6-10
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2600AS-901-01 Rev. B / September 2008
Section 6: Range, Digits, Speed, Rel, and Filters
Series 2600A System SourceMeter® Instruments Reference Manual
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 re-determined.
When a moving 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 stack). For example, in
, it takes ten filtered readings to fill
the stack with new reading conversions. The first nine filtered readings are calculated using copied
reading conversions.
Front panel filter control
Configuring filter
Filter type and count is configured from the filter configuration menu. The configured filter is the
same for all measurement functions.
Filter configuration menu
Press
CONFIG
and then
FILTER
to display the filter configuration menu:
•
TYPE:
Use this menu item to select filter type:
–
AVERAGE:
Use this menu item to select an averaging filter, then select the averaging
filter type:
•
Moving
•
Repeat
–
MEDIAN:
Use this menu item to select a median filter. The MOVING WINDOW filter type
is the only option.
•
COUNT:
Use this menu item to specify filter count (1 to 100 readings).
Enabling 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.
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 averaging mode and count affect the overall reading speed. The moving averaging filter
is much faster than the repeat averaging filter because the unit does not have to refill the filter
stack for each reading. Also, the number of readings averaged will affect reading speed; as the
number of readings averaged increases, the reading speed decreases.
