Section 4: Theory of operation Model 2657A High Power System SourceMeter® Instrument Reference Manual
4-18 2657A-901-01 Rev. B/December 2012
Basic circuit configurations
Source V
When configured to source voltage (V-source), as shown in the figure below, the instrument functions
as a low-impedance voltage source with current limit capability, and can measure current (I-meter) or
voltage (V-meter).
Sense circuitry continuously monitors the output voltage and makes adjustments to the V-source as
needed. The V-meter senses the voltage at the HI and LO 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
source voltage 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.
With 4-wire sensing enabled, both remote sense leads must be connected or incorrect operation will
occur. Use contact check to verify that the sense leads are connected (see Contact check
measurements (on page 2-37)). To limit the maximum output voltage between HI and LO in case of
poor sense lead connection, use Overvoltage protection (OVP)
(on page 2-65).
Figure 84: Source V configuration
Feedback
Remote
SENSE HI
HI
Remote
LO
V-source
x1
V-meter
SENSE LO
Local
Local
GUARD
+
–
I-meter
1
2
2
1
A
V
+
-
NOTES: 1. This represents a protection circuit. Do not apply more than 3030 V
between HI and SENSE HI. To maintain optimal operation and obtain
accurate measurements, the maximum voltage between HI and SENSE HI
should be no more than 3 V. This limit also applies to the maximum voltage
between LO and SENSE LO.
2. Approximately 80 kΩ.
2
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