System and method for detecting fluid in terminal block area of field device
First Claim
1. A method of detecting fluid in a terminal block of a field device, the method comprising:
- measuring an initial impedance of a current loop connecting the field device to a control room when no fluid is present in the terminal block of the field device, wherein the current loop is connected to the field device by first and second terminals located in the terminal block of the field device;
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;
applying an alternating current (AC) test signal at a selected frequency to the current loop;
measuring a resulting AC voltage magnitude in response to the AC test signal; and
detecting a change in impedance of the current loop by 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, wherein a detected change in the impedance of the current loop indicates the presence of fluid in the terminal block between the first and second terminals.
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Accused Products
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.
14 Citations
21 Claims
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1. A method of detecting fluid in a terminal block of a field device, the method comprising:
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measuring an initial impedance of a current loop connecting the field device to a control room when no fluid is present in the terminal block of the field device, wherein the current loop is connected to the field device by first and second terminals located in the terminal block of the field device; 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; applying an alternating current (AC) test signal at a selected frequency to the current loop; measuring a resulting AC voltage magnitude in response to the AC test signal; and detecting a change in impedance of the current loop by 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, wherein a detected change in the impedance of the current loop indicates the presence of fluid in the terminal block between the first and second terminals. - View Dependent Claims (2, 3, 4)
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5. A method of detecting fluid in a terminal block of a field device, the method comprising:
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applying an initial AC test signal at a selected frequency to a current loop that connects the field device to a control room, wherein the two-wire current loop is connected to the field device by first and second terminals located in the terminal block of the field device -and the initial AC test signal is provided when no fluid is present within the terminal block; measuring an initial AC voltage magnitude in response to the initial AC test signal; applying a subsequent AC test signal at the selected frequency to the current loop; measuring a subsequent AC voltage magnitude generated in response to the subsequent AC test signal; and detecting a change in impedance of the current loop by comparing the initial AC voltage magnitude with the subsequent AC voltage magnitude, wherein a detected change in the impedance of the current loop indicates the presence of fluid in the terminal block between the first and second terminals. - View Dependent Claims (6, 7, 8, 9)
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10. A field device which detects fluid within a terminal block area of the field device, the field device comprising:
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a terminal block area; a first terminal and a second terminal enclosed within the terminal block area of the field device, wherein the field device receives power and communicates with a control room by way of a two-wire pair that is connected to the first terminal and the second terminal, respectively, to form a current loop, wherein an accumulation of fluid within the terminal block causes fluid to come into contact with the first terminal and the second terminal; a sensor device for sensing a process variable; a current regulation circuit connected between the first terminal and the second terminal for communicating the sensed process variable over the current loop to the control and for generating on the current loop 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, characterized by a change in impedance of the current loop caused by the presence of fluid between the first terminal and the second terminal, is detected based on the measured AC voltage magnitude. - View Dependent Claims (11, 12, 13, 14)
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15. A system for detecting the presence of fluid in a terminal block area of a field device, the system comprising:
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a terminal block area; a first terminal and a second terminal enclosed within the terminal block area of the field device, wherein the field device receives power and communicates with a control room by way of a two-wire pair that is connected to the first terminal and the second terminal, respectively, to form a current loop, wherein the accumulation of fluid within the terminal block causes fluid to come into contact with the first terminal and the second terminal; means for applying an alternating current (AC) test signal at a selected frequency to the current loop; 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, characterized by a change in impedance of the current loop caused by the presence of fluid between the first terminal and the second terminal, that is detected based on the measured AC voltage magnitude. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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Specification