Rockwell Automation 1790P-T4T0 CompactBlock LDX I/O Thermocouple Modules - Manual (Page 35)

Publication 1790-UM003A-EN-P
Module Data, Status, and Channel Configuration for DeviceNet 3-5
Channel Step Response Another module characteristic determined by filter frequency is channel
step response, as shown in the following table. The step response is the
time required for the analog input signal to reach 100 percent of its
expected final value, given a full-scale step change in the input signal.
Thus, if an input signal changes faster than the channel step response, a
portion of that signal will be attenuated by the channel filter. The channel
step response is calculated by a settling time of 3 x (1 / filter frequency).
Channel Cutoff
Frequency The channel cutoff frequency (-3 dB) is the point on the input channel
frequency response curve where frequency components of the input
signal are passed with 3 dB of attenuation. The following table shows
cutoff frequencies for the supported filters.
All frequency components at or below the cutoff frequency are passed by
the digital filter with less than 3 dB of attenuation. All frequency
components above the cutoff frequency are increasingly attenuated, as
shown in the following graphs for several of the input filter frequencies.
Table 3.5 Filter Frequency vs. Channel Step Response
Filter Frequency Step Response
10 Hz 300 ms
25 Hz 120 ms
50 Hz 60 ms
60 Hz 50 ms
100 Hz 30 ms
250 Hz 12 ms
500 Hz 6 ms
Table 3.6 Filter Frequency vs. Channel Cutoff Frequency
Filter Frequency Channel Cutoff Frequency
10 Hz 2.62 Hz
25 Hz 6.55 Hz
50 Hz 13.1 Hz
60 Hz 15.7 Hz
100 Hz 26.2 Hz
250 Hz 65.5 Hz
500 Hz 131 Hz
IMPORTANT
Channel cutoff frequency should not be confused with
channel update time. The cutoff frequency simply
determines how the digital filter attenuates frequency
components of the input signal.