Features Of A Plc; Cycle - IFM Electronic ecomot mobile R 360 Serie Starterset-Handbuch

1.5.

Features of a PLC

Cycle

The advantages of a PLC as compared to a conventional contactor controller
does no longer need to be pointed out today. Now there are also controllers
with mechanical and electrical features which are necessary for use in mobile
machines, e.g. protection IP 67, high mechanical stability and electrical noise
immunity. These may also be the reasons why the reader has decided to use
the ecomat mobile system. For those who do not yet have any experience with
a PLC some features which sometimes present problems will be briefly
described in this chapter.
Cyclical One characteristic of PLC systems is the cyclical program processing. This has
program some consequences for programming which will be briefly shown below.
processing
Figure2: Cyclical Program Processing
An example is to explain why this type of programming makes sense. Let us
assume that the following instructions are in the program:
If the selector switch is on 0 (logical FALSE), then switch the output "move
to the left".
If the selector switch is on 1 (logical TRUE), switch the output "move to the
right".
At first glance everything seems to be clear. The switch can either be on 0 or 1.
However, it has to be noted that such a program is processed in sequence, e.g.
instruction after instruction. Nevertheless, sometime the following event may
come up (this is where Murphy's law applies):
The selector switch is on 0, therefore the output "move to the left" is
switched.
R
What you should know
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