Keithley 2601B Reference Manual page 248

Section 4: Theory of operation
1 Voltage source (000.000 mV)
2 Ammeter
3 Positive current; current flowing out of HI results in positive measurements
4 DUT (current source)
Contact check
The Models 2604B, 2614B, and 2634B do not perform contact check measurements.
When a contact check measurement is being performed, two small current sources are switched in
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.
4-22
Series 2600B System SourceMeter® Instrument Reference Manual
Figure 106: Contact check circuit
2600BS-901-01 Rev. B / May 2013