Total Fustration - PLC vs DCS

I agree with Mike and Jesper here.

The key is to get your terminology straight. Different industries and professionals regard "DCS", "PLCs", and "SCADA" as different things. The lines are converging with Internet technologies. Do TCP/IP enabled PLCs on a geographically separated regions constitute a DCS system? What DCS system are you referring to that's "more capable" than what PLC system?

BTW, your list represents software, not hardware, which is what PLCs and DCS are.

Production Scheduling/ Accounting
üExpert System/Statistical Process Control
üProcess modelling
üAlarm Handling/Rationalisation
üPredictive Maintenance

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Biggest advantage of our Foxboro DCS is the redundancy it provides in processors and communications. Basically you need two failures to have an impact on the plant.

cornbread said:

Biggest advantage of our Foxboro DCS is the redundancy it provides in processors and communications. Basically you need two failures to have an impact on the plant.

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Processor and communication redundancy is perfectly achievable in PLC based system too. Example S7 414-H.

Don't we get this type of discussion every year?

I came from a DCS background.

To me, the best analogy is that a DCS is like using Windows and PLC is like doing assembly language. PLC can do everything a DCS can do but do require more planning to have a structure that's easy to support.

It's a lot easier to get into messy logic in PLC while DCS already has a built-in structure in keep everything clean.

yes, DCS is a lot more $$$ but it's worth it in most continuous process environment like a refinery.

Just my 2 cents.

harryting said:

Don't we get this type of discussion every year?

I came from a DCS background.

To me, the best analogy is that a DCS is like using Windows and PLC is like doing assembly language. PLC can do everything a DCS can do but do require more planning to have a structure that's easy to support.

It's a lot easier to get into messy logic in PLC while DCS already has a built-in structure in keep everything clean.

yes, DCS is a lot more $$$ but it's worth it in most continuous process environment like a refinery.

Just my 2 cents.

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Guys,
Your comments have helped me a lot. Thank you.
Ours is a big oil platform on GE Fanuc 90-70 and 90-30 PLC based DCS. Thease PLC's were built in 1990. Looking into the future, if we have to upgrade then it would be better to go for a DCS rather than to another type of PLC (RX7i, RX3i). Please share your views.

Attached filed sheds some light on DCS and PLC control altough emphasis is on DCS system.

jaichains said:

Guys,
.........Thease PLC's were built in 1990. Looking into the future, if we have to upgrade then it would be better to go for a DCS rather than to another type of PLC (RX7i, RX3i). Please share your views.

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Financially it would not be the better move. IF all you need to do is upgrade the HARDWARE the 9070/9030 programs can be ported to the Rx7i/Rx3i counterparts with little hassle. The PLC Programming software (Proficiy Machine Edition) will convert the existing 9070/9030 project from one platform to another providing you a detailed list of potential issues that may need to be addressed. 95% of the 9070/9030 IO modules can be re-used in the Rx7i/Rx3i systems so you minimize the hardware costs, and you have very minimal programming costs (to correct any conversion issues). You also minimize downtime as swapping the PLC backplanes and modules is a snap, and if there is a problem, put the old PLC back in place and your can live to fight another day.

I'm currently in the process of doing this as the plant cannot be shut down for an exented period for a complete retrofit, and they do not want the cost of a complete retrofit.

If you NEED to re-write code to better optimize your process, if you have an endless budget, and if the system can be down for days/weeks for install/testing of a new DCS system, then hey it may make sense to completely strip out the old PLCs.

But it sounds like your heart is set on a DCS system.