Since the materials of thermocouples are generally more expensive (especially when precious metals are used), and the distance between the temperature measurement point and the instrument is very long, in order to save thermocouple materials and reduce costs, compensation wires are usually used to connect the cold end of the thermocouple (free End) extend into the control room where the temperature is relatively stable and connect to the terminal of the instrument. It must be pointed out that the function of the thermocouple compensation wire is only to extend the hot electrode and move the cold end of the thermocouple to the instrument terminal of the control room. By itself, it cannot eliminate the influence of the temperature change of the cold end on the temperature measurement and cannot compensate. Therefore, other correction methods are needed to compensate for the influence of the cold junction temperature t0≠0°C on the temperature measurement. When using the thermocouple compensation wire, you must pay attention to the matching of the model, the polarity can not be wrong, and the temperature of the compensation wire and the thermocouple connection end can not exceed 100 ℃. Classification of temperature measuring instruments According to temperature measurement methods, temperature measuring instruments can be divided into two categories: contact and non-contact. Generally speaking, the contact temperature measuring instrument is relatively simple, reliable, and has high measurement accuracy; but because the temperature measuring element and the measured medium need to be fully thermally exchanged, it takes a certain time to reach thermal equilibrium, so there is a measurement The temperature delay phenomenon is also limited by high temperature resistant materials and cannot be used for very high temperature measurement. Non-contact instrument temperature measurement is based on the principle of thermal radiation to measure temperature. The temperature measurement element does not need to be in contact with the measured medium. The temperature measurement range is wide. It is not limited by the upper limit of temperature measurement and will not damage the temperature field of the measured object. , The response speed is generally relatively fast; but the measurement error is relatively large due to the influence of external factors such as the emissivity of the object, the measurement distance, smoke and moisture. Working principle of thermoelectric protection device 1. Components of thermoelectric protection device: mainly composed of thermocouple probe, wire, solenoid valve assembly and solenoid valve outer connecting rod. The thermocouple probe, wire, and joint are processed into a whole, the probe is fixed on the furnace head with a nut or a circlip, and the joint is connected with the solenoid valve connector; the solenoid valve assembly is composed of an electromagnet, a return spring, a gas valve and an outer connecting rod. It is installed in the casing of the combustion switch, and its control valve is connected in series in the air supply path. 2. Working principle: When the combustion switch of the stove is ignited, the thermocouple is heated to generate electromotive force, which supplies power to the electromagnet coil through the wire, so that the solenoid valve pressed down by the outer connecting rod when the combustion switch is turned on keeps the position, and the air communication is normal. combustion. When the furnace head is turned off due to some reason, the thermocouple probe cools down and loses the electromotive force, the electromagnet coil loses power, and the valve closes the gas circuit under the action of the return spring.
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