3: Functions and features Series 2600B System SourceMeter® Instrument
3-4 2600BS-901-01 Rev. C / August 2016
The moving average filter uses a first-in, first-out stack. When the stack (filter count) becomes full, the
measurement conversions are averaged, yielding a reading. For each subsequent conversion placed
into the stack, the oldest conversion is discarded. The stack is averaged again, yielding a new
reading.
The median filter is used to pass the “middle-most” reading from a group of readings that are
arranged according to size. The median filter uses a first-in, first-out stack similar to the moving
average filter. For each subsequent conversion placed into the stack, the oldest conversion is
discarded. The median is then redetermined.
Figure 51: Median filter
When a moving average filter or a median filter is first enabled, the stack is empty. The first reading
conversion is placed in the stack and is then copied to the other stack locations in order to fill it. Thus,
the first filtered reading is the same as the first reading conversion. The normal moving filter process
continues. Note that a true average or median reading is not yielded until the stack is filled with new
reading conversions (no copies in the stack). For example, in the figure for the moving average filter,
it takes ten filtered readings to fill the stack with new reading conversions. The first nine filtered
readings are calculated using copied reading conversions.
Response time
The filter parameters have speed and accuracy trade-offs for the time needed to display, store, or
output a filtered reading. These affect the number of reading conversions for speed versus accuracy
and response to input signal changes.
The filter type and count affect the overall reading speed. The moving average filter is much faster
than the repeat average filter because the instrument does not have to refill the filter stack for each
reading. Also, the number of readings averaged affects reading speed; as the number of readings
averaged increases, the reading speed decreases.
Front panel filter control
Enabling the filter
The filter is enabled by pressing the FILTER key. The FILT indicator is on while the filter is enabled.
Pressing FILTER a second time disables filter.
Configuring the filter
Filter type and count are configured from the filter configuration menu. The same filter configuration is
used for all measurement functions.
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