Keithley 2651A Reference Manual page 213

Section 4: Theory of operation
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
damage the instrument. Also, when connecting an external voltage to the I-source, set the output off
state to the high-impedance mode. See
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.
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.
4-16
Model 2651A High Power System SourceMeter® Instrument Reference Manual
Figure 79: Measure-only configurations
I-source
(0.00000 μA)
A. Measure voltage only
+
V-source
(000.000 mV)
-
* Positive current flowing out of
IN/OUTHI results in positive (+)
measurements.
B. Measure current only (uses 2-wire local sense configuration)
CAUTION
®
Instrument instrument. This current could
Compliance limit (on page 2-12) for details.
IN/OUT HI
V
V-meter
IN/OUT
LO
Positive
I-meter
current*
A
IN/OUT HI
IN/OUT
LO
+
DUT (V-Source)
-
DUT (I-Source)
2651A-901-01 Rev. A / March 2011