Keithley 2182, User Manual, Page: 85 / 339

Relative, mX+b, and Percent (%) 4-3
Relative
Relative (rel) nulls an offset or subtracts a baseline reading from present and future readings.
When a rel value is established, subsequent readings will be the difference between the actual
input and the rel value.
Displayed (Rel’ed) Reading = Actual Input - Rel Value
Once a rel value is established for a measurement function, the value is the same for all
ranges. For example, if 5V is set as the rel value on the 10V range for DCV1, the rel value is also
5V on the 100V, 1V, 100mV, and 10mV ranges.
When a rel value is larger than the selected range, the display is formatted to accommodate
the rel’ed reading. However, this does not increase the maximum allowable input for that range.
An over-range input signal will still cause the display to overflow. For example, on the 10V
range, the Model 2182 still overflows for a 12V input.
NOTE Rel’ed readings are used for Ratio and Delta calculations. See Section 5 for more
information on using Relative with Ratio and Delta.
For offsets that vary, the DC current-reversal technique should be used instead of REL. This
technique uses the Delta measurement mode of the Model 2182 to cancel offsets. See “ Delta ”
in Section 5 for details.
REL Key
The REL key sets a rel value for the selected function (DCV1, DCV1, TEMP1, and TEMP2).
Note that a unique rel value can be established for each measurement function.
Perform the following steps to set a rel value:
1. Display the reading you want as the rel value. This could be a zero offset reading that
you want to null out, or it could be an applied level that you want to use as a baseline.
2. Press REL. The REL annunciator turns on and subsequent readings will be the difference
between the actual input and the rel value.
3. To disable REL, press the REL key a second time. The REL annunciator turns off.
NOTE You can manually set a rel value using the mX+b function. Set M for 1 and B for the
desired rel value. See “
mX+b ” for more information.
Analog Output Rel — A rel value can also be established for analog output. When Analog
Output Rel is turned ON, the present analog output voltage is used as the rel value. Subsequent
analog output readings will be the difference between the actual analog output and the rel value.
To enable Analog Output Rel, press SHIFT and then OUTPUT. The message “AOUT REL
ON” will be displayed briefly to indicate that it is enabled. To disable Analog Output REL, press
SHIFT and then OUTPUT a second time. The message “AOUT REL OFF” will be displayed
briefly.
See Section 10 ( Analog Output ) for more information on Analog Output.