% IO reserved in PLC

[sapoleon]

Hi,
Long time not participate...
I hope that will change in the near future.

I have just one question,
How do you calculate the reserve percentage that you leave in a PLC.

the amount of free IO / used IO
or
the amount of free IO / total IO

(of each class obviously)

Thanks for your inputs.

 

[RussB]

Neither, just have at least 3 empty slots with at least one in the CPU rack, if rack I/O. Or the ability to add 3 nodes in a remote I/O system, preferably anywhere in the network.
If a customer wants more follow their spec and charge them for it.
Of course it is always nice to have a few I/O not used just in case somebody forgot something.

 

[mendonsy]

It depends entirely on the application.
Sometimes 10% is enough, but when there is a potential for future changes it requires much more.
The system I am doing right now has 25% spares with expansion capability of more than 5 times what is now installed.

 

[shooter]

example
free 25% used 75% first line means 1/3= 33%
second line is 1/4 = 25%
free space depends fully on application (i try to use 0%) as customer has to pay for something he does not get. and maybe in the future will need. and yes all systems are expandable so no need to sell bigger as needed.

 

[sapoleon]

hi,
thanks for the input.
it´s a new plant, and i´m checking the engineering.
I know is not something fixed, but... just wanted to know if there was a "normal way" of looking a it.

 

[Lancie1]

If you are the customer, then I would hope to have at least 20% spare Input and Output points. If I am the contractor or plant builder, Then I try to get about 10% spare I/O. If you have no spares at all, then revisions made during construction become very expensive for all parties.