Signal processing circuit design of particle sensor on light scattering particle concentration theory

Particle concentration detection sensor which is based on light scattering particle concentration theory has high reliability, fast and easy using and so on. However, it demands to extract the small signal in the background of the large noise. It requires to use the modulated light source, so this paper design the circuit, it uses the digital multiplier and make the sensor work more steady and more fast. Tirst the signal goes through the preamplifier circuit, then goes through the six-order band-pass filter, the last the band limited weak signal should be locked by lock-in amplifier. The paper offers the good method to detect the weak signal in the big noise ground.