Device and method for monitoring the condition of a thermocouple

Abstract

A device and method for monitoring the condition of a thermocouple. In a preferred embodiment the device comprises a pair of thermocouples, each thermocouple comprising first and second thermoelement wires, and a diagnostic element selectively electrically coupled at a junction with one of the thermoelements. In a preferred embodiment, the diagnostic element is selected such that it is more stable at the expected operating temperature range of the thermocouple than the thermoelement wires themselves are. The diagnostic element can be switched into electrical connection with any of the thermoelements forming the thermocouples to thereby define one or more loops. An initial loop resistance is measured and recorded around each of the thermoelement/diagnostic element loops. This initial resistance is stored in a calibration matrix as a reference value. The initial loop resistance may be taken as part of a calibration process or during initial operation of the thermocouple. Subsequent loop resistance measurements are then taken over time as the thermocouples age and compared against the reference value. By comparing the reference value to subsequent measurements, the level of degradation of the thermoelements can be monitored. Further, in an embodiment utilizing an electrically conductive sheath material, a conductive sheath wire may be used to connect the sheath to any one of the thermoelements or the diagnostic element. By monitoring the resistance in a measurement circuit formed thereby, potential or actual virtual junction error in the thermocouple assembly may be detected.

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