Multiplexed Fiber-Optic Pressure and Temperature Sensor System for Down-Hole Measurement

A fiber Fabry-Perot (F-P) interferometer and a fiber Bragg grating (FBG) based pressure and temperature multiplexing sensor system is presented. This system is designed for high-temperature oil well down-hole permanent monitoring of pressure and temperature. Connecting a FBG temperature sensor and a F-P pressure sensor in series in the sensor head, the sensor system combines the advantages of simple structure of FBG for temperature sensing and high accuracy and low-temperature cross-sensitivity of F-P pressure sensor. Experimental results showed that the temperature measurement accuracy of 0.5degC and the long-term drift of the air gap of the F-P pressure sensor at 300degC is less than 0.1% within 300 h time span. This indicates that a long-term pressure measured accuracy of 0.03 MPa has been achieved in pressure gauge range of 0-30 MPa and in temperature variation range between 18degC to 300degC.