Application Research Of Optical Fiber Temperature Sensors At Cryogenic Temperature

A real-time temperature monitoring is very important for High temperature superconducting cable's safe operation. The traditional cryogenic temperature sensors such as PT100 platinum resistance was vulnerable to the electromagnetic interference caused by the high voltage and large current in the HTS cables, which will affect the measurement accuracy. The optic fiber sensing technology has the advantages of anti-electromagnetic interference and be able to stand the high voltage. What's more, it can measure HTS cables' temperature continuously. In order to use it for the HTS cables' temperature monitoring, it's necessary to study its performance at low temperature.This paper carried a study on the most widely used optical fiber Bragg grating temperature sensor and distributed optical fiber temperature sensor which based on backward Raman scattering. The main work and research results are as follows:(1)We measured a temperature from 77 K to 296 k by using a bare fiber Bragg grating sensor and two others which are coated by different materials. By comparing their wavelength-temperature sensing characteristic curve in low temperature, we analysed the influence of coating materials to the property of sensors.(2)We studied the influence of packaging materials on temperature sensing properties by using three different fiber Bragg grating sensors to measure temperature between 77 K to 296 K. The gratings are all coated with the same material but one is not packed while the other two are packed with different materials.(3)We designed a heat-insulated container to make sure the experiment sample's temperature change steadily. Then we choose one whose temperature sensing properties is best from the five above-mentioned fiber Bragg grating sensors. we made an accurate calibration of this sensor through low temperature calibration experiment, achieving a practical calibration equation.(4) We measured the temperature between 77 K to 296 k by a distributed optical fiber temperature sensing system. We found that this system can measure the temperature accurately and steadily under low temperature through the comparison of PT-100 platinum resistance and theoretical result.The study in this paper shows that some coating materials can improve the temperature sensing properties of the fiber Bragg grating sensors at low temperature. It also proved that distributed optical fiber temperature sensor can measure the temperature accurately and steadily under low temperature, providing the theoretical basis for it's using in the high temperature superconducting cables' temperature monitoring.