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Omron Module - The advantages of PLC control
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Articles Entry:LKong Source:Network Published Time:2011-7-16
Omron Module - The advantages of PLC control
Any control system goes through four stages from conception toa working plant. A PLC system brings advantages at each stage.The first stage is design; the required plant is studied and the controlstrategies decided. With conventional systems design must be completebefore construction can start. With a PLC system all that is needed isa possibly vague idea of the size of the machine and the I/O requirements(how many inputs and outputs).
The input and output cards are cheapat this stage, so a healthy spare capacity can be built in to allow for theinevitable omissions and future developments.Next comes construction. With conventional schemes, every job isa â˜one-offâ™ with inevitable delays and costs. A PLC system is simplybolted together from standard parts. During this time the writing of thePLC program is started (or at least the detailed program specificationis written).The next stage is installation, a tedious and expensive business assensors, actuators, limit switches and operator controls are cabled. Adistributed PLC system (discussed in Chapter 5) using serial links andpre-built and tested desks can simplify installation and bring huge costbenefits. The majority of the PLC program is written at this stage.
Finally comes commissioning, and this is where the real advantagesare found. No plant ever works first time. Human nature being what itis, there will be some oversights. Changes to conventional systems aretime consuming and expensive. Provided the designer of the PLCsystem has built in spare memory capacity, spare I/O and a few sparecores in multicore cables, most changes can be made quickly and relativelycheaply. An added bonus is that all changes are recorded in the PLCâ™sprogram and commissioning modifications do not go unrecorded, as isoften the case in conventional systems.
There is an additional fifth stage, maintenance, which starts once theplant is working and is handed over to production. All plants havefaults, and most tend to spend the majority of their time in some form offailure mode. A PLC system provides a very powerful tool for assistingwith fault diagnosis. A plant is also subject to many changes during its life to speed production,to ease breakdowns or because of changes in its requirements.A PLC system can be changed so easily that modifications are simpleand the PLC program will automatically document the changes thathave been made.

 

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