KEYWORDS: Error analysis, Resistance, Power supplies, Resistors, Control systems, Transistors, Water quality, Design, Analog electronics, Temperature metrology
In the field of water quality monitoring, it is frequently necessary to convert water quality parameters into electrical signals for long-distance transmission, voltage signal transmission is susceptible to interference from line impedance and environmental electromagnetic noise, consequently, current signals with robust anti-interference capabilities are commonly employed for transmission purposes. However, changes in power supply voltage, ambient temperature, and load resistance still affect the accuracy of output current. Regarding these issues, this paper presents a design based on PID control for a 4~20mA constant current source. Obtain the actual output current value through a sampling circuit, when the actual current value deviates from the set value, adjust the D/A output voltage through an incremental PID algorithm to make the actual output current value consistent with the set value. Finally, experiments were conducted to verify that the relative error of the output current is less than 0.03% when the power supply voltage, ambient temperature, and load resistance change.
The issue of AQI is a hot topic of public concern today and monitoring the main pollutants in the air is a prerequisite for addressing AQI issues. Research has shown that CO plays a major role in AQI and accurate monitoring of CO concentration in the air is particularly important. CO monitoring generally uses MQ-7 sensors, which needs to solve the problems of sensitive body resistance heating and temperature and humidity compensation during use. In response to these problems, a hardware compensation circuit with dual power supply cycle rotation heating is designed in this paper. At the same time, temperature and humidity data in the tested environment is obtained through the sensor. Based on the temperature and humidity characteristics of MQ-7, software compensation is used to improve its monitoring accuracy. Finally the article verifies through experiments that this method can make MQ-7 not affected by temperature and humidity, and accurately monitor the CO content in the air.
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