage regulator connected in parallel with the current regulator and in series with the two-wire industrial process control loop, the first and second loop terminals and field device circuitry, the voltage regulator configured to control a voltage across the field device circuitry. ### Claim 2 (depends on 1) The process field device of claim 1 including a bulk capacitance connected in parallel with the field device circuitry configured to store electrical energy. ### Claim 3 (depends on 1) The process field device of claim 1 including a shunt current regulator configured to control the loop current flowing through the process control loop in response to a measured process variable. ### Claim 4 (depends on 1) The process field device of claim 1 wherein the current regulator is configured to modulate a digital signal onto the loop current flowing through the two-wire industrial process control loop. ### Claim 5 (depends on 4) The process field device of claim 4 wherein the field device circuitry includes a modem coupled to the current regulator configured to modulate the digital signal. ### Claim 6 (depends on 1) The process field device of claim 1 wherein the two wire process control loop operates in accordance with the HART® communication protocol in which digital information is modulated onto an analog current level signal. ### Claim 7 (depends on 1) The process field device of claim 1 wherein the loop current varies between 4 mA and 20 mA and is representative of a measured process variable. ### Claim 8 (depends on 1) The process field device of claim 1 wherein the voltage regulator includes a field effect transistor coupled in series with the two wire process control loop and an operational amplifier having a voltage reference input. ### Claim 9 (depends on 8) The process field device of claim 8 wherein the voltage regulator receives a negative feedback related to a voltage at the output of the field effect transistor. ### Claim 10 (depends on 1) The process field device of claim 1 wherein the current regulator comprises a field effect transistor coupled in series with the two wire process control loop and an operational amplifier configured to receive a modulated digital signal. ### Claim 11 (depends on 10) The process field device of claim 10 wherein the current regulator receives negative feedback related to the current flowing through the field effect transistor. ### Claim 12 A method of providing power to a process field device for use in monitoring or controlling an industrial process, comprising: coupling first and second loop terminals to a two wire industrial process control loop; powering field device circuitry with power received from the two wire process control loop and monitoring or controlling a process variable of the industrial process with the field device circuitry; regulating a loop current flow through the two wire process control loop using a current regulator which is coupled in series with the first and second loop terminals and the field device circuitry; and regulating a voltage across the field device circuitry using a voltage regulator connected in parallel with the current regulator and in series with the two wire process control loop, the first and second loop terminals and the field device circuitry. ### Claim 13 (depends on 12) The process field device of claim 12 including providing a bulk capacitance connected in parallel with the field device circuitry configured to store electrical energy. ### Claim 14 (depends on 12) The process field device of claim 12 including controlling the loop current flowing through the process control loop with a shunt current regulator in response to a measured process variable. ### Claim 15 (depends on 12) The method of claim 12 including modulating a digital signal onto the loop current flowing through the two-wire industrial process control loop. ### Claim 16 (depends on 12) The method of claim 12 wherein the voltage regulator includes a field effect transistor coupled in series with the two wire process control loop and an operational amplifier having a voltage reference input. ### Claim 17 (depends on 16) The method of claim 16 wherein the voltage regulator receives a negative feedback related to the current flowing through the field effect transistor. ### Claim 18 (depends on 12) The method of claim 12 wherein the current regulator comprises a field effect transistor coupled in series with the two wire process control loop and an operational amplifier configured to modulate a digital signal on to the two wire process control loop.