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4 10 Digital Filter
In certain application the process value is too unstable to be read. To improve
this a programmable low pass filter incorporated in the ZEL - 2500 can be
used. This is a first order filter with time constant specified by FILT
parameter which is contained in setup menu. The default value of FILT is 0.5
sec. before shipping. Adjust FILT to change the time constant from 0 to 60
seconds. 0 second represents no filter is applied to the input signal. The filter
is characterized by the following diagram.
Menu
FILT
Filter is used to stabilize the
process display.
PV1
FILT=0
1 sec
FILT=1
Figure 4.7
Filter Characteristics
FILT=30
1 sec
Time
Note
The Filter is available only for PV1, and is performed for the displayed value
only. The controller is designed to use unfiltered signal for control even if
Filter is applied. A lagged ( filtered ) signal, if used for control, may produce
an unstable process.
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