System and method for detecting fluid in terminal block area of field device

• US 20080156090A1
• Filed: 12/28/2006
• Published: 07/03/2008
• Est. Priority Date: 12/28/2006
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Wehrs, David L.
• Granted Patent: US 7,521,944 B2
• Time in Patent Office: Days
• US Class Current: 73/290R
• CPC Class Codes: G01M 3/16 using electric detection means G01M3/045, G01M3/06, G01M3/12, G01M3/20, G01M3/24, G01M3/26 take precedence
• CPC Class Codes: G01M 3/40 by using electric means, e.g. by observing electric discharges
• CPC Class Codes: H05K 7/1462 for programmable logic controllers [PLC] for automation or industrial process control

Abstract

A field device detects the presence of fluid in the terminal block area of the field device by generating an alternating current (AC) test current signal and measuring the amplitude of the resulting AC voltage signal. The field device includes a first terminal and a second terminal adapted for connection to a control room through a twisted-wire pair current loop. Impedance of the current loop is increased by the presence of fluid between the first terminal and the second terminal. By providing an AC test current signal to the control loop and measuring a resulting AC voltage magnitude, the impedance of the control loop can be determined. Increased impedance in the control loop indicates the presence of water in the terminal block.

Claims

1. A method of detecting fluid in a terminal block of a field device, the method comprising:

applying an alternating current (AC) test signal between a first terminal and a second terminal within the terminal block of the field device;

measuring a resulting AC voltage magnitude in response to the AC test signal; and

detecting the presence of fluid in the terminal block based on the measured AC voltage magnitude.

2. The method of claim 1, wherein applying the AC test signal between the first and second terminals includes:

modulating the current provided between the first and second terminals at a selected frequency using digital communication capabilities of the field device.

3. The method of claim 1, further including:

measuring an initial impedance associated with a current loop connecting the field device to a control room when no fluid is present in the terminal block of the field device; and

selecting a threshold AC voltage magnitude value based on the measured initial impedance of the current loop in which no fluid is present in the terminal block.

4. The method of claim 3, wherein detecting the presence of fluid in the terminal block includes:

comparing the AC voltage magnitude measured in response to the AC test signal to the threshold AC voltage magnitude selected based on the initial impedance of the current loop.

5. The method of claim 1, including:

applying an initial AC test signal between a first terminal and a second terminal when no fluid is present within the terminal block; and

measuring an initial AC voltage magnitude in response to the initial AC test signal.

6. The method of claim 5, wherein detecting the presence of fluid in the terminal block includes:

comparing the measured AC voltage magnitude to the initial AC voltage magnitude.

7. The method of claim 5, wherein a first frequency associated with the initial AC signal is approximately equal to a second frequency associated with the AC test signal.

8. The method of claim 5, further including:

storing the initial AC voltage magnitude measured in response to the initial AC test signal to memory located within the field device;

storing the AC voltage magnitude measured in response to the AC test signal to the memory located within the field device, wherein the initial AC voltage magnitude and the AC voltage magnitude measured in response to the AC test signal are made available to a microprocessor for determining whether fluid is present in the terminal block.

9. The method of claim 5, further including:

communicating the initial AC voltage magnitude measured in response to the initial AC test signal to the control room;

communicating the AC voltage magnitude measured in response to the AC test signal to the control room, wherein the control room determines whether fluid is present in the terminal block based on the initial AC voltage magnitude and the AC voltage magnitude.

10. The method of claim 1, further including:

notifying a control room connected to the field device of the presence of fluid in the terminal block area of the field device.

11. The method of claim 1, wherein measuring the resulting AC voltage amplitude includes:

using a hand-held device connected to the first and second terminals of the field device.

12. A field device which detects fluid within a terminal block area of the field device, the field device comprising:

a first terminal and a second terminal connected to communicate with a control room;

a current regulation circuit connected between the first and second terminal for generating an alternating current (AC) test signal at a selected frequency; and

an AC measurement device connected to measure a resulting AC voltage magnitude generated in response to the AC test signal provided by the current regulation circuit, wherein the presence of fluid within the terminal block area is detected based on the measured AC voltage magnitude.

13. The field device of claim 12, wherein the AC measurement device includes:

a resistive element; and

an AC coupled receiving device connected across the resistive element to measure the resulting AC voltage magnitude.

14. The field device of claim 12, further including:

a microprocessor connected to receive input from the AC measurement device regarding the measured AC voltage magnitude, wherein the microprocessor determines whether fluid is present in the terminal block based on the measured AC voltage magnitude.

15. The field device of claim 14, wherein the microprocessor determines whether fluid is present in the terminal block by comparing an initial AC voltage magnitude measured in response to an initial AC test signal to a subsequent AC voltage magnitude measured in response to a subsequent AC test signal.

16. The field device of claim 14, wherein the microprocessor determines whether fluid is present in the terminal block by comparing the resulting AC voltage magnitude measured in response to the AC test signal to a threshold AC voltage magnitude selected based on an initial impedance associated with the current loop upon initialization of the system.

17. A system for detecting the presence of fluid in a terminal block area of a field device, the system comprising:

means for applying an alternating current (AC) test signal between a first terminal and a second terminal within the terminal block of the field device;

means for measuring a resulting AC voltage magnitude in response to the AC test signal; and

means for detecting the presence of fluid in the terminal block based on the measured AC voltage magnitude.

18. The system of claim 17, wherein the means for applying the AC test signal between the first and second terminals includes:

a current regulation circuit located within the field device that modulates the current provided between the first and second terminals at a selected frequency using digital communication capabilities of the field device.

19. The system of claim 17, wherein the means for applying an AC test signal and the means for measuring a resulting AC voltage magnitude are located on a communication chipset within the field device.

20. The system of claim 17, wherein the means for measuring a resulting AC voltage magnitude includes:

a measurement resistor connected to receive the AC test signal generated by the means for applying an AC test signal; and

an AC coupled measurement device for measuring the AC voltage magnitude generated across the measurement resistor.

21. The system of claim 17, wherein the means for detecting the presence of fluid in the terminal block compares the AC voltage magnitude measured in response to the AC test signal to a threshold AC voltage magnitude selected based on the initial impedance of the current loop to detect the presence of fluid in the terminal block.

22. The system of claim 17, wherein the means for detecting the presence of fluid in the terminal block compares the AC voltage magnitude measured in response to the AC test signal to an initial AC voltage magnitude measured in response to an initial AC test signal to detect the presence of fluid in the terminal block.

23. The system of claim 22, further including:

means for storing the initial AC voltage magnitude measured in response to the initial AC test signal to memory located within the field device; and

means for storing the AC voltage magnitude measured in response to the AC test signal to the memory located within the field device.