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4-14
Filter window — The digital filter uses a window to control filter threshold. As long as the
input signal remains within the selected window, A/D conversions continue to be placed in
the stack. If the signal changes to a value outside the window, the filter resets and starts pro-
cessing again starting with a new initial conversion value from the A/D converter.
The five window selections from the front panel are 0.01%, 0.1%, 1%, 10% of range, and
NONE (no window). For remote programming, the window can be set to any value from
0.01% to 10% or NONE.
For voltage, current, and resistance, the filter window is expressed as a percent of range.
For example, on the 10V range, a 10% window means that the filter window is ±1V. For
temperature, the filter window is expressed as a percent of the maximum temperature
reading. The maximum temperature depends on which transducer is being used. For
example, for a thermistor, the maximum reading is 150°C; a 10% window means that the
filter window is ±15°C.
Filter type — There are two digital filter types: moving and repeating. The moving aver-
age filter uses a first-in, first-out stack. When the stack becomes full, the measurement
conversions are averaged, yielding a reading. For each subsequent conversion placed in
the stack, the oldest conversion is discarded and the stack is re-averaged, yielding a new
reading. This process is depicted in
For the repeating filter, the stack is filled and the conversions are averaged to yield a read-
ing. The stack is then cleared and the process starts over
ter is used for scanning, so readings from other channels are not averaged with the present
channel.
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Model 2790 SourceMeter
The moving filter cannot be used when scanning. If a 7702 scan channel is set
up to use the moving filter, the filter will not turn on. Scanning is covered in
Section
7.
®
Switch System Reference Manual
Figure
4-2A.
(Figure
4-2B). The repeating fil-
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