Section 3: Functions and features
Model 2657A High Power System SourceMeter® Instrument Reference Manual
3-4
2657A-901-01 Rev. B/December 2012
Figure 31: 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.
To configure the filter:
1. Press
the
CONFIG
key and then the
FILTER
key.
2. Select
TYPE
, and then select the filter type:
AVERAGE
or
MEDIAN
.
•
AVERAGE: Use this menu item to select an averaging filter, then select the averaging filter type:
MOVING
or
REPEAT
.
•
MEDIAN: Use this menu item to select a median filter. The
MOVING
filter type is the only option.
3. Select
COUNT
, and then specify the filter count (1 to 100 readings).
Conversion
#1
#1
#1
Middle
value
reading
#1
Middle
value
reading
#2
Middle
value
reading
#3
A. Type: Median, readings = 3
Conversion
#2
#1
#1
Conversion
#3
#2
#1
Summary of Contents for 2657A
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