Its working principle isThermoelectric effect。For example, a junction made of two different conductor materials can be generated at the junctionemf。The magnitude and direction of this electromotive force is related to the properties of two different conductor materials at the contact and the temperature difference at the two contacts.If these two different conductor materials are connected into a circuit, current will be generated in the circuit when the temperature at the two joints is different.This phenomenon is called thermoelectric effect orSeebeck effect。constituteThermoelectric coupleThe material of can be either metal orsemiconductor。Structurally, it can be a line or strip entity, or it can be usedVacuum deposition technologyorPhotolithographyMade of film.Solid thermocouple is mostly used for temperature measurement, and thin film thermocoupleThermoelectricThe stack (composed of many thermocouples in series) is often used to measure radiation, for example, to calibrate various light sources, measure various radiation quantitiesInfrared spectrophotometerorInfrared spectrometerRadiation receiving element, etc.[1]
Specific operation
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Thermocouples can be used to prevent the main gas valve from opening, or to close the main valve when the signal flame goes out.The hot end of the thermocouple is installed in the signal flame.Thermocouples can produce small currents.When the temperature controller contact is closed, the current generated by the thermocouple will open the pilot solenoid valve on the gas supply pipe.The solenoid pilot valve operates the main gas valve.In case of open circuit, the thermocouple generates a voltage of 30mV (1v is equal to 10130mV).The reading is 2mV higher or lower than this value, indicating that the thermocouple is damaged.The solenoid pilot valve shall operate at least 7mV.If the heating flame at the hot end goes out, as long as the solenoid coil works normally, it will lose its magnetic force within one minute.(However, some standards allow the system to be shut down for three minutes in domestic and small commercial units).It is better to use aluminum tube as the gas connection pipe of the signal flame (there will be peeling reaction in the copper tube).Electrolysis of aluminum tube must be prevented (usually with outer plastic protective sleeve).If the signal flame is too high (with adjusting screw), the thermocouple may be overheated and damaged.If the main burner flame contacts the thermocouple, it will be damaged.[2]
application
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Thermocouple circuit can generally measure temperature, and can also be used assensorUse.When the outside temperature changes, some control can be carried out.For example, control the water temperature,air temperatureEtc.
advantage
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Thermocouple is one of the most commonly used temperature detection elements in industry. The working principle of thermocouple is based on Seeback effect, that is, two ends of conductors with different components are connected into a loop. If the temperature of two connection ends is different, it will be generated in the loopThermal currentThe physical phenomenon of.Its advantages are:
① High measurement accuracy.Since the thermocouple is in direct contact with the measured object, it is not affected by the intermediate medium.
② Wide measuring range.Commonly used thermocouples can be continuously measured from - 50~+1600 ℃. Some special thermocouples can be measured to - 269 ℃ at least (such as gold iron nickel chromium) and+2800 ℃ at most (such as tungsten rhenium).
③ Simple structure and convenient use.Thermocouple is usually composed of two different types of metal wires, and is not limited by size and start. It is very convenient to use because it has a protective sleeve outside.[3]
