Relative; Basic Operation - Keithley 2750 User Manual

5-2 Rel, Math, Ratio, Channel Average, dB

Relative

The rel (relative) function can be used to null offsets or subtract a baseline reading from
present and future readings. When rel is enabled, the instrument uses the present reading
as a relative value. Subsequent readings will be the difference between the actual input
value and the rel value.
You can define a rel value for each function. Once a rel value is established for a measure-
ment function, the value is the same for all ranges. For example, if 50V is set as a rel value
on the 100V range, the rel is also 50V on the 1000V, 10V, 1V, and 100mV ranges.
Therefore, when you perform a zero correction by enabling REL, the displayed offset
becomes the reference value. Subtracting the offset from the actual input zeroes the dis-
play, as follows:
Actual Input – Reference = Displayed Reading
A rel value can be as large as the highest range.
Selecting a range that cannot accommodate the rel value does not cause an overflow con-
dition, but it also does not increase the maximum allowable input for that range. For exam-
ple, on the 10V range, the Model 2750 still overflows for a 12V input.
NOTE

Basic operation

NOTE
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NOTE
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5.
The various instrument operations, including Relative, are performed on the
input signal in a sequential manner. See
page D-2, for details. It includes flowcharts showing where in the processing
sequence that the Rel operation is performed.
If using switching module inputs, make sure the front panel INPUTS switch is set
to the REAR position (in). If using the front panel inputs, the switch must be in
the FRONT position (out).
Select the desired measurement function and an appropriate range setting.
Apply the signal to be relayed to a switching channel input or to the front panel
inputs.
For the Model 7700 switching module, channels 21 and 22 are available for DCI
and ACI. Channels 1 through 20 are available for all other functions.
If using a switching module, use the
nel. If using the front panel inputs (FRONT inputs selected), it does not matter if a
switching channel is closed.
Press the REL key to set the rel value. The display will zero and the REL annunci-
ator will turn on.
Apply the signal to be measured.
Model 2750 Multimeter/Switch System User's Manual
"Signal processing sequence,"
or key to select (close) the input chan-