Keithley 2790 User Manual

Model 2790 SourceMeter
®
Switch System User’s Manual 6-3
High ohms measurements
The 7751 and 7753 include a programmable V-source (50 to 500V), so the constant volt-
age method can be used to measure high resistance (such as insulation resistance). The
Model 2790 mainframe does not have a voltage source.
If not using a 7751 or 7753 module in your test system, you can use the Ω2 function
(100MΩ range) of the Model 2790 to measure insulation resistance up to 120MΩ.
4-wire ohms
4-wire ohms eliminates the effects of test lead resistance when measuring a low ohms
DUT. Figure 6-1 shows how 2-wire ohms can be adversely affected when measuring a low
ohms DUT.
If the test lead resistance (R
LEAD
) is relatively large in comparison to the resistance of the
DUT (R
DUT
), the measured voltage (V
MEAS
) will include the voltage drops across the two
test leads. Therefore, the measured voltage (which is used to calculate resistance) will not
be the same as the actual voltage (V
R
) across RDUT.
Figure 6-1
Using ΩΩ
ΩΩ
2 function to measure resistance
I SOURCE
(1mA)
RLEAD
RMEAS =
V
MEAS
ISOUR
Keithley 2790
v
RLEAD
RDUT
VMEAS
Input HI
Input LO
VMEAS VR
VMEAS = Voltage measured by 2790 DMM
VR = Voltage across RDUT
= R
DUT + (2 x RLEAD)
R
DUT =
V
R
ISOUR
Ω2 Function Selected
Test Current

Keithley 2790 Specifications

General

Brand	Keithley
Model	2790
Category	Switch
Language	English