US 6,983,223 B2 | ||
Detecting thermocouple failure using loop resistance | ||
William C. Schuh, Delavan, Wis. (US) | ||
Assigned to Watlow Electric Manufacturing Company, St. Louis, Mo. (US) | ||
Filed on Apr. 29, 2003, as Appl. No. 10/425,391. | ||
Prior Publication US 2004/0220775 A1, Nov. 04, 2004 | ||
Int. Cl. G06F 11/30 (2006.01) |
U.S. Cl. 702—185 | 33 Claims |
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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