Fig. 1. Structure of pressure and temperature sensors. (a) Schematic diagram; (b) physical map

Fig. 2. Relationship between FBG wavelength and temperature

Fig. 3. Pressure calibration results of the sensor

Fig. 4. Relationship between pressure sensitivity and temperature

Fig. 5. Relationship between EFPI cavity length and temperature under normal pressure

Fig. 6. Principle of the downhole monitoring system

Fig. 7. Principle of monitoring instrument and spectrum of sensor

Fig. 8. Test results of cavity length resolution

Fig. 9. Long-term online test results in downhole

Fig. 10. Test results of shut-in operation

Fig. 11. Short-term pressure monitoring results with high resolution