System Design On Extending Dynamic Range Of Transmittance Meter

As one of the important elements of meteorological,visibility reflects the degree of atmospheric pollution near surface.The measurement of visibility can be applied in meteorology,aviation,navigation,traffic departments,and has a significant impact on the laser communication,image transmission.It has practical significance and application value that how to extend the dynamic range of transmittance meter,because the dynamic range of transmittance meter directly determines the measurement range of visibility.At present,automatic gain control is chosen,the main method to extend dynamic range.It takes advantage of the circuit feedback to regulate circuit gain automatically by selecting different resistance through a series of switch.However,electronic noise of automatic gain control has a great influence on the measuring system,and brings the system into a measurement error.Meanwhile,receiving optical signal makes detector generate nonlinear effects or saturation,and can damage photoelectric detector.In this paper,it combines a motor and a neutral density filter to ensure the accuracy of measurement system by reducing the received optical signal intensity.It not only can hardly increase the electronic noise,but also protect the photoelectric detector in a way.The result shows that:system's dynamic range is extended 0.6 times,when use neutral density attenuator whose transmittance is 40%.And it is extended 6.3 times when the transmittance is 87%.At the time,we arrived at the following conclusion:(1)The way of combining with motor and neutral density filter will not bring electronic noise compared to the change of feedback resistor to extend dynamic range of system;(2)It reduces the uncertainty of system due to the photoelectric detector's nonlinearity or saturation by using filters;(3)By choosing different transmittance of neutral density attenuator,the system's dynamic range can be flexibly extended.