Process control loop signal converter

• US 7,016,741 B2
• Filed: 10/14/2003
• Issued: 03/21/2006
• Est. Priority Date: 10/14/2003
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Arntson, Douglas W.
• Primary Examiner(s): Picard, Leo
• Assistant Examiner(s): KOSOWSKI, ALEXANDER J
• Application Number:
  US10/685,167
• Publication Number:
  US 20050080493A1
• Time in Patent Office: 889 Days
• Field of Search: 700/1, 700/9, 700/11, 700/12, 700/19, 700/37, 700/282, 700/39, 700/90, 700/2, 370/410, 340/825, 340/825.01
• US Class Current: 700/19
• CPC Class Codes: G01D 21/00 Measuring or testing not otherwise provided for
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G05B 19/0423 Input/output
• CPC Class Codes: G05B 2219/25006 Interface connected to fieldbus
• CPC Class Codes: G05B 2219/25428 Field device

Abstract

A device for use in a process control system includes a first pair of electrical connections configured to couple to a two-wire process control loop. The loop includes a two-wire process variable transmitter. A second pair of electrical connections is configured to couple to an input channel of a process device having multiple input channels. An electrical component is connected in series in the loop for use in digital communication with the two-wire process variable transmitter.

Claims

1. A signal conversion device for use in a process control system, comprising:

a first pair of electrical connections configured to couple to a two-wire process control current loop which includes a two-wire process variable transmitter which provides an analog current level on the two-wire process control current loop related to a sensed process variable;

a second pair of electrical connections configured to couple to an analog voltage input channel of a process device; and

a first electrical component electrically connected to a first electrical connection of the first pair of electrical connections and a first electrical connection of the second pair of electrical connections, the first electrical component further configured to couple to a digital communicator to provide a connection for digital communication between the digital communicator and the two-wire process variable transmitter;

a second electrical component connected between the first and a second electrical connection of the second pair of electrical connections to provide a connection for communication with the voltage input channel of the process device with an analog voltage related to the analog current level on the two-wire process control loop; and

a switch connected in parallel with the first electrical component between the first electrical connector of the first pair of electrical connections and the first electrical connector of the second pair of electrical connectors, the switch configured to selectively allow digital communication by the digital communicator through the first electrical component with the two-wire process variable transmitter.

2. The apparatus of claim 1 wherein the first electrical component is in series between the first electrical connection of the first pair of electrical connections and a first electrical connection.

3. The apparatus of claim 1 wherein the first electrical component comprises a resistor.

4. The apparatus of claim 3 wherein the resistor has a resistance of between about 230 and about 600 ohms.

5. The apparatus of claim 1 wherein the second electrical component is in series between the first and the second electrical connections of the second pair of electrical connections.

6. The apparatus of claim 1 wherein the second electrical component comprises a resistor.

7. The apparatus of claim 6 wherein the second electrical component comprises a resistor.

8. The apparatus of claim 6 wherein the resistance of the resistor has a resistance of 5 ohms.

9. The apparatus of claim 1 wherein a current through the two-wire process control current loop ranges between about 4 mA and 20 mA.

10. The apparatus of claim 1 wherein a voltage between the second pair of electrical connections ranges between about 20 mVolts and about 100 mVolts.

11. The apparatus of claim 1 including a power supply.

12. The apparatus of claim 11 wherein the power supply provide a DC output of between about 10 V and about 50 V and is coupled in series with the two-wire process control current loop.

13. The apparatus of claim 1 including a output indicative of an active power supply on the two-wire process control current loop.

14. The apparatus of claim 13 wherein the output comprises an optical output.

15. The apparatus of claim 1 wherein the process device includes multiple input channels.

16. The apparatus of claim 1 wherein the first pair of electrical connections is configured for HART®

communication.

17. A signal conversion device for use in a process control system, comprising:

a first pair of electrical connections configured to couple to a two-wire process control current loop which includes a two-wire process variable transmitter which provides an analog current level on the two-wire process control current loop related to a sensed process variable;

a second pair of electrical connections configured to couple to an analog voltage input channel of a process device; and

digital communication coupling means electrically coupled between a first electrical connector of the first pair of electrical connections and a first electrical connector of the second pair of electrical connectors for coupling a digital communication signal between a digital communicator and the two-wire process variable transmitter through the first pair of electrical connections;

switch means connected in parallel with the digital communication coupling means between the first electrical connector of the first pair of electrical connections and the first electrical connector of the second pair of electrical connectors for selectively bypassing the digital communication coupling means; and

electrical component means connected between the first and a second electrical connectors of the second pair of electrical connectors for communicating with the voltage input channel of the process device an analog voltage related to the analog current level on the two-wire process control loop.

18. The apparatus of claim 17 wherein the digital communication coupling means comprises a resistor.

19. The apparatus of claim 17 wherein the electrical component means comprises a resistor.

20. A method for use in a process control system, comprising:

providing a process control current loop for coupling to a two-wire process variable transmitter which provides an analog current level on the two-wire process control current loop related to a sensed process variable;

providing a first pair of electrical connections on the two-wire process control current loop for coupling to a digital communicator;

providing a second pair of electrical connections for coupling to an analog voltage input channel of a process device;

providing a first electrical component between a first electrical connector of the first pair of electrical connectors and a first electrical connector of the second pair of electrical connections configured to couple to the digital communicator for digital communication between the digital communicator and the two-wire process variable transmitter;

providing a second electrical component between the first and a second electrical connection of the second pair of electrical connections for communication with the voltage input channel of the process device using an analog voltage related to the analog current level on the tow-wire process control loop;

providing a switch in parallel with the first electrical component between the first electrical connector of the first pair of electrical connectors and the first electrical connections of the second pair of electrical connections;

opening the switch and digitally communicating with the transmitter through the first electrical component; and

closing the switch and bypassing the first electrical component.

21. The method of claim 20 wherein the first electrical component comprises a resistor.

22. The method of claim 20 wherein the second electrical component comprises a resistor.

23. The method of claim 20 wherein the voltage drop across the second pair of electrical connections is between about 20 mVolts and about 100 mVolts.

24. The method of claim 20 wherein a two-wire process control current loop carries an electrical current between about 4 mA and 20 mA.

25. The method of claim 20 including digitally communicating with the two-wire process variable transmitter.

26. The method of claim 25 wherein digital communicating comprises communicating in accordance with the HART®

standard.