
Model 2651A High Power System SourceMeter® Instrument Reference Manual
Section 4: Theory of operation
2651A-901-01 Rev. A / March 2011
4-15
Source V
When configured to source voltage (V-source) as shown in the figure below, the High Power System
SourceMeter
®
Instrument functions as a low-impedance voltage source with current limit capability,
and can measure current (I-meter) or voltage (V-meter).
Sense circuitry is used to monitor the output voltage continuously and make adjustments to the V-
source as needed. The V-meter senses the voltage at the input/output terminals (2-wire local sense)
or at the device under test (DUT) (4-wire remote sense using the sense terminals) and compares it to
the programmed voltage level. If the sensed level and the programmed value are not the same, the
V-source is adjusted accordingly. Remote sense eliminates the effect of voltage drops in the test
leads, ensuring that the exact programmed voltage appears at the DUT.
The voltage error feedback to the V-source is an analog function. The source error amplifier is used to
compensate for IR drop in the test leads.
Figure 78: Source V configuration
Sense Output
Adjust V-Source
(Feedback)
Remote
SENSE HI
IN/OUT HI
Remote
IN/OUT LO
V-source
x1
V-meter
SENSE LO
Local
Local
GUARD
+
–
I-meter
1
2
2
1
NOTES: 1.
This represents a protection circuit that is very
high impedance until the voltage across it exceeds
approximately 3 V. Above 3 V, the protection turns
on and allows current to flow through it.
2.
Approximately 13 k
Ω
.
A
V
+
-
Measure only (V or I)
The figure below shows the configurations for using the High Power System SourceMeter
®
Instrument
exclusively as a voltmeter or ammeter. As shown in the figure, the instrument is configured to
measure voltage only by setting it to source 0 A and measure voltage.