Filter Characteristics; Figure 4-2: Moving Average Filter - Keithley 3700 series Reference Manual

Series 3700 System Switch/Multimeter Reference Manual

Filter characteristics

In general, the digital filter places a specified number of A/D conversions "Filter Count" into a
memory stack. These A/D conversions must occur consecutively within a selected reading
window "Filter Window." The readings in the stack are then averaged to yield a single filtered
reading. The stack can be filled in two ways for filter type: moving or repeating. Details on digital
filter characteristics are provided in the following paragraphs.
Digital filter types
There are two digital filter types: moving and repeating.
Moving average filter
The moving average filter uses a first-in first-out stack, where the newest reading conversion
replaces the oldest. An average of the stacked reading conversions yields a filtered reading.
After the specified number of reading conversions (―Filter count‖) fill the stack, the moving filter
gives a new reading for every new conversion.

Figure 4-2: Moving average filter

Repeating average filter
The repeating filter takes a specified number of conversions, averages them and yields a filtered
reading. It then flushes its stack and starts over. This setting is useful when scanning (readings
for other channels are not averaged with the present channel). The stack is then cleared and the
process starts over.
NOTE
Document Number: 3700S-901-01 Rev. A / August 2007
The moving filter cannot be used when scanning (see
scan channel is set up to use the moving filter, the filter will not turn on.
Section 4: Range, Digits, Rate, Bandwidth, and Filter
scanning (on page 7-1)). If a
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