Introduction to Three Operating Principles of Thermostat

1、 Electronic thermostat
Working principle of electronic thermostat: dry thermostat, voltage divider composed of three 5k Ω resistors, which makes two internal comparators form a level trigger with an upper trigger level of 12UDD and a lower trigger level of 4UDD. Connect a reference power supply Uc to the 5-pin control terminal to change the upper and lower trigger level values. The output of comparator Al is connected to the input terminal of OR gate B1, and the output terminal of comparator A2 is connected to the input terminal of OR gate B2. Because the RS trigger composed of two OR gates must be triggered with a negative signal, the trigger signal applied to the 6 pin of the in-phase terminal of the comparator A1 will only flip when the potential is higher than the potential of the 5 pin of the inverted terminal; The trigger signal applied to the 2 pin of the inverting terminal of the comparator A2 only flips when the potential is lower than the potential 4UDD of the A2 in-phase terminal.
This electronic thermostat has a thermistor inserted in the center of the evaporator core like a capillary tube. The thermistor has a wire connected to the electronic circuit system. As the temperature decreases, the thermistor resistance increases. When the surface temperature of the evaporator is less than 4 ℃, the potential of the two legs is lower than 4V (that is, when a trigger signal is added), which will make the output terminal three legs high, and the relay coil cannot be conductive. Therefore, the compressor control circuit has no power, The electromagnetic clutch is disengaged; As the temperature rises, the resistance value of the thermistor decreases. When the surface temperature of the evaporator is greater than 4 ℃, the potential of pin 2 is higher than 4 V, and the potential of pin 6 is higher than 8 V (that is, when a trigger signal enters from the port), only then can the output terminal pin 3 have a low level output, and the relay coil is turned on. Therefore, the compressor control circuit is powered on, and the electromagnetic clutch is engaged.
2、 Bellows thermostat
The working principle of the bellows thermostat is shown in Figure 1. After a period of operation of the refrigeration system, the temperature in the vehicle gradually decreases, and the surface temperature of the evaporator gradually decreases. The sensor transmits low temperature to the bellows in the thermostat, which gradually contracts. When the temperature drops to a certain value, the bellows contracts to a certain extent, making the pressure of the bellows on the swing frame insufficient to overcome the tensile force of the extension spring, causing contact separation, circuit interruption, electromagnetic clutch disengagement, and compressor shutdown. When the temperature of the evaporator gradually rises, the bellows expands, pushing the frame to engage the contacts, and the compressor starts to operate again. This repeatedly prevents the evaporator from frosting and maintains a stable temperature in the vehicle.
In the thermostat, there is a set temperature adjusting screw connected to the cam. Turn the screw clockwise, and the extension spring is tightened. A relatively high temperature is required to close the contact, which means that the temperature in the vehicle is adjusted relatively high.
3、 Bimetal thermostat
Working principle of bimetal plate thermostat. This thermostat does not have a capillary tube, and the quartz colorimetric cell works directly by passing air through the surface. The manual temperature adjustment method of the pipette controller is the same as that of the bellows thermostat. Vortex mixer
A bimetallic sheet made of metals with different degrees of expansion and contraction in response to temperature changes has a moving contact on it and a fixed contact on the housing. Within the set temperature range, the bimetal sheet extends horizontally, the contacts are closed, the dry thermostat current is turned on, and the compressor electromagnetic clutch is engaged. Dry thermostat When cold air passes through the thermostat, it causes one of the bimetallic sheets in the thermostat to contract and form an arch. As the air temperature continues to drop, this piece of metal continues to contract until the contacts are separated, the circuit is interrupted, the electromagnetic clutch of the microplate oscillator is disengaged, and the compressor of the infrared inoculation ring sterilizer stops rotating. When the temperature of the thermostatic mixer gradually increases, the arc-shaped bimetal sheet of the micro centrifuge slowly straightens under heat, and the two contacts slowly converge together.