Page 12 - AutomationNOTEBOOK volume 41

PLC Speaking continued
of communication requests coming into the CPU. If the application is communication heavy and there’s a lot of polling of information, the CPU scan can be
adversely affected.
PLC scan time can be a
big issue with high-speed applications. Let’s say you
are controlling a high-speed sorting facility, and for packaging tracking purposes your encoders are supplying 1000 pulses per revolution for every foot of a 140- fpm conveyor.
box. In these situations, specialty modules like high-speed counters, can be used to ensure no pulses are missed. These counters are designed to work independently from the CPU scan, meaning they
have their own proces- sor dedicated to tracking the pulses coming in and noth- ing else. They then feed the count over
to the CPU when it is requested.
We are here to help
Understanding PLC control
is becoming more of a demand
as our world becomes more automated. PLC scan time is
just one of the many topics that anyone new to PLCs needs to have
PLC Speaking www.automationnotebook.com | Issue 41
a firm grasp of. To help those who would like to learn more about industrial control, we are now offering absolutely free online
PLC training.
There is no purchase
required for this training and it is available 24/7/365 so you can learn at your pace and
at your convenience. Some
of the general topics covered include:
• Logic circuits
• Basic switches
• Sinking and sourcing
• I/O fundamentals
• PLC memory addressing Also available are videos
specifically covering the AutomationDirect CLICK and Do-more PLC families.
To get started today with your unlimited access to FREE online PLC training, simply register at www.automationdirect.com/ plc-training.
That is over 2,000 pulses
per second or over 2 pulses
every milli-second. At that rate,
it wouldn’t take much for the average CPU to miss a few pulses and in turn cause a swinging diverter arm to miss or crush a
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New Product Focus
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- FREE Online PLC Training
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Break Room
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