In-situ response time estimation for thermocouples: Experimental Studies and Computational Modeling

Reactor protection systems are responsible for ensuring the safety of a nuclear reactor by limiting the consequences of a Postulated Initiating Event (PIE). Periodical surveillance of response time of a sensor is essential to comply with the stringent timing requirements for the actuation of protection systems. Thermocouples are one of the widely used temperature measuring sensors in industries since their discovery owing to their simplicity, robustness and wide measurement range. Thermocouple’s response time is conventionally measured using plunge test in a laboratory environment as per ASTM E-839 standard. However, response time of thermocouple may widely vary due to the installation conditions, heat transfer properties of the medium, process operating conditions, aging and repeated thermal cycling. Therefore, periodic surveillance of the response time of thermocouples becomes very important to comply with the safety and regulatory requirements. In this paper, a Loop Current Step Response Test based methodology for in-situ response time estimation of thermocouples is presented. Additionally, a COMSOL-based computational model for the problem is provided.