Industrial Humidity Control System Based On MCU

Industrial humidifier is essential instrument in fields like meteorology, hydrology, medical science, biology, storage and production sections, agriculture and forestry etc. The traditional Industrial humidifier usually uses high pressure atomizer, wet media, steam humidifier, spinning disk humidifier and electric steam humidifier as humidifying tools. Most of these humidifiers are bulky, expensive and with lower conversion efficiency, their control method are semi-intelligent that the effluent needed to be evacuated artificially, so that the artificial record system fails more frequently and the humidity control accuracy is lower.Based on the above reasons, we began the research for intelligent industrial humidity control system. Our intelligent humidity control system is based on PC SST89E564 which is mainly composed of digital MCU, water tank, lift pump, filter, humidifier, sensors, reverse osmosis membrane etc. Tap-water from outside goes through the filter, reverse osmosis membrane, water tank, and then goes into the ultrasonic humidifier. The digital control unit consists mainly of key display module, pressure and humidity acquisition module and the output control module, etc.Firstly, the key display module provides a way for human-computer interaction. The users can set the parameters in advance by keyboard, such as the system time, drainage time etc. Then the LCD display module can display the time and humidity values, system work instructions, power, control system fault instructions, and water level, water producing and stopping state.The pressure sensor is mainly used to detect external water information. When the external tap-water stops, the system must be cut out to protect the pump. Since the wastewater produced from the filter and reverse osmosis membrane unit of the system must be discharged, therefore, an electromagnetic valve is designed to control the effluent discharge.In order to detect the water level in the water tank, two floaters are adopted in the system. When the water level is high, the pump will stop working. When the water level is too low, the pump will begin to pump water to the tank. Another water level sensor is installed in the water tank. When the water level is too low, it indicates that something is wrong with the water supply system, and then the power must be cut off to protect the system equipments.The high humidity control precision is one of our key researches, so that a highly precise humidity sensor HM1500 is chosen as a period test unit in the system. The sensor has the following features: (1) the humidity measurement range is 5% to 99% (relative humidity); (2) the working temperature is between - 30℃and 60℃; (3) the response time is about 5s faster; (4) a coat outside makes it possible to work in hostile environments; (5) the output voltage and humidity linearity is high.The output voltage detection circuit of the sensor adopts the highly precise Successive approximation A/D converter which uses the ADC0809 as analog-digital conversion unit. The software adopted the PID control algorithm which is widely applied in industrial control. The algorithm has a very simple structure, good robustness and high reliability, easy parameter setting, etc, which is also forming the foundation for high-precision humidity control.The ultrasonic humidifier frequently used in foreign countries is adopted in the system. The sensor is in no need of mechanical drive and works without noise interference, and is pollution-free, with low failure rate, low energy consumption, high efficiency and convenient maintenance atomization, reliable. Also, it can be used in larger space to provide equality of humidity, and provide local temperature compensation for specific part of special space, so the sensor is very flexible. Because the working environment might be very severe, the power supply can be easily disturbed, so we use a special power monitoring and the reset chip MAX708 to detect the 12V power supply. Once the power fluctuations that can cause the system restoration are found, the key equipments such as pump in the system will be firstly cut off for the electricity protection, and then the current situation will be recorded and saved for system fault diagnosis later.Through repeating tests, the system has achieved the basic functions of intelligent controller like timing drainage, automatic pumping and highly precise humidity control, at the same time, the system is with low cost, high efficiency and high automation degree.At the end of this thesis we have a conclusion about the disadvantage of the system design and improvement methods, making a preparation for further research.