Resistance thermometer characteristics and response time testing

Based on a lumped-parameter representation of transient heat transfer in cylindrical geometry, a method was developed which enables the time constant of a platinum resistance temperature detector (PRTD) to be calculated in situ. Application of this method (called the loop current step response (LCSR) method) yielded errors in the time constant calculation of over 20 percent. Further analytical and numerical studies were made resulting in a correlation which can be used with the LCSR method which reduced the error to O-10 percent. The correlation is based on the fact that the ratio of the first two poles (used in the LCSR analysis) were adequate to predict the contribution of higher order poles required in an exact solution.

A sensitivity analysis of a PRTDs time constant to changes in material properties was performed for two sensors typical of the type used in Westinghouse and Combustion Engineering pressurized water reactors.

A mode of possible sensor degradation, i.e., changes in the ceramic cement used in the construction process, was studied with the result being that the cement was a probable candidate for causing the response time of a PRTD to change.