Model 6487 Reference Manual Range, Units, Digits, Rate, and Filters 4-9
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)
For example, a rank of 5 will use the last 11 readings to determine the median;
(2 × 5) + 1 = 11. Each new reading replaces the oldest reading and the median is then
determined from the updated sample of readings.
Median filter operation — The median filter operates as a moving type filter. For exam-
ple, if the median filter is configured to sample 11 readings (Rank 5), the first filtered read-
ing will be calculated (and displayed) after 11 readings are acquired and placed in its filter
stack. Each subsequent reading will then be added to the stack (oldest reading discarded)
and another median filter reading will be calculated and displayed. The median filter oper-
ation will reset (start over) whenever the Zero Check operation is performed or the range
is changed.
Median filter control
To configure the median filter:
1. Press the CONFIG key.
2. Press the FILT key.
3. Select MEDIAN, then press ENTER.
4. Change the display to MEDIAN ON, then press ENTER.
5. The present rank will be displayed (flashing).
6. Use the RANGE ( or ) keys to display the desired rank (1 to 5).
7. Press ENTER to set. To return to the previously set value, press EXIT instead of
ENTER.
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