6-8 Range, Digits, Speed, and Filters Models 2500 and 2502 User’s Manual
Each filter stage uses a stack to temporarily store readings to be filtered. The size of a
stack, which is set by the user, determines how many readings will be filtered. A stack size
of one disables that filter.
NOTE A source level change due to a sweep step resets the filters. That is, readings are
flushed from stack, and the filtering process starts over at the beginning. When
not sweeping, source level changes do not reset the filters.
Any range change will also reset the filters.
Repeat filter
The Repeat Filter places the specified number of measurement conversions into a stack
and averages them to yield a single Repeat Filter reading. The stack is then cleared, and
the process starts over. For example, if the repeat count (stack size) is 10, every 10 mea-
surement conversions will yield a single reading. Figure 6-3 illustrates the Repeat Filter
process. The maximum count (stack size) for the Repeat Filter is 100. Note that setting the
count to one disables the Repeat Filter.
Choose the Repeat Filter for sweeping so readings for other source levels are not averaged
with the present source level.
Figure 6-3
Repeat filter (count 10)
Median filter
The Median Filter is used to pass the middle-most reading from a group of readings that
are arranged according to size. For example, assume the following readings:
2mA, 1nA, 3nA
The readings are placed in a stack, rearranged in ascending order as follows:
1nA, 3nA, 2mA
From the above readings, it can be plainly seen that 3nA is the median (middle-most)
reading. Therefore, the 3nA reading is allowed to pass, while the other two readings are
discarded (filtered out). The Median Filter provides a good method to reject noise spikes.
Conversion #10
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Conversion #1
Repeat
Reading
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Conversion #20
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#16
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Conversion #11
Repeat
Reading
#2
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Conversion #30
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Conversion #21
Repeat
Reading
#3
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