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Every time an autorange occurs, a search for every available range of the selected function is
performed. The time it takes to perform the search could slow down range change speed signif-
icantly. For V, I and ( measurements, upper and/or lower autorange limits can be set to reduce
search time. For Q measurements, the instrument will only autorange between the two higher
charge ranges (high range group), or between the two lower charge ranges (low range group).
NOTE
Range limits and groups are not in effect for manual ranging. Every range is accessi-
ble with manual range selection.
Autorange limits for V, I and Ω
Search time for V, I and Ω can be reduced by setting upper and/or lower autorange limits. For
example, if you know the maximum input will be around 1µA, you can set the upper current
range limit to 2µA. This eliminates the 20µA, 200µA, 2mA and 20mA ranges from the search,
therefore, increasing the range change speed. Should the input exceed 2.1µA, the "OVER-
FLOW" message will be displayed.
Perform the following steps to set upper and/or lower autorange limits.
1.
Select the V, I or Ω function.
2.
Press SHIFT and then one of the following RANGE keys:
a.
Press the RANGE
b.
Press the RANGE
3.
Use the RANGE
4.
Press ENTER.
NOTE
If you attempt to select an incompatible range limit, it will be ignored and "TOO
LARGE" or "TOO SMALL" will be displayed briefly. For example, if the lower range
limit is 20V, trying to set the upper limit to 2V will result in the "TOO SMALL" error.
Autorange groups for Q
To optimize range change speed for charge measurements, the instrument will only autorange
between two ranges. With the high range group selected, the instrument can only autorange
between the 2µC and 20µC ranges. With the low range group selected, the instrument can only
autorange between the 20nC and 200nC ranges.
If the HIGH range group is presently selected and the instrument is on the 20nC or 200nC
range (autorange disabled), pressing the AUTO range key will initially select the 2µA range and
then enable autorange. If the range group is then changed to LOW, the instrument will initially
go to the 200nC range with autorange enabled. Therefore, the instrument will always stay within
the selected range group with autorange enabled.
NOTE
With the low range group selected, the "OVERFLOW" message will be displayed
when the input signal exceeds 210nC.
Perform the following steps to select autorange group for Q:
1.
Select the Q function.
2.
Press Shift and then one of the follow RANGE keys:
a.
Press the RANGE
b.
Press the RANGE
Range, Units, Digits, Rate, and Filters
key to display the present UPPER range limit.
key to display the present LOWER range limit.
and
keys to display the desired limit.
key to select the HIGH range group (2µC and 20µC).
key to select the LOW range group (20nC and 200nC).
6-3
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