The thermostat is an electrical switching device that controls the temperature of an air-conditioned room. The temperature range in the air-conditioned room controlled by the thermostat is generally 18℃ - 28℃. Window air conditioning commonly used temperature controller is the principle of pressure to promote the contact of the on and off. Its structure consists of bellows, temperature-sensitive package (test tube), eccentric wheel, microswitch, etc., composed of a sealed induction system and a system to transfer the signal power.
The control method is generally divided into two kinds; one is controlled by the temperature change of the object to be cooled, mostly using vapor pressure type temperature controller, and the other is controlled by the temperature difference of the object to be cooled, mostly using electronic temperature controller. Thermostat is divided into:
Mechanical type is divided into: vapor pressure type thermostat, liquid expansion type thermostat, gas adsorption type thermostat, metal expansion type thermostat.
The vapor pressure thermostat is divided into: inflatable, liquid-gas hybrid and liquid-filled. Household air conditioning mechanical type are dominated by this type of thermostat.
Electronic type is divided into: resistance thermostat and thermocouple thermostat.
The role of the circuit system:
The role of the circuit system of the air conditioner is to control the normal and multi-functional operation of the air conditioner, to protect the compressor and fan motor normal operation. The components of the circuit system are mainly: temperature controller, thermal protector, main control switch, running capacitor, fan motor running capacitor, etc. are fixed in the control box. The figure on the left shows the electrical circuit diagram of a single-cooled air conditioner. The function of the temperature controller is only to control the start and stop of the compressor.
Principle of operation
Vapor pressure type
The action of the bellows acts on the spring, whose elasticity is controlled by the knob on the control board, and the capillary tube is placed in the air outlet of the indoor suction air of the air conditioning unit to react to the temperature of the indoor circulating return air. When the room temperature rises to the set temperature, the capillary tube and bellows in the temperature-sensitive agent gas expansion, so that the bellows elongation and overcome the spring elasticity of the switch contacts on, the compressor is running, the system refrigeration, until the room temperature falls to the set temperature, the temperature-sensitive package of gas contraction, bellows contraction and the spring with the action of the switch is placed in the off position, so that the compressor motor circuit is cut off. This repeated action, so as to achieve the purpose of controlling the room temperature.
Electronic temperature controller
Electronic temperature controller (resistive) is the use of resistance to measure the method of temperature sensing, generally using platinum wire, copper wire, tungsten wire, and semiconductor (thermistor, etc.) for the temperature measurement resistance, these resistors have their own advantages and points. Most of the sensors for home air conditioners are thermistor type.
Thermistor thermostat is made according to the principle of Whisden bridge, (left) is the Whisden bridge. At both ends of the BD connected to the power supply E, according to Kirchhoff's law, when the resistance of the bridge R1 × R4 = R2 × R3, A and C two points of the potential is equal, no current flows between the output A and C. The size of the impedance R1 of the thermistor changes with the rise or fall of the surrounding temperature, so that the equilibrium is disturbed, and there is an output current between AC. Therefore, when constituting a thermostat, the temperature adjustment range and operating temperature can be easily changed by selecting an appropriate thermistor
Metal Expansion Thermostat:
Based on the principle of heat rise and cold contraction of an object. Thermal expansion and contraction is the object of the **** nature, but the degree of its thermal expansion and contraction of different objects is not the same. The two sides of the double gold sheet is a conductor of different substances, in the changing temperature due to the degree of expansion and contraction is not the same and make the double gold sheet bending, touching the set contacts or switches, so that the set circuit (protection) began to work.