Keithley 6430, Instruction Manual

Page: 147 / 558

Range, Digits, Speed, and Filters 6-9
Filters
Filtering stabilizes noisy measurements caused by noisy input signals. However, the more
filtering that is used, the slower the measurement process becomes. The SourceMeter uses three
stages of filtering; repeat, median, and moving. The displayed, stored, or transmitted reading is
simply the result of the filtering processes.
You can use the Auto Filter or you can manually configure the filters. With Auto Filter
enabled, the filters are configured to provide heavy filtering on the low current ranges, and less
filtering as the current range increases.
If you disable Auto Filter and manually configure the filters, that configuration is used for
every voltage and current measurement range.
Filter stages
The SourceMeter uses a 3-stage filtering system as shown in Figure 6-2. The first stage
applies the Repeat Filter to the measurement conversions. The second stage applies the Median
Filter to the output of the first stage, and the last stage applies the Moving Filter to the output of
the second stage. When a filter stage is disabled, a reading simply passes through it.
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 dis-
ables 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.
NOTE Any range change for source or measure will also reset the filters.
A/D
Conversions
Repeat
Filter
Median
Filter
Moving
Filter*
Final
Filtered
Readings
*Normal or Advanced
Figure 6-2
3-stage filtering