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Thermal Resistance Of The Signal Connection
Feb 28, 2018

Thermal resistance of the signal connection

Thermal resistance is the temperature change into a resistance change in the primary components, usually need to pass the resistance signal through the lead wire to the computer control device or other primary instrument.

Thermal resistance is to change the temperature change resistance changes in the primary component, usually need to pass the resistance signal through the lead wire to the computer control device or other primary instrument. Industrial thermal resistance installed in the production site, and the control room there is a certain distance between the thermal resistance of the lead on the measurement results will have a greater impact.

Current thermal resistance of the lead there are three main ways:

    Two-wire system: the two ends of the thermal resistance of each wire to connect a resistance signal is called the two-wire system: This method is very simple lead, but there must be connected wire lead resistance r, r wire size and length and material Factor, so this method is only suitable for low precision measurement of the occasion

    Three-wire system: one end of the root of the thermal resistance to connect a lead, the other end of the way to connect two lead wire called the three-wire system, this approach is usually used with the bridge supporting, can better eliminate the impact of lead resistance, The most commonly used lead resistance in process control.

    Four-wire system: the two ends of the thermal resistance of the two ends of the way to connect two wires called the four-wire system, which leads to the thermal resistance of the two lead to provide a constant current I, the R into voltage signal U, and then through the other two leads Lead U to the secondary instrument. Can be seen that this method can completely eliminate lead wire lead resistance, mainly for high-precision temperature detection.

    Thermal resistance using three-wire connection. The three-wire system is used to eliminate the measurement error caused by the connection wire resistance. This is because the circuit measuring thermal resistance is generally unbalanced bridge. Thermal resistance as a bridge arm resistance, the connecting wire (from the thermal resistance to the central control room) has become part of the bridge arm resistance, this part of the resistance is unknown and changes with the ambient temperature, resulting in measurement error. Using three-wire system, a wire connected to the power supply side of the bridge, and the other two were connected to the thermal resistance of the bridge arm and its adjacent bridge arm, thus eliminating the wire line resistance measurement error. Industry generally use three-wire connection. The thermocouple produces a millivolt signal, which is not a problem.


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