Allen-Bradley 1420-V1, User Manual, Page: 32 / 90

32 Rockwell Automation Publication 1420-UM001E-EN-P - March 2016
Chapter 3 Unit Configuration
Digital Filtering Operation Digital filtering smooths out the display of fluctuating values. The parameter
FILTER S defines the operating range of the filter. This operating range is
represented as a yellow band (each small square is one digit). While the measured
value (red curve in
Figure 23 ) is within this band, the filter is active. Once the
value exceeds the operating range, the filter is deactivated and a new band is active
around the new value. The range of fluctuation (in digits) is a good starting value
for such parameters.
The parameter FILTER CO represents the filtering coefficient. The higher the
FILTER CO, the smoother the curve of the displayed values (black in
Figure 23 ).
There is not a theoretical rule to define this parameter, it is set in the field. One
rule is to start with the value of the FILTER S coefficient and then increase
FILTER CO until the desired stability is reached.
The digital filter affects the values retransmitted both via serial communication
and analog output.
Figure 23 - Digital Filter
Digital Filter Programming Examples
This section gives digital filter programming examples.
Example 1
This example describes how to stabilize the displayed value of the VL-N variable,
which fluctuates between 222V and 228V. The parameters of the digital filter
have to be programmed as follows.
FILTER S: The variable fluctuates within the mean value whose amplitude is
equal to ±0.75% of the full scale rated value of the variable itself, which is
obtained by the following calculation:
(228 - 222)/ 2= ±3V, then ±3*100/400V= ±0.75%
where 400V is the line-to-neutral rated value of a 1420-V2 unit input
No filter action
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