Publication 1766-RM001A-EN-P - October 2008
I/O Configuration 31
Analog Input Filter and Update times
The MicroLogix 1400 analog input filter is programmable. The slower the
filter setting, the more immune the analog inputs are to electrical noise.
The more immune the analog inputs are to electrical noise, the slower the
inputs will be to update. Similarly, the faster the filter setting, the less
immune the analog inputs are to electrical noise. The less immune the
analog inputs are to electrical noise, the faster the inputs will be to
update.
Input Channel Filtering
The analog input channels incorporate on-board signal conditioning, to
distinguish AC power line noise from normal variations in 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.
Programmable Filter Characteristics
Filter Setting
Value(Hz)
Filter Bandwidth
(-3 dB Freq Hz)
Settling Time
(mSec)
Resolution (Bits)
10 10 100.00 12
50 50 20.00 12
60 60 16.67 12
250 250 4 12
TIP
• 10 Hz is the default setting
• The total update time is one ladder scan time plus the settling time.
EXAMPLE
If a 250 Hz filter is selected, the maximum update Time = ladder scan time
+ 4ms
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