Study On Fiber-Optic Strain Measurement System Based On Laser Pulse Time-Interval Method

Summarizing the development statement of monitoring technology for bridge, based on principle of pulse laser ranger detection and fiber-optic strain measurement, in view of the problem affected by single-chip inherent feature, integrating the goodness of CPLD device and single-chip, using A/D converter to measure the count quantization error, a strain measurement system is worked out.The above system chiefly consists of light source, optic fiber sensor, photo detector and signal processing circuit. In the design of optical system, to improve system precision, the fiber optic coupler is added to make a laser pulse circle; in the unit of photo detection, we make a high-precision temperature compensation APD bias circuit, which allows system to abate the noise caused by temperature changer and dark current. In signal processing circuit, the key of our study, based on methods of MCU+CPLD and A/D converter, a time interval measurement unit is done, in which an ISP CPLD counter is carried out to judge laser pulse for controlling counting and offering signal of time series and control, and a count quantization error measurement circuit which main ramp circuit and 12 bits A/D conversion circuit guarantees the resolution of system. During systematic design, as for each section of optical system and signal processing, theory analysis and the optimal selection of components are finished, on the basis of which the simulation in some relative parts of system is analyzed and the evaluation of systematic performances is completed. Thereafter with different length, stain measurement experiment setting is constructed, whereby two group experiments is carried out. The result of experiment shows that high precision, super sensitivity and target resolution have been achieved by elaborate design and rational method; furthermore the system possesses good adaptation to different measuring environment.