Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 123)

Programming
Chapter 3
3Ć80
Figure 3.23
Digital Filter
Amplitude
Unfiltered
PV
Filtered
PV
Sampled PV for example problem
Time
4
3
2
1
0
Time
4
3
2
1
0
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Figure 3.24
Digital Filter Equation
Y
n
= Y
nĆ1
+ 0.10 (X
n
Ć Y
n Ć1
)
TA
where
Y
n =
present output, filtered PV
Y
nĆ1
= previous output, filtered PV
0.10 = module loop update time
TA = digital filter time constant
X
n
= present input, unfiltered PV
11129