VARIABLE LIFTOFF VOLTAGE PROCESS FIELD DEVICE

• US 20090224730A1
• Filed: 03/10/2008
• Published: 09/10/2009
• Est. Priority Date: 03/10/2008
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Schulte, John P.
• Granted Patent: US 7,970,063 B2
• Time in Patent Office: Days
• US Class Current: 323/220
• CPC Class Codes: G05B 19/0423 Input/output
• CPC Class Codes: G05B 2219/25428 Field device
• CPC Class Codes: G08C 19/02 in which the signal transmitted is magnitude of current or voltage G08C19/36, G08C19/38 take precedence
• CPC Class Codes: G08C 2201/10 Power supply of remote control devices

Abstract

A field transmitter includes field device circuitry configured to measure or control a process variable. A first process control loop terminal is configured to couple to a two-wire process control loop which carries a loop current. A second process control loop terminal configured to couple to the two-wire process control loop. A switching regulator has an input and an output. The output is coupled to the transmitter circuitry and arranged to provide power to the transmitter circuitry. A variable voltage source having an input electrically coupled to the first process control loop terminal, and a voltage output coupled to the input of the switching regulator and a control input. The voltage output is a function of the control input.

Claims

1. A field device, comprising:

field device circuitry configured to measure or control a process variable;

a first process control loop terminal configured to couple to a two-wire process control loop, the two-wire process control loop carrying a loop current;

a second process control loop terminal configured to couple to the two-wire process control loop;

a switching regulator having an input and an output, the output coupled to the field device circuitry and arranged to provide power to the field device circuitry; and

a variable voltage source having an input electrically coupled to the first process control loop terminal, and a voltage output coupled to the input of the switching regulator and a control input, wherein the voltage output is a function of the control input.

2. The apparatus of claim 1 wherein the voltage output from the variable voltage source has a non-linear relationship to loop current.

3. The apparatus of claim 1 wherein the voltage output from the variable voltage source has a linear relationship to loop current.

4. The apparatus of claim 1 including a shunt regulator configured to shunt current to the two-wire process control loop.

5. The apparatus of claim 1 wherein the variable voltage source comprises a voltage regulator.

6. The apparatus of claim 1 wherein the variable voltage source input is coupled to the field device circuitry.

7. The apparatus of claim 6 including a shunt current regulator configured to shunt current in excess of a quiescent current required by the field device, and wherein the shunt current regulator is responsive to the field device circuitry.

8. The apparatus of claim 1 wherein the field device comprises a transmitter.

9. The apparatus of claim 8 wherein the loop current is related to a process variable.

10. A method of powering a process field device, comprising:

coupling first and second process control loop terminals of the field device to a two-wire process control loop, the two-wire process control loop carrying a loop current;

receiving an input voltage at a switching regulator;

providing power to field device circuitry from an output of the switching regulator from the input voltage; and

controlling the input voltage to the switching regulator.

11. The method of claim 10 wherein the voltage input to the switching regulator has a non-liner relationship to loop current.

12. The method of claim 10 wherein the voltage input to the switching regulator has a linear relationship to loop current.

13. The method of claim 10 including to shunting current to the two-wire process control loop.

14. The method of claim 10 wherein controlling the input voltage to the switching regulator comprises controlling a voltage regulator.

15. The method of claim 10 including controlling the loop current based upon a process variable.