Micro resistance test, 4 wire resistance test, switching method
This method of measurement seems to be a bit of a problem because the measurement of resistance with a four wire method would have eliminated the effects of contact resistance and wire resistance.
The principle is that the T1T2 M1M2 of the outer end of N1N2 M1M2's (M1M2 to minimize the resistance of the distance between the current flow to the T2), is through the T1 M1 R M2, N1N2 is the measured voltage, internal resistance is large, so no current in N1N2M1M2, so there is not the effect of measurement resistance to the measuring system of line resistance and contact resistance.
In the test of small resistance, in order to eliminate the error caused by the lead wire resistance on the measurement, using four wire measurement; in order to eliminate the influence of contact resistance on the measurement of small electric resistance, voltage test leads L3, L4 should not be connected in M1, M2, and M1, M2 in the inside connection (that is close to the measured resistance), pressure drop contact resistance voltage L3, L4 measured not including M1, M2 on; so the test micro resistance, contact resistance does not require measurement of M1, M2.
