PLC and SCADA Systems

can You please elaborate more

We had a Rewinder which was using the Mode bus. It was replaced with Simens ET200 distributed IO. No downtime since then.

Sounds interesting !! KIS - Keep It Simple is the best bet...

Appreciate more details please.

Hard to answer but

keep it simple is rule numer one

the smaller amount of information in one wire the easier to fault find

therefor if using any network comms of any type i.e. modbus, then you complicate fault finding...but you said this is not being used for control so why is a comms fault stopping the plant? (this to me is the question that needs answering)

on the other side of the coin you could always

improve system diagnostics to show what the real fault is...i.e. filter alarms so when plant stops due to comms fault only the comm fault alarm is shown.

good luck

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Guest,

Perhaps if the technicians had been properly trained then the downtime would not have been so long. Proper training is typically the first thing to be cut back on, you need to look at the quality of the training and the aptitude of those being trained.

Keeping it simple is the best policy. I would advise you to have a programmer develop a life-like screen model(in color like panelview) of your process with permissives and when the systems faults, have the life-like screen model pinpoint the faulted part and area. This will make the troubleshooting a lot easier and reduce the production downtime.

I to maintain a pollution plant that has been individually cabled and numbered to each field device ,the company has NO drawings for the system at all and yet because of the way it has been done I can find any device or fault that occurs on the system so I am very much in favour of the KIS method especially in a plant where the corrosive fumes are even eating the concrete floor.

Actually it does not matter if you have hardwired, Modbus, Devicenet or wireless sensors as far as troubleshooting time goes. (although any of the above can add to number of problems to be found. Like Modbus communication going out.)

The two primary factors in troubleshooting with a PLC is training and documentation. Using a PLC, it typically takes 5-10 minutes for a properly trained technician with discriptored ladder logic and an electrical layout diagram, to find a problem, no matter how complex the system. Time to fix varies on actual problem found.

Items that can increase troubleshooting time in order of most negative effect are ...

· Lack of proper training.

· Lack of proper PLC program documentation.

· Over complicated PLC ladder logic.

· Lack of electrical layout and schematics.

System Designs in order of most timely to troubleshoot are ...

· DCS (Mostly proprietary and designed for only OEM to use.)

· SCADA (Often proprietary, non-user friendly and training deficiencies. Seek Wonderware® and Factorytalk® training.)

· PAC (Ladder Logic easy, but function block diagram is not always, structured text is a more complex computer programming language.)

· PLC (Ladder Logic, easy for electricians and mechanics too if tought properly.)

The bottom line is that all the above systems could be easy (quick) to troubleshoot if one is constantly trained, the system is well documented and designed for the laymen to easily understand.

Hi all,

This is going to open up a huge can of worms.

There are many reasons and standards that will require the use of hardwired interlocks esd's etc.

You say that you are working in a process plant - that unfortunately does not give us much information. A refinery is a process plant - and you will not be able to get away with your current method of design in that environment.

If your drawings and documentation are up to scratch - your technicians should have no problem with the fault finding - provided they are competent in what they do.

Utilising bus systems etc is not necessarily more complex. There are many rules that govern the methods for selecting the correct bus system for the correct application, environment and the installation of this bus.

If done correctly, the amount of information that is made available from smart transmitters is invaluable and will save you many $'s in the long run.

I have come across many bus installations where they have had problems because of installation issues. In all of the cases - the people who designed the initial system had no idea what they were doing.

A bus is not evil, and neither is conventional wiring. Both have their place in the system. Sometimes they have to be combined to complete the overall system.

So my short answer to you - there is no "better" strategy. You need to understand the legal requirements of your "process" plant to determine the type of system to put in place.

Regards,

Craig