Experimental and analytical evaluation of the response time of high temperature fiber optic sensors

• A new method is developed to estimate response times of FO temperature sensors.
• Factors that influence the response time are discussed.
• Fiber optic sensors can have significantly smaller response time than thermocouples.

Gas temperature is a key variable in many high temperature applications. Sensors for measuring gas temperatures must be selected according to many different criteria, response time being one of the most important. Response time quantifies the time that the sensor needs to react to a sudden temperature variation. When rapid temperature fluctuations are expected, as in the case of fire tests, significant instantaneous errors can occur if the sensor response time is longer than the duration of the temperature fluctuation. Despite the importance of response time, there is no general agreement on how to quantify this value in high temperature fiber optic sensors.This paper proposes a methodology to estimate the response time of fiber optic temperature sensors based on an analytical model of the heat transfer between the sensor and its surroundings. The method is validated by an experimental study. In addition, the response times of three different high temperature fiber optic sensors developed by the authors are compared with each other and with the response time of some widely used thermocouples. The results show (i) that fiber optic sensors have a significantly shorter response time than thermocouples with similar packaging, (ii) that the response time is shorter during the heating phase than the cooling phase, and (iii) highlight the importance of considering this parameter in the sensor selection process.