User manual

2-10 Connections 2400 Series SourceMeter
®
User’s Manual
Figure 2-5 shows how to make connections to measure the resistance of a single
resistor (DUT) in a resistor network. See Section 6, “Guard,” for more information
on guarded ohms measurements.
The basic connection scheme for guarded ohms measurements is shown in Fig-
ure 2-5A. If the guard resistance path (R
G)
is <1kΩ, IR drop in the GUARD test
lead could be high enough that the guard voltage at the resistor network is signifi-
cantly 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 resistor network as shown in Figure 2-5B.
Guard sense ensures that the guard voltage at the 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 (Figure 2-5C).
NOTE Guard current (I
G
) must never exceed 50mA. If it does, guard voltage will
become less than the output voltage and corrupt the measurement.