The Design Of The Foreword Scattering Visibility Meter Based On ARM

Atmospheric Visibility is a target which is reflected the transparency of atmosphere and is the conventional project of the meteorological observation .Visibility is important to the navigation, the aviation, on land transportation as well as the military activity and so on .At present, there are only a few portable and high accurate visibility meters which are used in bad circumstance of the sea,we need design the visibility meter which is fit for the measurement on the sea.On the basis of Atmospheric Visibility theory , this article has studied the key technology of visibility examination system, the key technology mainly includes the stability of the photosource , the phase sensitive technology of weak signal and the signal antijamming technology and so on. This system is made up of the launch module, the receive module, the signal processing module and the power source module and so on. The measurement of atmospheric visibility belongs to the weak signal examination technology, it is easy to receive disturbance from the outside natural light and other environmental factor, therefore how to filter a number of disturbance and pick up the useful weak signal is the core of the design. Firstly, this article has designed the optical system of the launch module and the receive module, and the modulation design of the launch photosource , the design of photo electricity receiver,the amplifier circuit ,the band pass filter circuit and the phase-lock amplifier. This article has studied the photosensitive examination technology and the phase-lock amplifier technology which is fit to detect the weak signal. This article has designed the circuit of the photosensitive examination which is made up of OPT101 as the core ,the design enhances the examination sensitivity and the antijamming ability ,the circuit has been simplified; this article also has designed Balanced Modulator Demodulator AD630 as the core of the phase-lock amplifier circuit and Phase Shifter which is made up of Dual D-type flip-flop trigger SN74HCT74 and Dual Retriggerable Monostable Multivibrator M74HC4538B1R , the experiment proved that, under the big noise background, this circuit can pick up the useful signal which reflected the change of visibility. The direct-current signal after the phase-lock amplifier circuit is inputed into microprocessor ARM after the AD processing,and finally obtains the visibility value after the theory operation. In order to guarantee the stability of the system, especially the adverse circumstance of the sea, the design is sealed and guarded against salty, fog and water, such as carrying on the coating to the lens and so on.Finally , the visibility meter is designed.