Allen-Bradley 1420-V1, User Manual, Page: 33 / 90

Rockwell Automation Publication 1420-UM001E-EN-P - March 2016 33
Unit Configuration Chapter 3
The FILTER S parameter, which represents the action range of the digital filter, is
programmed to a value that must be slightly higher than the percentage
amplitude of the fluctuation, for example, 1.0%.
FILTER CO: if the new value that is measured by the instrument is within the
action range of the filter, the new displayed value is obtained by adding
algebraically the previous value to the variation divided by the filtering
coefficient. As a consequence, a value higher than this coefficient implies a longer
settling time and therefore better stability. You generally obtain the best result by
setting the filtering coefficient to a value equal to at least 10 times the range
parameter value.
In the following example, 1.0*10=10, the stability of the filtering coefficient can
be improved by increasing the filtering coefficient; the allowed values are
included within 1 and 255.
Example 2
This example describes how to stabilize the value of the displayed System Real
Power (W), which fluctuates 300...320 kW. In this example, the load is
connected to the instrument with a 300/5 A CT and a direct measure of the
voltage.
The parameters of the digital filter must be programmed as follows.
FILTER S: the variable fluctuates within the mean value whose amplitude is
equal to ±2.78% of the full scale rated value of this variable. This value is
obtained by the following calculation:
(320 - 300)/ 2= ±10 kW,
then ±10*100/360 kW= ±2.78%,
where 360 kW is the rated value of the System Real Power of a 1420-V2
unit input, at the CT and VT ratios and obtained with the following
formula:
VLN * VT * IN * CT * 3
Where:
VLN = rated input voltage (400V for the V1 input)
VT= primary/secondary ratio of the voltage transformer being used
IN = rated current (5 A)
CT = primary/secondary ratio of the voltage transformer being used (in
this example 400*1*5*60*3=360 kW).
The FILTER S parameter, which represents the digital filtering coefficient action
range, is programmed to a value that must be slightly higher than the percentage
of the fluctuation: for example 3.0%.