Selection Criteria of PLC When Installing WHR

  • Thread starter Kingrosekhan123
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Thread Starter


i want to know the general rule for the selection of PLC. we are going to install waster heat recovery of 12MW.

how i can select CPU and Brand of PLC?

any equation regarding input output, AI/AO for estimating memory, etc.?

please guide me in good way. i have experience of 1 year.

my E.mail Address is
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You need detailed knowledge of the process and what control functions it requires:

- pumps
- valves
- temperature probes
- operator controls

A Process and Instrumentation Drawing is useful.

Then work out what I/O you require.

There used to be formulas for CPU type and memory but you rely an educated guess -100k minimum for medium sized applications.

Any SCADA or advanced operator controls ?

PLC brand is an open choice, generally the end user/client has an idea.

Bob Peterson

Pretty much any brand will have the capability to do a run of the mill task like this.

It most often comes down to someone (end user, OEM, or integrator) deciding what PLC brand to use based on their own criteria, often whatever they are most familiar with, or is otherwise most cost effective for them to use.

My inclination would be to use whatever you already have in the plant so that spares and training is less of an issue.


if we talk in general manners then what are the general rules for selecting cpu.

for example we have 50 DI/O adn 50 AI/O and x no. PID input and y no. of valve and etc. then what will be equation or formula about cpu.