The air conditioning and refrigeration course in Luoyang Electromechanical School has always been taught by hands and teachers one-on-one.

The indoor ambient temperature sensor provides the room temperature to the CPU and compares it with the temperature set by the remote controller to control the operation and stop of the air conditioner; The indoor tube temperature sensor provides the evaporator temperature to the CPU to protect the shutdown when the refrigeration system enters an abnormal state.

Ambient temperature sensor room, lower bias resistor r 17(8. 1kω precision resistor), diodes D 1 1 and D 12, electrolytic capacitor E5, ceramic chip capacitor C7, resistor R 19 and CPU⑤. The pipeline temperature sensor pipeline, lower bias resistor r 18(8. 1kω precision resistor), diodes D 13 and D 14, electrolytic capacitor E6, ceramic capacitor C8, resistor R20 and CPU⑥ pin constitute the pipeline temperature sensor circuit.

The working principle of loop temperature sensor and tube temperature sensor is the same. Take the loop temperature sensor as an example. The loop temperature sensor (negative temperature coefficient) and the resistor R 17 form a voltage dividing circuit, and the calculation formula of the voltage across R 17, that is, the pin voltage of CPU⑤, is 5×R 17/ (loop temperature sensor resistance+R17); The resistance of the ambient temperature sensor changes with the change of room temperature, and the voltage at the pin of CPU⑤ also changes. The ambient temperature sensor has corresponding resistance at different temperatures, and the pin ⑤ of CPU has corresponding voltage value. The room temperature is proportional to the ⑤ pin of the CPU, and the CPU calculates the actual room temperature according to different voltage values.

Midea air conditioner's ambient temperature and pipe temperature sensors are both 25℃/10Ω. The resistance of the sensor is10Ω at 25℃ and16.10Ω at 15℃. The temperature resistance of the sensor corresponds to the voltage of the CPU pin.