Contact check
The Models 2604B, 2614B, and 2634B do not perform contact check measurements.
When a contact check measurement is made, two small current sources switch between the HI and
SENSE HI terminals and the LO and SENSE LO terminals. By controlling the switches illustrated in
the following figure, the current from these sources flows through the test leads and through the
contact resistance, as shown. To accurately measure the resulting contact resistance, the differential
amplifier outputs are measured once with the current sources connected, and again with the current
sources disconnected. This allows for compensation of various offset voltages that can occur.
Figure 7: Contact check circuit
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