6-8 Range, Units, Digits, Rate, and Filters
Filters
Filtering stabilizes noisy measurements caused by noisy input signals. The Model 6514 uses
two types of filters: median and digital. The displayed, stored or transmitted reading is simply
the result of the filtering processes. Note that both the median and digital filters can be in effect
at the same time.
With both filters enabled, the median filter operation is performed first. After the median filter
yields a reading, it is sent to the stack of the digital filter. Therefore, a filtered reading will not
be displayed until both filter operations are completed.
The settings for the filter are global. Therefore, the filter configuration applies to all four mea-
surement functions. The MEDN key is used to configure and control the median filter, and the
AV G key is used to configure and control the digital filter. When either the median or digital filter
is enabled, the FILT annunciator is on.
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:
20V, 1V, 3V
The readings are re-arranged in an ascending order as follows:
1V, 3V, 20V
From the above readings, it is apparent that 3V 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 example,
if the median filter is configured to sample 11 readings (Rank 5), the first filtered reading will be
calculated (and displayed) after 11 readings are acquired and placed in its filter stack. Each sub-
sequent reading will then be added to the stack (oldest reading discarded) and another median
filter reading will be calculated and displayed. The median filter operation will reset (start over)
whenever the Zero Check operation is performed or the function is changed.
Median filter configuration control
The MEDN key is a toggle-action key. It will either disable the median filter (displays
“MEDIAN OFF”), or access the configuration menu to enable the median filter.
1. Press the MEDN key to display the present filter rank.
2. Use the RANGE
or key to display the desired rank (1 to 5) and press ENTER.
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