Why is thermal resistance temperature measurement often adopted three wire connection method?
Demand leads to three wires of the cross-sectional area and length were the same, circuit for measuring platinum resistance is generally not balanced, the platinum resistance as a bridge arm resistance bridge, a bridge will lead to a power supply terminal, the other two are respectively connected to the bridge arm where the platinum resistance and its adjacent bridge arm. When the balance of the bridge, the calculation result shows that Rt=R1R3/R2+R1r/R2-r, when R1=R2, the change of wire resistance has no effect on the measurement results, so as to eliminate the measurement error caused by wire line resistance, but must be congruent arm bridge, otherwise it is impossible to completely eliminate the effect of lead resistance, but the analysis showed that the use of three wire will greatly reduce the additional error caused by resistance wire, the industry generally use three wire method. And the specific wiring reference map
Change of resistance sensor value and the connecting wire resistance value constitute the sensor output value, because of the additional error caused by the wire resistance measured for high measurement accuracy, less demanding situations, and the length of the wire should not be too long.
When the measured resistance value is very small, the resistance test line may introduce significant errors, four line measurement provides a constant current for two additional test line, the other two voltage test line measurement of the unknown resistance drop, the voltmeter input impedance is high enough under the condition of current flowing through almost no voltage meter, so that you can drop accurate measurement of the unknown resistance, obtained by calculating the resistance value.
