The Study On Long-term Stability Of Fiber EFPI Pressure Sensor

Fiber optic sensor used in oil Wells for temperature and pressure monitoring is immune to electromagnetic interference and can withstand the extreme conditions, including high temperature and high pressure (above lOOMPa). The sensor scan be used for accurately real-time monitoring and provide dynamic real-time temperature so that oil companies and service companies give them universal attention and researsh. But when the fiber EFPI sensor applied to high temperature and pressure environment, the liquid molecules will penetrate into the defects of quartz material so that the volume of the quartz structure of the sensor will expand and the cavity length of fiber EFPI pressure sensor will increase, which defects the long-term stability of fiber EFPI pressure sensor. Therefore, how to ensure the long-term stability of fiber EFPI pressure sensor is an urgent problem.Fully draw on the basis of previous research, this paper gives a systemic, detailed study on the long-term stability of fiber EFPI pressure sensor under high temperature and pressure. The development of long-term stability of fiber optic sensor is introduced briefly, and the reasons for poor stability of fiber EFPI pressure sensor are analyzed. Based on the survey of the stability techniques of the fiber EFPI pressure sensor, it is concluded that a carbon layer coated on the fiber EFPI sensor could provide an effective protection. According to the comparison of the carbon coating methods, the laser induced chemical vapor deposition is theoretically analyzed and experimentally studied. A complete set of laser induced chemical vapor deposition system is designed and constructed. Through optimization of the carbon-coating parameters, the coated fiber EFPI pressure sensor shows a fairly good stability in 72Mpa and 300℃environment in near one year's operation. The experiment results indicate that the sensor can meet the needs of high repeatability, high accuracy and long-term stability under the pressure range of 0-72MPa and the temperature 300℃, which is high value for industrial applications.