Design Of The Circuits For Tiny Displacement Measurement Based On Two-quadrant Silicon Photocell

Based on the technology of Nanjing University of Science and Technology on the detection of road damage, this paper concentrates on the design of tiny displacement measurement circuits, preparing for the practical application of the instrument of flatness.Through comparing different photodetectors, the paper chooses the cheap and simple one-silicon photocell as the detector of the system, and derives the formula of the system, from the formula we can find that the main target of the system is measuring the photocurrent of the photocell. After the introduction of the measuring method, do the whole design of optical structure:use the650nm-LD as the optical source to create round light beam, then paste an optical filter to the photocell to decrease the noise. Next, do the design of the processing circuits of photocurrent:set I/U conversion circuit to convert photocurrent to photovoltage, set Peak Detector circuit to keep the voltage at a high level for a second, set Analog to Digital Conversion circuit to convert analog signal to digital signal, and set UART circuit to communicate with the PC. At last, experiments will confirm the feasibility of the circuits and get the parameters of the system:when the distance of the target from the optical source is in the range of30cm-150cm, the measuring range of tiny displacement is-2.1mm to2.3mm, with a precision of10μm and a standard deviation of1μm.The paper comes up with a method to measure the tiny displacement using the two-quadrant silicon photocell, on the condition of having no influence on the precision of the system. The method will contribute to the cost reducing of the flatness instrument and, at the same time, do some good to the precision, Signal to Noise Ratio (SNR) and stability of the system.