Rockwell Automation 1420 PowerMonitor 500 - Manual (Page 32)

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Rockwell Automation Publication 1420-UM001D-EN-P - September 2013
Chapter 3
Unit Configuration
FILTER CO: if the new value acquired by the unit is within the filtering action
range, 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 higher settling time and therefore
better stability. Generally speaking, the best result is obtained by setting the
filtering coefficient to a value equal to at least 10 times the value of the range
parameters. In the example, 3.0*10=30. To improve the stability, you can increase
the filtering coefficient; the admitted values are included within
1 and 255.
Example 3
It is necessary to stabilize the value of the displayed variable AL 1
(phase current 1), which fluctuates in the range 470 A and 486 A.
To be able to manage the alarm function and activation and deactivation of the
relay, this value is not to be subject to continuous fluctuations. In this example,
we have considered using a 500/5 A CT. The parameters of the digital filter are to
be programmed as follows.
FILTER S: the variable fluctuates within the mean value whose amplitude is
equal to ±1.60% of the full scale rated value of this variable (obtained by means of
the calculation: (486-470)/ 2= ±8 A, then ±8*100/500 A= ±1.60%
where 500 A is the value referred to the primary of the transformer being used).
The ‘range’ parameter, which represents the action range of the digital filter, is to
be programmed to a value slightly higher than the percentage amplitude of the
fluctuation, for example 2.0%.
FILTER CO: if the new value acquired by the instrument is within the filtering
action range, the new displayed value is calculated algebraically adding to the
previous value the variation divided by the filtering coefficient. As a consequence,
a higher value of this coefficient implies a higher settling time and therefore a
better stability. Generally speaking, the best result is obtained setting the filtering
coefficient at a value equal to at least 10 times the value of the range parameter. In
the example, 2.0*10=20. To improve the stability you can increase the filtering
coefficient; the admitted values are within 1 and 255.