Development Of New Large Flow Laser Particle Counter

Light-Scattering Particle Counter is a kind of monitor equipment usually used in mea-suring the cleanliness of clean-rooms. It can figure out the number of particles in different diameters, it can also work out the cleanliness of clean-rooms via the numbers. Nowadays, It is common for overseas'particle counter that all of them have intellectualized operating system, friendly man-machine interface and characteristic of high sensitivity and large flow. Meanwhile, they are stepping on the way to networking. To compare with it, our home-made particle counters' sensitivity and flow is low; their man-machine interface is made by LCD or LED and keyboard, which is hard for users to operate. Also, the standard they use is too old to be in accordance with the provisions of new standard and to meet with the need of home industry.This article discuss the determination and definition of cleanliness and the method of measurement in the newest standard ISO 14644, and determine the working principle of particle counter, on the base of analyzing the sensor's output signal, we design a new large flow particle counter which contains signal range differentiate system, digital process system, man-machine interaction system and operating system. We use different magnification and Noise filtering to raise the signal and noise ratio of the particle signal, and to solve the error of omission which caused by the huge difference of the signal range between different particles. We design a high-speed Schmidt comparator circuit and count signal processing circuit realized by Verilog HDL. And we select the Schmidt circuit with hysteresis voltage tolerance properly, the electric pulse signal high frequency noise caused by the residual gauge and the wrong gauge phenomenon are completely eliminated. We select ARM micro controller and touch screen LCM as the realization of human-computer interaction system, because of the ARM microcontroller's hardware resources, high working frequency, the particle counter interface will be more friendly; we design the more powerful operating system which include parameter settings, particle measurement, data reading and data observation and other function; we manufacture the prototype, using the latest international standard ISO 14644 to calculate clean room cleanliness, pump flow rate reaches 50L/min, which can improve the efficiency of counter measure. With imported equipment LASERIII comparative experiments, we confirmed the new large flow particle counter with stable and reliable performance, perfect function, has very high practical value, narrowing the gap of domestic and foreign particle counter.