The Atmospheric Sampler Based On DC Motor

With the continuous improvement of living standards, more and more air pollution problems come out. According to the World Health Organization published "World Health Report 2002" points out that indoor air pollution was a common problem, such as hypertension and high cholesterol and obesity as a major threat to human health 10. Meanwhile, indoor environmental experts point out: indoor pollution caused by decoration the pollutants volatile will be sustained release next 3-15 years. Therefore, the detection of indoor toxic gases becomes a very important mission, and the atmospheric sampling equipment begins to play a very important role.The key technology of the atmospheric sampling equipment is the gas flow measurement and control. This article introduces a new method of measuring gas flow, and using fuzzy control. The whole system has been successful.The atmospheric sampling equipment is composed of import, export, sampling pump, bumpers, speed detection circuit, the speed control circuit, MCU, keyboard, LCD and so on. Calculate air flow by measuring the motor's speed and voltage, using STC12C5410AD MCU. MCU control electrical current by controlling digital rheostat, and then achieve to control the gas flow rate. At the same time gas flow rate and sampling time can be shown on the LCD.This system solves the two key issues: the accurate measurement of gas flow rate, gas flow rate control.1. Flow rate measurementThe voltage of DC pump (Motor) contains the peak signal. After simulation filter, amplification circuit and the monostable chip, the counter of MCU can directly measure pulse number. As a result of pump's load capacity (the capacity of air is different by one lap of pump) changes, we need to add another parameter, which is the electrical voltage. Eventually achieve the purpose of measuring motor speed.Because there are maybe some noises in the signal, first signal should pass through digital filter before linearization. The system uses the filtering of median average, which integrates the advantages of median filtering and arithmetic average filtering. So it can filter the obvious noise, and eliminate random noise. In linearization, the traditional piecewise linear interpolation is not suitable, because this system contains two input parameters. So this system uses themathematical model of two-dimensional linear interpolation, it is a good solution to difficult problems because of linear multi-parameter. The way of two-dimensional linear interpolation calculates the output parameter using linear interpolation, by fixing one parameter. And then fix another parameter to linear interpolation.2. Control gas flow rateIn gas collected, the system automatically judge the difference between the real gas flow rate and the gas flow rate requested, and then two regarding error E and change EC of the error are as the fuzzy control system input. Use digital rheostat to change the current of the pump for achieving to control gas flow rate, and the pump can be stabilized at pre-set value.Traditional control methods are often from the view of the classical Math. Such as PID control of classical control theory needs to know the precise mathematical model, and then control rules are based on the mathematical model. However, in many cases it is very difficult to establish a precise mathematical model, and the parameters are time-variability, so it is difficult to control using traditional methods.Fuzzy just solve this problem. To establish the corresponding fuzzy control rules that is not only using the data sample database, but also according to human experience and reasoning methods. It is achieved to simulate the human brain to handle the collection of data. Using the fuzzy control as auto control, it is a good solution to deal the problem, that it is hard to establish a precise mathematical model the practical application. Because the analytical method simulates the human brain, the controlling accuracy greatly improves.In this system, the relationship between this pump and the gas flow rate is nonlinear, time-variability, so the fuzzy control is good for controlling flow rate. Experiments show that using the fuzzy control is a good solution to pump control. And the oscillation effect of the gas flow rate reduces greatly.This system uses new simple method to sample the gas flow rate, and MCU is low power consumption, low cost, high level of integration, which greatly reduces the overall cost. Due to the fuzzy control, it is achieved to control gas flow rate more stably, therefore the entire system has enormous application...