Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 96)

Preface MicroLogix 1000 Programmable Controllers User Manual
5–4
The total update time for each channel is a combination of the Update Time and the
Settling Time. When more than one analog input channel is enabled, the maximum
update for each channel is equal to one ladder scan time plus the channel’s Update
Time plus Settling Time. When only one analog input channel is enabled, the
maximum update for the channel is equal to the Update Time plus one ladder scan
time.
Update Examples
Example 1 – All (4) channels enabled with 60 Hz filter selected (default settings).
Maximum Update Time = (4) x ladder scan time
+ (4) x 16.67 ms
+ (4) x 66.67 ms
= 333.36 ms + (4) x ladder scan times
( Each channel will be updated approximately three times per second.)
Example 2 – 1 channel enabled with 250 Hz filter selected.
Maximum Update Time = ladder scan time + 4 ms
Input Channel Filtering
The analog input channels incorporate on-board signal conditioning. The purpose
of this conditioning is to reject the AC power line noise that can couple into an
analog input signal while passing the normal variations of the input signal.
Frequency components of the input signal at the filter frequency are rejected.
Frequency components below the filter bandwidth (–3 dB frequency) are passed
with under 3 dB of attenuation. This pass band allows the normal variation of
sensor inputs such as temperature, pressure and flow transducers to be input data to
the processor.
Noise signals coupled in at frequencies above the pass band are sharply rejected.
An area of particular concern is the 50/60 Hz region, where pick-up from power
lines can occur.