The Loop Current Step Response (LCSR) method is used for in–situ response time testing of temperature sensors as installed in an industrial process. This paper presents the theoretical foundation of the LCSR (test theory, LCSR equation and test procedures) and the author's research to validate its use in nuclear power industry applications. The validity of the LCSR method depends on how well the temperature sensor design satisfies LCSR test assumptions, the quality of LCSR data in terms of signal–to–noise ratio, the application of proper sampling parameters for the LCSR data acquisition phase, and the suitability of the algorithms and fitting processes used in the LCSR data analysis stage. In multiple tests the author demonstrated a ±10% agreement between the median values of the response time produced by the plunge and LCSR methods. The plunge test is the standard method for laboratory measurement of the response time of temperature sensors.
Keywords: process instrumentation, dynamic measurements, response time testing, in–situ testing, response time degradation, resistance temperature detectors, loop current step response test, nuclear power plants, NPP: nuclear energy, temperature sensors, sensor design, signal–to–noise ratio, sampling parameters, data acquisition, plunge test