Method for in-situ restoration of plantinum resistance thermometer calibration
First Claim
1. A method for the in situ restoration of a platinum resistance thermometer, which has become decalibrated due to oxide surface film formation and/or strain-related damage, to a stress-free calibration condition wherein said thermometer includes a platinum resistor sensing element whose resistance varies with the temperature of said element in accordance with a known relationship comprising the step of:
- passing a controlled dc current through said platinum resistor sensing element, said current having a magnitude sufficient to raise the temperature of said element to its oxide decomposition and annealing temperature and said current being maintained for a heating period sufficient to restore said element to an oxide free surface and stress-free calibration condition.
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Abstract
A method is provided for in-situ restoration of platinum resistance thermometers (PRT'"'"'s) that have undergone surface oxide contamination and/or strain-related damage causing decalibration. The method, which may be automated using a programmed computer control arrangement, consists of applying a dc heating current to the resistive sensing element of the PRT of sufficient magnitude to heat the element to an annealing temperature and maintaining the temperature for a specified period to restore the element to a stress-free calibration condition. The process anneals the sensing element of the PRT without subjecting the entire PRT assembly to the annealing temperature and may be used in the periodic maintenance of installed PRT'"'"'s.
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Citations
4 Claims
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1. A method for the in situ restoration of a platinum resistance thermometer, which has become decalibrated due to oxide surface film formation and/or strain-related damage, to a stress-free calibration condition wherein said thermometer includes a platinum resistor sensing element whose resistance varies with the temperature of said element in accordance with a known relationship comprising the step of:
passing a controlled dc current through said platinum resistor sensing element, said current having a magnitude sufficient to raise the temperature of said element to its oxide decomposition and annealing temperature and said current being maintained for a heating period sufficient to restore said element to an oxide free surface and stress-free calibration condition. - View Dependent Claims (2, 3, 4)
Specification