Model 2657A High Power System SourceMeter® Instrument Reference Manual Section 4: Theory of operation
2657A-901-01 Rev. B/December 2012 4-21
In the following figure, the instrument uses a 2-wire local sensing configuration and is set to measure
current only by setting it to source 0 V and measure current. Note that to obtain positive (+) readings,
conventional current must flow from HI to LO.
Figure 87: Model 2657A measure current only
1 Voltage source (000.000 mV)
2 Ammeter
3 Positive current; positive current flowing out of HI results in positive measurements
4 DUT (current source)
Contact check
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.
A
+
–
3
1
2
4
HI
LO
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