Rockwell Automation 1420 PowerMonitor 500 User Manual

Page 31

Rockwell Automation Publication 1420-UM001D-EN-P - September 2013

Unit Configuration

Chapter 3

FILTER CO: if the new value 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 a 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 between 300 kW and 320 kW. In this example, the

load is connected to the instrument by means of 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 an 1420-V2 unit input, at the above mentioned CT and VT ratios

and obtained by means of 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 RANGE parameter, representing the digital filtering coefficient action

range, is to be programmed to a value that must be slightly higher than the

percentage of the fluctuation: for example 3.0%.