Front Panel Operation
2-59
2.13.2 Relative (REL)
The rel (relative) operation subtracts a reference value from
actual readings. When rel is enabled by the REL key, the in-
strument uses the present reading as a relative value. Subse-
quent readings will be 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 (see configur-
ing rel).
A rel value can be established for each measurement func-
tion. The state and value of rel for each measurement func-
tion 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 15V is
set as a rel value on the 20V range, the rel is also 15V on the
200V and 2V ranges.
A relative value can be as large as the highest allowable read-
ing for the particular function.
Selecting a range that cannot accommodate the rel value
does not cause an overflow condition, but it also does not in-
crease the maximum allowable input for that range. For ex-
ample, on the 2mA range, the Model 6517A still overflows
for a 2.1mA 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
) and the RANGE
▲
and
▼
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 will be displayed and the rel operation will be
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 en-
abled 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)
WARNING
With rel enabled, the voltage on the in-
put may be significantly larger than the
displayed value. For example, if a 150V
rel value is stored, an applied voltage of
+175V will result in a displayed value of
only +25V.
Multiple display of rel
One of the “multiple displays” allows you to view the read-
ing without rel applied on the bottom line of the display and
the rel’d reading on the top line. The display is available by
repeatedly pressing either the NEXT or PREVious DIS-
PLAY key to scroll through the multiple displays of the par-
ticular function. The following is a typical message for a rel
multiple display:
+000.012 mA
001.012 (without REL)
Figure 2-46
Equivalent input impedance with zero check enabled
C
IN
C
IN
= 20pF
Input
C
IN
C
IN
= 20pF
Input
C
IN
C
IN
= 20pF
Input
10M
Ω
Volts
Z
F
= 100
Ω
(mA)
100k
Ω
|| 1000pF (
µ
A)
100M
Ω
|| 220pF (nA)
100G
Ω
|| 5pF (pA)
10M
Ω
Amps and Ohms
Z
F
10M
Ω
Coulombs
1000pF
