A
PLC (i.e. Programmable Logic Controller) is a device that was invented
to replace the necessary sequential relay circuits for machine control.
The PLC works by looking at its inputs and depending upon their state,
turning on/off its outputs. The user enters a program, usually via software,
that gives the desired results.
PLCs
are used in many "real world" applications. If there is industry
present, chances are good that there is a plc present. If you are involved
in machining, packaging, material handling, automated assembly or countless
other industries you are probably already using them. If you are not,
you are wasting money and time. Almost any application that needs some
type of electrical control has a need for a plc.
For
example, let's assume that when a switch turns on we want to turn a
solenoid on for 5 seconds and then turn it off regardless of how long
the switch is on for. We can do this with a simple external timer. But
what if the process included 10 switches and solenoids? We would need
10 external timers. What if the process also needed to count how many
times the switches individually turned on? We need a lot of external
counters.
As
you can see the bigger the process the more of a need we have for a
PLC. We can simply program the PLC to count its inputs and turn the
solenoids on for the specified time.
This
site gives you enough information to be able to write programs far more
complicated than the simple one above. We will take a look at what is
considered to be the "top 20" plc instructions. It can be
safely estimated that with a firm understanding of these instructions
one can solve more than 80% of the applications in existence.
That's right, more than 80%! Of course we'll learn more than just these instructions to help you solve almost ALL your potential plc applications.
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