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Model 6517B Electrometer Reference Manual
Ohms ranges
Each measurement range for the ohms function has a lower reading limit that is one decade below
the selected range. For example, the 20 MΩ range has a lower reading limit of 2 MΩ. The reading
ranges for the ohms function are listed in the following table.
Ohms measurements are performed by sourcing voltage and measuring current. Thus, ohms ranges
are actually current ranges with ohms displayed.
When the resistance of the DUT (device under test) is too low for the selected ohms range, the
resultant current exceeds full scale and cause the UNDERFLOW message to be displayed. This
message indicates that the measured resistance is below the lower reading limit of the selected
range.
This problem can be resolved by manually selecting the next lower range or by using AUTO range.
There are three ways you can be assured of optimum range selection:
Use AUTO range.
Select the next lower range when UNDERFLOW is displayed.
With the MANUAL V-source selected, use the multiple (NEXT) display that provides the actual
measured current. This allows you to check that the selected amps range is the lowest range that
can handle the measured current.
Note that with AUTO range selected, the instrument cannot go to the 2 TΩ, 20 TΩ, or 200 TΩ ranges
since a hazardous voltage level (400 V) may be selected by the instrument. You must select these
ranges manually. To speed up the auto range process, you can set upper and lower range limits.
Eliminating ranges in the auto range search speeds up the measurement process.
With AUTO V-source selected, the Model 6517B displays the ohms measurement range and the V-
source value. With MANUAL V-source selected, the amps range for the measurement and the V-
source value is displayed.
Since AUTO ohms uses the source V, Measure I measurement method, a current measurement
overflow results in an UNDERFLOW error. Conversely, a 0 A measured current results in an
OVERFLOW error. To avoid confusion, use NEXT to show the measured current on the secondary
display.
Ohms reading ranges and AUTO V-source
Reading range
200 kΩ – 2 MΩ
2 MΩ – 20 MΩ
20 MΩ – 200 MΩ
200 MΩ – 2 GΩ
2 GΩ – 20 GΩ
20 GΩ – 200 GΩ
200 GΩ – 2 TΩ
2 TΩ – 20 TΩ
20TΩ – 200TΩ
6517B-901-01 Rev. C / August 2015
AUTO V-source
Test voltage
Amps range
40 V
200 µA
40 V
20 µA
40 V
2 µA
40 V
200 nA
40 V
20 nA
40 V
2 nA
400 V
2 nA
400 V
200 pA
400 V
20 pA
Section 4: Basic measurements
4-19
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