Section 4: Theory of operation Model 2651A High Power System SourceMeter® Instrument Reference Manual
4-16 2651A-901-01 Rev. A / March 2011
CAUTION
V-compliance must be set to a level that is higher than the measured voltage. If it is not, excessive
current will flow into the High Power System SourceMeter
®
Instrument instrument. This current could
damage the instrument. Also, when connecting an external voltage to the I-source, set the output off
state to the high-impedance mode. See Compliance limit (on page 2-12) for details.
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 IN/OUT HI to LO.
Figure 79: Measure-only configurations
IN/OUT HI
IN/OUT
LO
B. Measure current only (uses 2-wire local sense configuration)
IN/OUT HI
IN/OUT
LO
DUT (I-Source)
Positive
current*
V-source
(000.000 mV)
V-meter
I-meter
A
V
+
-
+
-
I-source
(0.00000 μA)
DUT (V-Source)
A. Measure voltage only
* Positive current flowing out of
IN/OUTHI results in positive (+)
measurements.
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.
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