Research On The Demodulation System Of Groundwater Temperature And Pressure Dual-detection Fiber-optic Sensor

Optical fiber sensors have the advantages of small size,light weight,anti-interference,and anti-corrosion.They are widely used in geological prospecting,oil exploration,mine monitoring and other fields to realize temperature,pressure,vibration and other parameters.However,the demodulation equipment of the optical fiber sensor has problems such as expensive price,large space occupation,low demodulation accuracy,and poor stability.Aiming at the problem of low demodulation performance and weak stability of the dual-check fiber optic sensor for geological exploration borehole water temperature and water pressure,a demodulation method based on a tunable laser is studied and implemented to improve the demodulation performance of the fiber demodulation system.The demodulation circuit includes modules such as power supply,light source drive,photoelectric conversion and acquisition,control and communication.Through the simulation and comparison of two different current control circuits,the method of voltage conversion into constant current is selected to drive the light source,and the stability of the current output is verified;combined with the laser's internal semiconductor cooler,the temperature control circuit is designed to ensure that the laser can operate Work stably at the right temperature.For the photoelectric conversion module,the diode is designed to work in photovoltaic mode to reduce the influence of dark current in the conversion process.The demodulation process includes the calibration of the laser wavelength,the demodulation algorithm and the design of the host computer.The calibration of the laser is used to realize the correspondence between the current and the wavelength.The current is output through the D/A chip,and the laser is driven to emit the corresponding light wave.The demodulation algorithm uses the power weighting method,first collects the original data through the A/D chip,and uses the cumulative average method to reduce the noise of the data to reduce the interference to the peak,and then set the threshold to improve the accuracy of peak finding and reduce the amount of calculation,Take the power of the sampling point as a weighting coefficient and multiply the corresponding wavelength and then accumulate,then take the average value,and finally determine the position of the peak.The design of the host computer adopts C#language to display the demodulated data result,and can complete the threshold setting and other operations.The performance of the demodulation system is verified by performing calibration tests on the temperature and pressure of the sensor.The test results show that the demodulation range of the fiber demodulation system realized in this paper is 40nm,the demodulation accuracy is±3pm,the demodulation time is 1s,and the performance is relatively stable.The demodulated wavelength fluctuation is 2pm in the temperature range of 30?70? The demodulated wavelength fluctuation is 2pm in the pressure range of 0?5MPa,and the linearity between the parameter and the wavelength is high,which can meet the real-time detection and long-term demodulation of the two parameters of temperature and pressure,and can be applied to groundwater temperature and pressure monitoring.Figure 87 table 10 reference 69...