Spectrum Controls 1746sc-INI4i, User Manual

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Chapter 3: Configuring the 1746sc-INI4I 3-3
User’s Manual Pub. 0300266-04 Rev. A
Figure 3-2.. Channel Update Time and Full-scale Step Response Time
The actual channel update time and full-scale step response time depend on a
number of things, such as the filter frequency selected. Because of this, the
number of channel updates than can occur before the channel data word reaches
95% of its expected value can vary.
In general, you can reduce the channel update time by doing any of the following:
•
Disabling unused channels
• Selecting a higher frequency input filter
You can reduce the full-scale step response time by:
•
selecting a higher frequency input filter
NOTE
Selecting a higher frequency input filter decreases the noise rejection and
effective resolution, as described below.
For the fastest possible channel update time, enable only one channel and
select a 250 or 500 Hz filter. Conversely, your module operates most
slowly if you enable all 4 channels and select a 50 Hz filter for each.
Section 3.3
Selecting An Input Filter
Frequency
The 1746sc-INI4i and 1746sc-INI4vi input modules use a digital filter to reject
the high-frequency noise that can couple into an analog input signal. This digital
filter is programmable, letting you select one of four filter frequencies for each
channel. The digital filter provides the highest noise rejection at the selected filter
frequency. For example, to reject the noise associated with 60 Hz power, you
may want to select the 60 Hz filter.
The filter frequency you select determines that channel’s 3 dB cut-off frequency,
full-scale step response time, worst-case effective resolution, and channel update