Digital Filter - Brainchild C21 User Manual

3- 9 Digital Filter

3- 9 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
controller can be used. This is a first order filter with time constant
specified by FILT
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.
PV
Note
The Filter is available only for PV, and is performed for the displayed The Filter is available only for PV, and is performed for the displayed
value only. The controller is designed to use unfiltered signal for 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 even if Filter is applied. A lagged ( filtered ) signal, if used for
control, may produce an unstable process. control, may produce an unstable process.
parameter . The default value of FILT is 0.5 sec.
1 sec 1 sec
FILT=30
Figure 3.8 Figure 3.8
Filter Characteristics Filter Characteristics
FILT=0
FILT=1
1 sec 1 sec
UM0C911A
Time
44