Filters; Filter Types; Response Time Considerations; Front Panel Filter Control - Keithley 2601 Reference Manual

Section 6: Range, Digits, Speed, Rel, and Filters

Filters

Filter lets you set the filter response to stabilize noisy measurements. The SourceMeter uses a
digital filter, which is based on reading conversions. The displayed, stored, or transmitted reading
is an average of many reading conversions (from 1 to 100).

Filter types

There are three filter types from which to choose. These three filters are broken down into two
averaging filters and one median filter. The median filter is only available on Models 2635 and
2636.
The two averaging filters are repeating and moving (Figure 6-1). For the repeating filter (which is
the power-on default), the stack (filter count) is filled, and the conversions are averaged to yield a
reading. The stack is then cleared, and the process starts over.
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 re-averaged, 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 re-determined.
When a moving filter is first enabled, the stack is empty. Keep in mind that a filtered reading is not
yielded until the stack is full. 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 Figure 6-1A, 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 considerations

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.

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 for Models 2601, 2601, 2611, and 2612
Press CONFIG and then FILTER to display the filter configuration menu:
• AVERAGE-TYPE — Use this menu item to select filter type
(MOVING or REPEAT).
• AVERAGE-COUNT — Use this menu item to specify filter count
(1 to 100 readings).
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Series 2600 System SourceMeter® Instruments Reference Manual
Return to Section Topics 2600S-901-01 Rev. C / January 2008