Median Filter; Digital Filter - Keithley 6485 User Manual

Model 6485 and 6487 User's Manual

Median filter

The median filter is used to determine the "middle-most" reading from a group of readings
that are arranged according to size. For example, assume the following readings:
20mA, 1mA, 3mA
The readings are rearranged in an ascending order as follows:
1mA, 3mA, 20mA
From the above readings, it is apparent that 3mA is the median (middle-most) reading.
The number of sample readings used for the median calculation is determined by the
selected rank (1 to 5) as follows:
Sample readings = (2 × R) + 1
where; R is the selected rank (1 to 5)
Note that the median filter throws out the oldest of the ranked values. It is especially use-
ful for noise characterized by unwanted spikes.

Digital filter

Digital filter types
An additional filter parameter is type (type is either moving or repeating).
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.
Range, Units, Digits, Rate, and Filters 4-5