Thermal resistance is the most commonly used temperature detector in the mid-low temperature zone. Its main features are high measurement accuracy and stable performance. Among them, platinum heat is the highest measurement accuracy, it is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.
1、The principle of thermal resistance temperature measurement
Thermistor temperature measurement is based on the fact that the resistance value of a metal conductor increases as the temperature increases. Most of the thermal resistances are made of pure metal materials, and the most widely used ones are platinum and copper.
A large number of PT100 platinum thermal resistors are used in our company. The resistance of the PT100 type resistor corresponds to 100Ω at 0°C. The standard RTD circuit is generally three-wire system in China. The three-wire system is used to eliminate the measurement error caused by the resistance of the connecting wire. This is because the circuit for measuring the thermal resistance is generally an unbalanced bridge. The thermal resistance acts as a bridge arm resistance of the bridge. The connecting wire (from the thermal resistance to the central control room) also becomes part of the bridge arm resistance. This part of the resistance is unknown and varies with the ambient temperature, causing measurement errors. The three-wire system is used to connect one wire to the power supply end of the bridge, and the other two are respectively connected to the bridge arm where the thermal resistance is located and the bridge arm adjacent thereto, thus eliminating the measurement error caused by the wire line resistance.
3、Common faults and handling
(1) It is necessary to obtain the approval of the craftsman in advance for the maintenance work that may cause the process parameters to fluctuate or the interlocking alarm device and the regulating valve.
(2) Select the material of the temperature measuring sleeve and the sealing gasket according to the process medium.
(3) During the inspection, pay attention to the phenomenon that the instrument wiring can not be short-circuited or grounded, and the shielding of the computer cable should not be grounded.
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