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Section 5: Measurement options
Relative (REL)
The REL (relative) operation subtracts a reference value from actual readings. When REL is enabled
by the REL key, the instrument uses the present reading as a relative value. Subsequent readings
are the difference between the actual input value and the REL value. You can also enter and enable
a relative value from the CONFIG-REL display.
A REL value can be established for each measurement function. The state and value of REL for each
measurement function are saved when changing functions.
Once a REL value is established for a measurement function, the value is the same for all ranges.
For example, if 15 V is set as a REL value on the 20 V range, then REL is also 15 V on the 200 V and
2 V ranges.
A relative value can be as large as the highest allowable reading for the particular function.
Selecting a range that cannot accommodate the REL value does not cause an overflow condition, but
it also does not increase the maximum allowable input for that range. For example, on the 2 mA
range, the Model 6517B still overflows for a 2.1 mA input.
Configuring REL
Pressing CONFigure REL displays the REL value for the present measurement function. You can
change the REL value using the cursor keys and the manual RANGE keys. When ENTER is pressed,
the instrument returns to the measurement display state with that value of REL enabled. If you try to
enter an invalid REL value, a message indicating the REL limit is displayed and the REL operation is
cancelled.
Note that a bench or GPIB reset clears any stored REL values and disables REL for all functions.
Enabling REL
From the normal reading display, the REL key toggles the REL operation on and off. Each time REL
is enabled by the REL key, the present reading becomes the new REL value for that function. You
cannot REL an overflow reading. To make a new reading the REL value, REL must first be disabled
and then enabled again. Disabling REL does not clear any stored REL value.
When REL is enabled, the resulting reading is the algebraic difference between the actual input value
and the REL value:
REL'd reading = actual value - relative value
With math enabled, the REL'd reading is acted on by the math operation:
displayed reading = math operation (REL'd reading)
With REL enabled, the voltage on the input may be significantly larger than the displayed
value. For example, if a 150 V REL value is stored, an applied voltage of +175 V results in a
displayed value of only +25 V.
5-20
Model 6517B Electrometer Reference Manual
6517B-901-01 Rev. C / August 2015
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