Detecting thermocouple failure using loop resistance
First Claim
1. A method of detecting thermocouple failure in a temperature monitoring circuit, the method comprising:
- inputting and storing manufacturers values for an initial resistance Rmo and a temperature coefficient of resistance α
for a thermocouple based on the thermocouple part number;
measuring a loop resistance LR at an indicated initial temperature Tmo;
computing and storing an initial circuit resistance Rc of the unsheathed portion of the temperature monitoring circuit, based on the LR measurement and initial temperature Tmo;
measuring a current loop resistance LR at a current indicated temperature Tm;
computing a thermocouple confidence level % CL based on comparing a predicted LR, to the current measured LR at the current indicated temperature Tm according to a thermocouple failure detection algorithm;
determining whether the thermocouple confidence level % CL has exceeded a predetermined limit;
measuring another current loop resistance LR at the current indicated temperature Tm, if the % CL has not exceeded the predetermined limit;
generating an alarm for maintenance of the thermocouple, if the % CL has exceeded the predetermined limit; and
wherein the limit of the thermocouple confidence level corresponds to an impending thermocouple failure and the prediction thereof.
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Accused Products
Abstract
A system and method is presented for detecting the degradation of a thermocouple circuit prior to failure and the prediction of certain impending thermocouple failures. The detection system monitors the loop resistance of the measurement circuit and isolates the heat affected loop resistance changes from the degraded circuit changes. The monitoring circuit is divided into a sheathed portion, generally exposed to the temperature measurement, and an unsheathed portion of the monitoring system generally at ambient temperature. An algorithm is provided for standard instrumentation systems to predict certain types of impending failure in thermocouple temperature measurement circuits. The algorithm essentially compensates the loop resistance measurements by removing the heat affected sheathed portion loop resistance changes computed from the initial unsheathed portion resistance based on manufacturers parameters specific to a thermocouple and an initial loop resistance measurement, leaving only those changes due to degradations in the unsheathed portion of the circuit.
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Citations
33 Claims
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1. A method of detecting thermocouple failure in a temperature monitoring circuit, the method comprising:
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inputting and storing manufacturers values for an initial resistance Rmo and a temperature coefficient of resistance α
for a thermocouple based on the thermocouple part number;measuring a loop resistance LR at an indicated initial temperature Tmo; computing and storing an initial circuit resistance Rc of the unsheathed portion of the temperature monitoring circuit, based on the LR measurement and initial temperature Tmo; measuring a current loop resistance LR at a current indicated temperature Tm; computing a thermocouple confidence level % CL based on comparing a predicted LR, to the current measured LR at the current indicated temperature Tm according to a thermocouple failure detection algorithm; determining whether the thermocouple confidence level % CL has exceeded a predetermined limit; measuring another current loop resistance LR at the current indicated temperature Tm, if the % CL has not exceeded the predetermined limit; generating an alarm for maintenance of the thermocouple, if the % CL has exceeded the predetermined limit; and wherein the limit of the thermocouple confidence level corresponds to an impending thermocouple failure and the prediction thereof. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of detecting thermocouple failure in a temperature monitoring circuit, the method comprising:
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inputting and storing manufacturers values for an initial resistance Rm0 and a temperature coefficient of resistance α
for a thermocouple based on the thermocouple part number;measuring a loop resistance LR at an indicated initial temperature Tmo; computing and storing an initial circuit resistance Rc of the unsheathed portion of the temperature monitoring circuit, based on the LR measurement and initial temperature Tm0; measuring a current loop resistance LR at a current indicated temperature Tm; computing a thermocouple figure of merit Z based on comparing a predicted LR, to the current measured LR at the current indicated temperature Tm according to a thermocouple failure detection algorithm; determining whether the thermocouple figure of merit Z has exceeded a predetermined limit; measuring another current loop resistance LR at the current indicated temperature Tm, if the Z has not exceeded the predetermined limit; generating an alarm for maintenance of the thermocouple, if the Z has exceeded the predetermined limit; and wherein the limit of the thermocouple figure of merit Z corresponds to an impending thermocouple failure and the prediction thereof. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A system for detecting thermocouple failure, comprising:
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a temperature measuring component having one or more thermocouples coupled thereto wherein the coupling to each thermocouple is by no more than the two thermocouple leads; a memory storage component; an analyzer operably coupled to the temperature measuring component and the storage component, the analyzer having a prediction algorithm used by the analyzer to detect thermocouple degradations and to make thermocouple failure predictions; wherein temperature signals generated by respective thermocouples are provided to the analyzer over the no more than two thermocouple leads and utilized within the prediction algorithm within the analyzer to generate the thermocouple degradation detection, the level of which provides one of an indication of thermocouple health and an indication of imminent thermocouple failure; and wherein the prediction algorithm is performed by the analyzer and conveyed by a computer readable medium. - View Dependent Claims (22, 23, 24, 25, 26, 27)
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28. A system for detecting thermocouple failure, comprising:
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one or more thermocouples to monitor temperature within the system; and a computer coupled to the one or more thermocouples, said coupling to each thermocouple being by no more than the two leads of the thermocouple; wherein temperature signals generated by respective thermocouples are provided to the computer over the no more than two thermocouple leads and utilized within a prediction algorithm that is embedded within the computer to generate a thermocouple confidence level % CL, which level provides one of an indication of thermocouple health and an indication of imminent thermocouple failure; wherein the prediction algorithm is performed by the computer and conveyed by a computer readable medium. - View Dependent Claims (29, 30, 31, 32)
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33. A system for detecting thermocouple failure, comprising:
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one or more thermocouples to monitor temperature within the system; an input for receiving manufacturers values for an initial resistance Rm0 and a temperature coefficient of resistance α
for each thermocouple based on the thermocouple part number for each;a memory for storing the received manufacturers values for the initial resistance Rm0 and the temperature coefficient of resistance α
; anda computer coupled to the one or more thermocouples, said coupling to each thermocouple being by no more than the two leads of the thermocouple, said computer configured to compute and store in the memory an initial loop resistance of the thermocouple; wherein temperature signals generated by respective thermocouples and provided by the no more than two thermocouple leads are provided to the computer and utilized to measure an initial loop resistance at an indicated initial temperature and a current loop resistance at a current indicated temperature, and a prediction algorithm that is embedded within the computer to generate a thermocouple figure of merit Z based on comparing a predicted loop resistance to the current measured loop resistance according to a thermocouple failure detection algorithm; wherein the prediction algorithm is performed by the computer and conveyed by a computer readable medium, wherein the computer is configured to compare the thermocouple figure of merit Z to a predetermined limit and generate an alarm for maintenance when the determined thermocouple figure of merit Z exceeds the predetermined limit, and wherein the limit of the thermocouple figure of merit Z corresponds to an impending thermocouple failure and the prediction thereof.
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Specification