5-2
Relative, mX+b, m/X+b, and log
Model 6487 Reference Manual
Relative
Relative (Rel) nulls an offset or subtracts a baseline reading from present and future read-
ings. 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
A Rel value is the same for all measurement ranges. For example, a Rel value of 1E-6 is
1µA on the 2µA range. It is also 1µA on the 20µA range and the 200µA range. Note
changing ranges does not disable Rel.
When a Rel value is larger than the selected range, the display is formatted to accommo-
date 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 20µA range, the Model 6487 still overflows for a 21µA input.
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Rel can be used on the result of the mX+b, m/X+b, or LOG calculations. How-
ever, Rel will disable whenever a math function is enabled or disabled.
Setting and controlling relative
From the front panel, there are two ways to set the Rel value. You can use the input reading
as the Rel value or you can manually key in the Rel value.
REL key
When the REL key is used to enable Rel, the present display reading is used as the Rel
value. Perform the following steps to set a Rel value:
1.
Disable zero check by pressing ZCHK.
2.
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.
3.
Press REL. The REL annunciator turns on and subsequent readings will be the dif-
ference between the actual input and the Rel value.
4.
To disable REL, press the REL key a second time or select a different measurement
function. The REL annunciator turns off.
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When Rel is disabled, the Rel value is remembered. To reinstate the previous Rel
value, press CONFIG then press REL and finally press ENTER. If the REL is
disabled and then REL is pressed again, it will determine and set a new null
value.
With zero check enabled, the REL key controls zero correct, not relative.
