Carlo Gavazzi WM5-96 - Manual (Page 37)

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WM5-96 Instruction Manual
Programming WM5 96
Example 3.
It’s necessary to stabilize the value of the displayed variable AL 1
(phase current 1), fluctuating within 470V and 486V.
To be able to manage the alarm function and following activation and
deactivation of the relay, this value is not to be subject to continuous
fluctuations. In this example we have considered using a 500/5A CT.
The paramters of the digital filter is to be programmed as follows:
RANGE: the variable has fluctuations within the mean value whose
amplitude is equal to ±1,60% of the full scale rated value of this vari-
able (obtained by means of the calculation: (486-470)/ 2= ±8A, then
±8*100/500V= ±1,60% where 500A is the value referred to the primary
of the transformer being used). The “range” parameter, which repre-
sents the action range of the digital filter, is to be programmed to a
value slightly higher than the pourcentage amplitude of the fluctuation:
for example 2.0%.
COEFFICIENT: if the new value acquired by the instrument is within
the filtering action range, the new displayed value is calculated alge-
brically adding to the previous value the variation divided by the filter-
ing 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.