Laser Dust Particle Counter Automatic Flow Control System Design

When the supply voltage of an induction motor was changed, its power will produce a corresponding change. Based on this principle, an investigation of the real-time monitor and control procedure for the sample flow was carried out and a system was explored which included a real-time monitor module and automatic control module in the present work.The hardware of this system was mainly consisted of the Silicon Controlled Rectifier (SCR), a heat mass flow meter, a Liquid Crystal Module (LCM) and an ARM processor, in which the ARM processor was the core unit of the system.The output signal from AOPC was converted by the ARM internal ADC (Analog-to-Digital Convert) module. Based on the AOPC output characteristics curves, the sample volume information was got, and then sent to the LCM for display. Eventually, the real-time monitor was accomplished.According to the feedback signal from the mass flow meter, with the SRC changing the supply voltage of the pump(the control variables), the sample flow volume was controlled on the basis of the theory of SCR adjusting the voltage and timing. The incremental PID automatic control algorithm was selected to achieve the automatic control of the sample volume, which determined the change of the phase on the basis of deviation amount, deviation accumulation and deviation changing rate.Test results predicate that the system presented can provide a real-time display and a rapid and accurate control of the sample volume. As a50LPM flow was controlled, it could be stable and accurate in10s, while average error was in the range of±0.1%during a long-term stable operation, which is far superior to the requirement of ISO21501-4and JJF1190-2008.