The Key Technology Of Two-dimensional Structure Deformation Monitoring System Based On PSD

The structural deformation is an important parameter to assess the health state oflarge buildings such as bridge. The methods to measure structural deformation arevaried, among which the imaging method is widely used due to the advantages likewide measuring range, non-contact measurement, relatively low costs, suitable tolong-term dynamic monitoring for two dimensional deformation etc. However, theresolution and accuracy of structural deformation monitoring system based on CCDimaging is limited by the CCD pixel and its complex signal processing way. It will bepossible to overcome these shortcomings by using continuous device PSD instead ofCCD, because of PSD’s advantages, such as high resolution, simple signal processingand continuous measurement. For bridge structural deformation, however, there arepoor working conditions and complex background light. And it is harder to ensureenough radiation flux of the light spot on PSD as a result of long distance measurement.Those factors will have an effect on displacement measurement based on PSD. Toobtain high precision structural deformation measurement. the factors effecting themeasuring precision are analyzed systematically in this paper, Then the correspondingsolution methods are presented to decrease or eliminate influences of some factors,which are modeled in theory. According to those theoretical studies, the appropriatedevices can be selected to design the preliminary system. The main research is asfollows:①Based on the position principle and signal processing methods of PSD, amathematical model for measurement deviation is set up. The influences of spotintensity, background light, electrical noise on the measurement accuracy are analyzed.According to the characteristics of background light, such as strong light intensity,variety, various wavelengths, it can be eliminated effectively after driving the lightsource by pulse modulation and using optical filter.Then the measurement deviationmodel can be simplified, whose correctness is verified by some experiments.②The relationship between the radiation flux of light spot and the light intensity oflight source is presented based on the light path in the optical system. According to themeasurement deviation model and the accuracy requirement of this system, theminimum light intensity of displacement measurement based on PSD is determined,which provides a theoretical basis for the design of the light source. ③The self-calibration technology of the CCD imaging method is analyzed first.And the difference between the PSD and CCD location is studied. Then dual-frequencypulse modulation is raised for self-calibration of this system with the correspondinglight source and control circuitry, according to the features of PSD location.④Based on the analysis and solutions of the key questions, the preliminary designof the system hardware and software has been completed. The hardware includesphotoelectric detection circuit and optical system, while the software includes dataacquisition, data processing, and human-computer interaction software.⑤Two experiments which are calibration experiment and measurement experimenthave been done under laboratory conditions. Results show that there is relative error0.62%between the magnification obtained by experiment and the theoretical value,suggesting that the self-calibration technology is valid. The precision and linearity ofdisplacement measurement are4μm and0.15%respectively. Thus, PSD measurementsystem has better resolution and accuracy than the system based on CCD imagingmethod does.