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Lead mode of thermal resistance

A thermal resistor is a component that converts a temperature change to a change in the resistance value, usually requiring the transmission of a resistor signal through a lead to a computer control device or another instrument. Industrial thermal resistance installed in the production site, and the control room there is a certain distance, so the thermal resistance of the lead to the measurement results will have a greater impact.

At present, there are three main ways of thermal resistance.
Second-line system: At both ends of the thermal resistance to connect a wire to elicit the resistance signal is called two-line system: This lead method is very simple, but because the connection wire must have the lead resistance r,r size and the wire material and length of the factors, so this lead mode is only suitable for low measurement accuracy of the occasion.
Three-line system: In the root of the thermal resistance to connect one end of a lead, the other end of the two-wire connection is called the three-line system, which is usually matched with the bridge to use, can better eliminate the impact of lead resistance, is the most commonly used in industrial process control.
Four wire system: at the root of the thermal resistance at each end of the connection of the two wires are called four lines, of which two leads for the thermal resistance to provide constant current I, the r into a voltage signal u, and then through another two lead to the U to two meters. This lead mode can completely eliminate the resistance of the lead, mainly for high-precision temperature detection.

The thermal resistance adopts three-wire system connection method. The three-wire system is used to eliminate the measurement error caused by the connecting conductor resistance. This is because the circuit that measures the thermal resistance is generally an unbalanced bridge. As a bridge arm resistor, the connecting conductor (from the thermal resistance to the middle control chamber) is also a part of the resistance of the bridge arm, which is unknown and the measurement error is caused by the change of the ambient temperature. Using a three-wire system, the conductor will be connected to the power supply side of the bridge, the remaining two are respectively connected to the thermal resistance of the bridge arm and its adjacent bridge arm, this eliminates the wire line resistance caused by the measurement error.