Ohms Guard - Keithley SourceMeter 2400 User Manual

®
2400 Series SourceMeter User's Manual

Ohms guard

Use the guarded ohms connection schemes shown in
measure operation:
• In-circuit resistance measurements on the DUT where other parasitic leakage
devices are present.
Note that ohms guard must be selected for this connection scheme. Ohms guard is not
available for the 1A range (source or measure). See
ohms guard and Section
Figure 2-5 shows how to make connections to measure the resistance of a single resistor
(DUT) in a resistor network. See
ohms measurements.
The basic connection scheme for guarded ohms measurements is shown in
the guard resistance path (R
enough that the guard voltage at the resistor network is significantly less than the output
voltage at the DUT. This results in leakage current and will corrupt the measurement. To
cancel the effect of IR drop in the GUARD test lead, connect GUARD SENSE to the resis-
tor network as shown in
resistor network is the same as the output voltage at the DUT.
Note that if the DUT is <1kΩ, you should use the 4-wire measurement method (remote
sensing) by connecting SENSE HI and LO to the DUT and enabling remote sense
2-5C).
NOTE
Guard current (I
become less than the output voltage and corrupt the measurement.
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Figure 2-5
"Guard selection," page
4, "6-wire ohms measurements."
Section 6, "Guard," for more information on guarded
is <1kΩ, IR drop in the GUARD test lead could be high
G)
Figure 2-5B. Guard sense ensures that the guard voltage at the
) must never exceed 50mA. If it does, guard voltage will
G
Connections 2-9
for the following source-
2-12, to select
Figure 2-5A. If
(Figure