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Detecting thermocouple failure using loop resistance

  • US 6,983,223 B2
  • Filed: 04/29/2003
  • Issued: 01/03/2006
  • Est. Priority Date: 04/29/2003
  • Status: Active Grant
First Claim
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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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