Analog instrument automatic control

Automatic control of air-conditioning refers to the function of air-conditioning (referred to as air-conditioning) to keep the environmental state parameters in the space (such as buildings, trains, airplanes, etc.) at desired values under the conditions of outdoor climate conditions and indoor load changes. The automatic control of air-conditioning is to maintain the air-conditioning system in an optimal working state through the automatic detection and adjustment of air condition parameters and to maintain the safety of equipment and buildings through safety protection devices. The main environmental parameters include temperature, humidity, cleanliness, flow rate, pressure and composition.

To control the air conditioning system, its control functions mainly include:
1. Temperature and humidity monitoring. That is to monitor the temperature and humidity of the fresh air, return air and exhaust air to provide a basis for the adjustment of the system temperature and humidity.
2. Control of the air valve. That is, the on-off control or analog adjustment of the fresh air valve and the return air valve.
3. Adjustment of cold/hot water valve. That is, the opening of the valve is adjusted according to the temperature difference between the measured temperature and the set temperature to keep the temperature difference within the accuracy range.
4. Control of humidification valve. That is, when the air humidity is lower than the set lower limit or exceeds the upper limit, the opening and closing of the humidification valve are controlled respectively.
5. Fan control. That is to realize the start-stop control or frequency conversion speed control of the fan.

Due to its mature theory, simple structure, low investment, easy adjustment and other factors, analog control instruments have been widely used in air conditioning, cold and heat sources, water supply and drainage systems in the past. Generally, analog controllers are electric or electronic, with only hardware part, no software support. Therefore, it is relatively simple to adjust and put into operation. Its composition is generally a single-loop control system, which can only be applied to small-scale air-conditioning systems.