Keithley 2700, User Manual, Page: 116 / 500

Model 2700 Multimeter/Switch System User’s Manual Basic DMM Operation 3-25
Performing offset-compensated ohms measurements
Offset-compensated ohms can only be performed on the
Ω
4 function using the 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 100
Ω
, 1k
Ω
, or 10k
Ω
range, or press
AUTO to enable auto range. If using auto range, offset compensated ohms mea-
surements 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,” page 3-23 ,
procedure.
NOTE
The OCOMP annunciator will flash when the instrument is on an invalid range
(100k
Ω
through 100M
Ω
ranges) for offset-compensated ohms. Normal ohms
measurements will instead be performed.
For buffer recall, there is no way to distinguish between a normal ohms reading
and an offset-compensated ohms reading. The OCOMP annunciator (off, on, or
flashing) has no significance for recalled resistance readings that are displayed.
Buffer operation is covered in Section 6.
With offset-compensated ohms enabled, it will be “remembered” by the
Ω
4 func-
tion after you change measurement functions (i.e., DCV). When
Ω
4 is again
selected, offset-compensated ohms will be enabled.
Measurement methods
The Model 2700 uses two methods to measure resistance:
• Constant-current source method (100
Ω
through 1M
Ω
ranges) – Sources a
constant-current to the DUT. Voltage is measured by the Model 2700 and
resistance is then calculated (R = V/I).
• Ratiometric method (10M
Ω
and 100M
Ω
ranges) – Test current is generated by a
0.7µA source in parallel with a 10M
Ω
reference resistor.