Redundancy System Using Modicon

Hi All,

I am requested to build a redundancy system for my PLC.
May i have a headlines of what should i do?

The PLC is Modicon M340 from Schneider Electric.

Should i put a second PLC? How should i control the 2 PLCs and connect the input/outputs?

Thanks

With all due respect, if you have to ask such a basic question, you are probably better off purchasing a redundant controller system rather than trying to create one yourself.

There are several different levels of redundant controller systems. Your first step is to define exactly what you hope to accomplish. Then contact your PLC supplier and see what they have to offer.

I have made a full program with a PLC and SCADA for a water project, and the consultant asked me to build a redundancy system.

I am assuming i should put a new plc with all modules and make jumpers with the old one. and activate either of them using a selector switch or something like that right?

wouldn't this make any problems on the input/output?

Regards

wouldn't this make any problems on the input/output?

Click to expand...

Redundant controllers may seem like a simple thing in concept, but there are many pitfalls for the uninitiated when it comes to putting a redundant system into operation.

If you want a backup system to minimize downtime, buy enough spare parts so that you have at least one of every part number. Keep your backup CPU module loaded with the same version of logic as is running on the primary system.

For anything more sophisticated than that, I repeat what I said earlier. Since you are asking such basic questions, you will be better off purchasing a system from a supplier with enough experience in redundant systems.

Eyad sent me a private message.

you cannot at least help me with the headline of the pitfalls that might come if i made had to install 2 plcs?

I would truly appreciate your help

Click to expand...

All right, here are a couple of things to think about.

Suppose you have two PLCs simultaneously connected to the same I/O modules. How do you determine which PLC is actually in control of the outputs? In other words, if one PLC tells an output to turn on, but the other PLC tells the same output to turn off, which PLC does the output point obey? How do the two PLCs know which one is controlling the outputs? How do they know when to switch roles?

If you have an HMI panel connected to the system, how does the HMI application know which PLC to communicate with for display data? When an operator changes a value or touches a control object on the HMI panel how does the HMI know which PLC to send the command to?

If one PLC has been out of service and you're bringing it back online how can you be sure all the data in both PLCs is synchronized? For example, let's say the primary PLC is in control and the backup PLC has been shut down and now you're going to start it. Let's also say you have some latch instructions in your ladder logic and a few of those latches are in the ON state, but the logic contolling both the latch and the unlatch is false, meaning the reason the latch is ON is because its a latch and you haven't specifically told it to be OFF yet. Given that scenario, how will the backup PLC know that it should turn the latch bit on?

That is by no means an all-inclusive list. Just enough to start you thinking.