4-8 Range, Units, Digits, Rate, and Filters Model 6485 Picoammeter Instruction Manual
Median filter control
The MEDN key is a toggle key: it will either enable the median filter (displays MEDIAN
ON) or disable the median filter (displays MEDIAN OFF). To configure the median filter:
1. Press the CONFIG key.
2. Press the MEDN key. The present rank will be displayed (flashing).
3. Use the RANGE ( or ) keys to display the desired rank (1 to 5).
4. Press ENTER to set. To return to the previously set value, press EXIT instead of
ENTER.
Digital filter
Digital filter classifications
Model 6485 has two classifications of the digital filter: averaging and advanced. Both are a
simple average of one to 100 reading conversions. The difference between them is the
user-programmable noise "window" for the advanced filter.
The noise window, which is expressed as a percentage of range (0-105%), allows a faster
response time to large signal step changes. A reading conversion outside the plus or minus
noise window fills the filter "stack" immediately.
If the noise does not exceed the selected percentage of range, the reading is based on an
average of reading conversions. In this case, the advanced filter works the same as the
averaging filter. If the noise does exceed the selected percentage, the reading is a single
reading conversion, and new averaging starts from this point. The two filter classes are
compared in Figure 4-2.
Digital filter types
An additional filter parameter is type (type is either moving or repeating). Filter types are
compared in Figure 4-3.
Moving Filter — Every time a reading conversion occurs, the readings in the stack are
averaged to yield a single filtered reading. The stack type is first-in, first-out. After the
stack fills, the newest reading conversion replaces the oldest. Note that the instrument does
not wait for the stack to fill before releasing readings.
Repeating Filter — Takes a selected number of reading conversions, averages them, and
yields a reading. It then flushes its stack and starts over.
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