I-4 Applications Guide Model 6485 Picoammeter Instruction Manual
The 1mV voltage burden caused a 20% current reduction. Percent error in a measured
reading (I
M
) due to voltage burden can be calculated as follows:
The voltage burden of Model 6485 depends on the selected range (see specifications).
Voltage burden may be reduced by performing the voltage offset correction procedure.
Voltage offset correction procedure
NOTE To maintain specified operation, any time there is a substantial change in the
ambient temperature, the voltage offset procedure should be performed and
saved.
1. Press the MENU key to display the following:
CAL: VOFFSET
2. Press ENTER. The instrument will prompt as follows:
INPUT CAP
3. It is not necessary to disconnect signal cables from the 6485, but it is recommended
that signal currents be reduced to zero if possible. During the calibration, the input
impedance will be 3.5MΩ, therefore continued signal currents will present a corre-
sponding voltage to the DUT.
4. Press ENTER to complete offset voltage calibration.
5. Press EXIT to return to normal display.
NOTE Like the other calibration procedures, this calibration is not permanently stored
until CAL:UNLOCK and CAL:SAVE have been performed. Saving the results of
this calibration at a temperature other than that at which the Model 6485 will be
used will adversely affect measurement results.
I
M
% error
100%
V
S
/V
B
()
----------------------=
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