selcting control system for 100tpd oxygen plant


Thread Starter


can it be right choice of selcting plc for controlling analog loops for oxygen plant. no.of analog loops 12 all are control loops

please guide me

we are going to convert 100tpd oxygen plant from
pneumatic control system to electronic control

we have in our plant 12 analog control loops, can it be right choice to implement it by plc .

can anybody tell the difference in selecting dcs
and plc for controlling analog loops

Manesh T.Varghese

Dear friend ,

It will be OK if you are having only 12 control loops and you are not planning to increase it in the near future in the form of a any
developmental activites.The PLC will give you basic PID functionalites with limited tools for analysing the production and process.Running
it with some optimisation packages and and connecting it to enterprise solutions will be not that easy if you go for a PLC.Advanced PID
facitlites like adaptive controllers will not be available in most of the PLCs.

You can go for systems like Freelance of ABB which integrates both DCS and PLC in a single
system.It is a cost effective solution.

Manesh T.Varghese
I would use as many controllers as possible all with their own mmi to keep short lines and controls modern controllers talk by modbus to central machine to have nice graphics etc. I would not dismantle the pneumatic system, i would use it and have the controller giving 4/20mA to a I/P converter. This way you can operate the plant any way.
The short answer is yes a plc can perform the tasks you need and many can offer significatant room for growth. You should choose one that
supports programming with IEC languages and Function Block Diagram for your loops. The PLC can save you significant money when compared to
a DCS and Today many PLCs offer the same power as a DCS. One that I would look at is Modicon Quantum programmed using Concept v2.5
software, but I am probably biased.

Parag Bhadra

You could use a Siemens S-7 PLC for the realtime functionalities and a PC front end with Citect HMI software for Graphics.

You could also hook up into a more sophisticated control system later.

Parag Bhadra
Metso Minerals
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DLF City Phase III
Gurgaon, Haryana
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I just joined the group and this is my first response. I hope it is of value. First, realize that if you keep the pneumatic system in line you increase install cost (at least 24 new I/Ps) and increase error. Keep in mind that one of the benefits in moving from pneumatic to electronic control is to improve measurement/control accuracy. However, if electrical service availability is questionable the pneumatic backup may be worth the trade-offs.

Second, in lieu of a PLC or DCS you might try one of the smaller hybrid controllers. I recently became aware of the Honeywell UMC800 which will do 16 complex PID loops, uses graphical function block programming, and has a remote mount panel LCD operator interface included. It is the right size as long as you are not planning a lot of future expansion and the cost is low compared to
PLC/DCS/software, etc.
I would use a Modicon Quantum with Concepts 2.5 and Citect as the HMI. I have done several systems this way; 1 with 10 PID loops and 1 with 19 PID loops. Trash the Pneumatics, they will just give you more problems, and more errors.