As long as zero-adjustment is performed by properly shorting the four test leads, it is possible not only to eliminate the effects of contact resistance, but also to ignore the effects of wiring resistance values r1 to r4. In four-terminal measurement, the circuit that applies the constant current and the circuit that includes the voltmeter are independent up to both ends of the measurement target. In addition, it is not able to yield an accurate reading if the resistance R0 is small. However, this method is not able to eliminate the effects of the contact resistance between the test leads and the measurement target. To reduce the impact of the wiring resistance on measured values, it is necessary to perform zero-adjustment by shorting the test leads before measuring the resistance R0. ![]() They use a voltmeter to detect the resistance value of resistance R0 while applying a constant current to the measurement target, and the resulting reading includes the wiring resistance r1 and r2. ![]() Most digital testers measure resistance with two terminals.
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