| For their advantages of small size,simple construction and anti-electromagnetic interference,etc.,fiber-optic Fabry-Perot(F-P)sensors have been widely used in sensing and measurement of various physical quantities such as temperature and pressure.However,in real pressure sensing at various environments,the cross-sensitivity of temperature on pressure is always an issue.the temperature needs to be measured simultaneously for pressure compensation.The need for dual-parameter measurements based on fibre-optic F-P sensors technology are becoming more and more urgent,while demodulation techniques for such sensors have received increasing attentions.Therefore,a non-scanning correlation demodulation scheme based on dual-segment optical wedge is proposed in this paper.The demodulation scheme adopts the combination of dual-segment optical wedge and linear CCD to realize the pressure-temperature dual-parameter measurement based on the compound fiber F-P sensor.The detailed research contents are as below:First,starting from the dual-parameter measurement requirements of the compound fiber F-P sensor,by comparing and analyzing advantages and disadvantages of several common demodulation techniques,a non-scanning correlation demodulation scheme based on dual-segment optical wedge is proposed.Based on this demodulation scheme,the corresponding mathematical model is established,and the correlation interferometric signal output from the system is simulated using this mathematical model to verify the feasibility of the demodulation scheme.Secondly,an SLED broadband light source is used as the system light source,and a combination of a small-aperture fibre collimator and a Powell prism is selected as the linear spot shaping device,then a two-segment optical wedge structure with different inclination angles and thickness ranges is used as the correlation interference signal generator according to the variation range of the optical thickness of each cavity of the compound fibre-optic F-P sensors.The optical path of the system is constructed.Then,according to the characteristics and performance requirements of the output signal of the non-scanning correlation demodulation system based on dual-segment optical wedge,the corresponding hardware circuit and demodulation algorithm are designed,and the line array CCD is driven by the FPGA control circuit to convert the correlation interferometric signal from optical signal to voltage signal,and the resulting voltage signal is input into the AD conversion circuit to output in the form of digital signal.The output signal enters the FPGA control circuit written with the demodulation algorithm for demodulation.Due to the presence of high and low frequency noise in the output signal,the peak position of the signal cannot be accurately obtained,therefore,by designing a reasonable demodulation algorithm,the pixel sequence number corresponding to the peak position of the correlation interferometric signal is accurately extracted,and the result is transmitted to the host computer for display through the serial communication circuit,completing the demodulation system circuit and algorithm design.Finally,an experimental setup for temperature-pressure dual-parameter measurement based on the non-scanning correlation demodulation system of dual-segment optical wedge was built to perform pressure-temperature tests on a compound fibre-optic F-P sensor with an 80-?m vacuum cavity and a 680-?m substrate cavity.A pressure sensitivity of-23.357/MPa,a temperature sensitivity of-0.226/?,and a temperature-to-pressure cross-sensitivity of 0.019/? in the pressure range of 0.1-3.0MPa and temperature range of 50-350? were realized.And By temperature compensation of the pressure measurements,the error between the corrected pressure and the reference pressure was less than 0.02 MPa. |
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