Spectrum Controls 1746sc-INI4vi - Manual (Page 25)

Chapter 3: Things To Consider Before Using Your Module 21
Important – A data word is valid only when the channel is enabled and
there are no channel errors. A status word is valid only when the channel
is enabled and the module has processed all configuration changes.
The Difference Between
Channel Update Time &
Step Response Time
The speed of an analog module can be defined in 2 distinctly different
ways: either by the channel update time or by the full-scale step response
time.
• The channel update time is the time required for your module to
sample and convert the input signal of an enabled channel and make
the resulting data available to the processor.
• The full-scale step response time is the time required for a channel’s
data word to reach 95% of the expected, final value, given a full-scale
step change in the input signal. This means that if an input signal
changes faster than the full-scale step response time, the signal value
provided to the processor has not reached 95%.
Figure 5 illustrates the difference between channel update time and full-
scale step response time:
Figure 5. Channel update time and full-scale step response time
100
80
60
40
20
0
Channel Updates
Percent (%) of final value
Full-Scale Step Response Time
Time (ms)
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.