Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 124)

124 Publication 1756-UM009C-EN-P - December 2010
Chapter 6 Temperature-measuring Analog Modules (1756-IR6I, 1756-IT6I, and 1756-IT6I2)
Digital Filter
The digital filter smooths input data noise transients on each input channel.
This value specifies the time constant for a digital first order lag filter on the
input. It is specified in units of milliseconds. A value of 0 disables the filter.
The digital filter equation is a classic first order lag equation.
Using a step input change to illustrate the filter response, you can see that
when the digital filter time constant elapses, 63.2% of the total response is
reached. Each additional time constant achieves 63.2% of the
remaining response.
To see how to set the digital filter, see page 210 .
IMPORTANT
The digital filter is available only in applications using floating
point mode.
Yn = Yn-1 + (X
n
– Y
n
-1)
[
Δ
t]
Δ
t + TA
Yn = present output, filtered peak voltage (PV)
Yn-1 = previous output, filtered PV
Δ
t = module channel update time (seconds)
TA = digital filter time constant (seconds)
Xn = present input, unfiltered PV
0 0.01 0.5 0.99 Time in Seconds
16723
100%
63%
0
Amplitude
Unfiltered in-
TA = 0.01 s
TA = 0.5 s
TA = 0.99 s