Principle and control method of electronic thermostat

There are generally two control methods; one is controlled by the temperature change of the object to be cooled, mostly using a vapor pressure temperature controller, and the other is controlled by the temperature difference of the object to be cooled, mostly using electronic temperature Controller. The thermostat is divided into:
　　Mechanical type is divided into: steam pressure type thermostat, liquid expansion type thermostat, gas adsorption type thermostat, metal expansion type thermostat.
　　The vapor pressure type thermostat is divided into: inflatable type, liquid-gas mixed type and liquid-filled type. The mechanical type of household air conditioner is mainly based on this kind of thermostat.
　　Electronic type is divided into: resistance thermostat and thermocouple thermostat.
　　The role of the circuit system:
　　The function of the air conditioner circuit system is to control the normal and multi-function operation of the air conditioner, and to protect the normal operation of the compressor and fan motors. The main components of the circuit system are: thermostat, thermal protector, main control switch, running capacitor, fan motor running capacitor, etc. are fixed in the control box. The picture on the left is the electrical circuit diagram of the single-cooling air conditioner. The function of the temperature controller is only to control the start and stop of the compressor.
  working principle
　　 steam pressure type
The action of the bellows acts on the spring. The elastic force of the spring is controlled by the knob on the control panel. The capillary tube is placed at the air inlet of the air conditioner and reacts to the temperature of the indoor circulating air. When the room temperature rises to the set temperature, the temperature-sensing agent gas in the capillary tube and the bellows expands, causing the bellows to extend and overcome the elastic force of the spring to connect the switch contacts. At this time, the compressor runs and the system cools until room temperature. When it drops to the set temperature again, the gas in the temperature sensing bulb shrinks, and the bellows shrinks and acts together with the spring. The switch is placed in the off position to cut off the motor circuit of the compressor. Repeated actions to achieve the purpose of controlling the room temperature.
　　Electronic temperature controller
The electronic temperature controller (resistance type) is measured by the method of resistance temperature sensing. Generally, platinum wire, copper wire, tungsten wire and semiconductor (thermistor, etc.) are used as temperature measuring resistors. Each of these resistances has its own advantages. point. The sensors of household air conditioners are mostly thermistor type.
　　 Thermistor type thermostat is made according to the principle of Wheatstone bridge, (left picture) is Wheatstone bridge. Connect power E at both ends of BD. According to Kirchhoff’s law, when the resistance of the bridge is R1×R4=R2×R3, the potentials of A and C are equal, and no current flows between the output terminals A and C. , The size of the thermistor's resistance R1 changes with the rise or fall of the surrounding temperature, so that the balance is destroyed, and there is an output current between AC. Therefore, when constructing the thermostat, it is easy to change the temperature adjustment range and working temperature by selecting the appropriate thermistor
　　Metal expansion thermostat:
　　According to the principle of thermal expansion and contraction of objects. Thermal expansion and contraction are common to objects, but different objects have different degrees of thermal expansion and contraction. The two sides of the double sequin are conductors of different materials. Under the changing temperature, the double sequin is bent due to the different degree of expansion and contraction. When it touches the set contact or switch, the set circuit (protection) starts to work. Temperature control switch, thermostat, thermal protector