Model 6517B Electrometer Reference Manual Section 9: Filters and math
6517B-901-01 Rev. C / August 2015 9-3
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:
20 V, 1 V, 3 V
The readings are re-arranged in an ascending order as follows:
1 V, 3 V, 20 V
From the above readings, it can be plainly seen that 3 V 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 ï‚´ R) + 1
Where: R is the selected rank (1 to 5)
For example, a rank of 5 uses the last 11 readings to determine the median; (2 ï‚´ 5) + 1 = 11.
Each new reading replaces the oldest reading, and the median is then determined from the updated
sample of readings.
Because of the median filter operation, a sudden change in signal level may not immediately appear
in the readings. To ensure the signal is reported correctly, at least 2*R readings need to be taken to
make the reading consistent with the signal level when the median filter is enabled.
Figure 89: Digital filter types
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