Keithley 2750, User Manual

Page: 112 / 452

Model 2750 Multimeter/Switch System User’s Manual Basic DMM Operation 3-21
The offset-compensated ohms reading is then calculated as follows:
Offset-compensated ohms reading =
Δ
V/
Δ
I
where:
Δ
V = V2 - V1
Δ
I = I2 - I1
V1 is the voltage measurement with the current source at its normal level.
V2 is the voltage measurement using the lowest current source setting.
The above 2-point measurement process and reading calculation eliminates the resistance
contributed by the presence of V
EMF
.
Enabling/disabling offset-compensated ohms
Offset-compensated ohms is enabled by pressing SHIFT and then OCOMP. When
enabled, the OCOMP annunciator is on. Offset-compensated ohms is disabled by again
pressing SHIFT and then OCOMP.
Performing offset-compensated ohms measurements
Offset-compensated ohms can only be performed on the
Ω
4 function using the 1
Ω
, 10
Ω
,
100
Ω
, 1k
Ω
, or 10k
Ω
range. Make sure you use 4-wire connections to the DUT (see
“Connections,” page 3-8 ).
NOTE
Make sure the INPUTS switch is in the correct position. To use front panel
inputs, it must be in the “F” (out) position. For switching modules, it must be in
the “R” (in) position.
1. If a switching channel is presently closed (displayed), press OPEN to open it.
2. Select the 4-wire ohms measurement function by pressing
Ω
4, and enable offset
compensated ohms by pressing SHIFT and then OCOMP (OCOMP annunciator
turns on).
3. Use the RANGE up and down keys to select the 1
Ω
, 10
Ω
, 100
Ω
, 1k
Ω
, or 10k
Ω
range, or press AUTO to enable auto range. If using auto range, offset-compen-
sated ohms measurements will not be performed if the instrument goes to the
100k
Ω
or higher range.
4. Perform steps 4 through 8 of the “ Standard resistance measurements ” procedure.
2750-900-01.book Page 21 Wednesday, August 3, 2011 7:56 AM