Thermocouples are widely used in industrial and numerous types, can satisfy diversified customers' needs. The pt100 thermocouple is industry for the commonly used one kind of temperature sensor, it with metal platinum resistance change with temperature, the principle of work. The principle of pt100 thermocouple pt100 thermocouple, it is directly proportional to the change of resistance with temperature. Pt100 resistance and temperature variation relationship is: when pt100 temperature 0 ℃ its resistance of 100 ohms, at 100 ℃ its resistance value is about 138. 5 ohms. Its industrial principle when pt100 at 0 degrees Celsius when his resistance of 100 ohms, pt100 thermocouple its resistance into uniform growth as temperatures rise. Metal thermocouple resistance value and temperature can use the following general approximate relation said, namely the rt = rt0 [ 1 +α( t- t0) ] Type of rt for temperature t resistance; Rt0 for temperature t0 ( Usually t0 = 0 ℃) When the corresponding resistance; Alpha for temperature coefficient. Relationship between resistance and temperature of semiconductor thermistor for rt = aeb in rt for temperature for t/t type of resistance; A and b depends on the structure of the semiconductor material constant. Pt100 is more than about the principle of thermocouple, hoped everybody before use this principle to master, can effectively help you better use of thermocouple. Pt100 platinum thermocouple, it is directly proportional to the change of resistance with temperature. PT100 resistance and temperature variation relationship is: when PT100 temperature 0 ℃ its resistance of 100 ohms, at 100 ℃ its resistance value is about 138. 5 ohms. Its industrial principle: when the PT100 at 0 degrees Celsius when his resistance of 100 ohms, its resistance into uniform growth as temperatures rise. Thermocouple is converted to the temperature change resistance change of an element, usually need to resistance signal through wire transfer to the computer control device or other instrument on at a time. Industrial thermocouple installed in production field, and there is a certain distance between control room, so the thermocouple wire to the measurement result will have great influence. National standard of the thermocouple wire two wire: there are three main ways in the thermocouple at both ends of the connection to elicit resistance signal way is called a wire two wire: this kind of wire method is very simple, there must be lead resistance r, but because of the connection wire r size and material of the wire and the length of the factors, so this method is only applicable to lead at a lower measuring accuracy three-wire system: at one end of the thermocouple roots connect a wire, the other end connected to the two lead way called three wire system, this way, which is equipped with a bridge can be better to eliminate the influence of the lead resistance, the lead resistance is a very commonly used in industrial process control. Four wire: on both ends of the thermocouple root way each connecting two wire called a four wire system, including two thermocouples provide constant current I, lead to voltage signal into R U, again through the other two root lead to guide U to secondary instrument. Is this way of lead can completely eliminate the resistance of the lead, it is mainly used for high precision temperature detection. Thermocouple used three wire connection. Using three wire system is to eliminate the measuring error caused by the connection wire resistance. This is because the measuring circuit of thermocouple is usually unbalanced bridge. Thermocouple as a bridge bridge arm resistance, its connection wire ( From the thermocouple is controlled by the) This part also become a part of the bridge arm resistance, resistance is unknown and change with environment temperature, cause measurement error. Using three wire system, will lead a received the power supply end of the bridge, the remaining two received thermocouple respectively the bridge arm and the adjacent bridge arm, this eliminates the wire line resistance measurement error. Industry generally adopted three wire connection.