Thermocouple of three kinds of electrodes is what _ instrument

Thermocouple due to its high measuring accuracy, stable performance, is widely used in industrial temperature measurement, and is made into standard benchmark instrument. In addition, different types of thermocouple have different effects. 1, two wire: 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 accuracy of measurement. 2, 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, is commonly used in industrial process control. 3, four wire: on both ends of the thermocouple root way each connecting two wire called a four wire system, including two fuses for thermocouples provide constant current I, u r into a voltage signal into, 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 is commonly three wire connection, this is in order to eliminate the measuring error caused by the connection wire resistance. And because the use different method, lead the role of the thermocouple is also different. Thermocouple choose three wire connection. Choose three wire system is in order to eliminate measurement error caused by connecting wire resistance. This is the measurement of the thermocouple is usually unbalanced bridge circuit. Thermocouple as a bridge bridge arm resistance, the connecting wire ( From the thermocouple is controlled by the) Also become a some bridge arm resistance, some resistance is don't know this and change with environment temperature, the formation of measurement error. Choose three wire system, will lead a received the power supply end of the bridge, the other two were received the thermocouple is bridge arm and the adjacent bridge arm, so eliminating the wire line resistance caused by measurement error. Thermocouple temperature measurement principle is based on a conductor or semiconductor resistance changes with the temperature change and this feature to measure temperature and parameters related to the temperature. Thermocouple are mostly made of pure metal materials, the application is a lot of platinum and copper, now have begun to use the materials such as nickel, manganese and rhodium thermocouple. Thermocouple is usually need to get the resistance signal through wire transfer to the computer control device or other secondary instrument. From the thermocouple temperature measurement principle, the measured the change in temperature is directly measured by thermocouple resistance change, therefore, the wires of a thermocouple body such as a variety of wire resistance change will affect temperature measurement.