Which PLC/HMI platform should I choose?

Read what The Experts had to say to a reader's question regarding which PLC and HMI platform to choose for their particular process plant automation and controls applications.

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Ask the ExpertsQUESTION:

I WOULD like to ask for your comments and suggestions. I have volumes 1-3 of your Instrument Engineers' Handbook" and find them to be an excellent source of technical information.

We’re constructing a large wallboard manufacturing plant in West Virginia. We’re currently at the crossroads of deciding whether we go with Siemens’ S7 PLC and WinCC HMI platform, or Rockwell Automation’s Allen-Bradley ControlLogix PLC and Wonderware’s InTouch HMI platform for the plant automation and controls.

We’re presently collecting data, and analyzing the pros and cons of both systems. Some areas of special concern are: automation performance comparison; software friendliness and ease of use; local plant technical support availability; availability of personnel resources familiar with either system; networking superiority; automation superiority; and price comparison. Any specific comments/suggestions you may have would be highly valued for someone trying to decide between the two systems. 

Sam Roe, Senior Eectrical/Automation Engineer, BPB America


ANSWER:

THE ARCHITECTURE of the system is important. This applies to hardware architecture as well as software architecture. The central component of the hardware architecture is the control-network. Without a doubt, this should be based on standard Ethernet. I stress standard Ethernet, not modified "industrial" Ethernet, which requires specialized hardware, and which doesn’t use IP. For availability, it’s important that true, duplicated "DCS style" redundancy is supported, not just ring topology. The application protocol on top of IP is critical for interoperability between devices from different manufacturers, as well as package unit integration.

Do not go for proprietary protocols over Ethernet and IP. These criteria pretty much narrow the control-network platform down to Foundation fieldbus’ High-Speed Ethernet (HSE). Siemens doesn’t support HSE. Allen-Bradley does to some extent, but there are other options you should examine.

At the core of the software architecture, you need a technology to exchange data between hardware and software, and between the different software applications. Undoubtedly, this should be OPC, including the principal flavors OPC-DA, OPC-A&E, and OPC-HDA. Both Wondwerware and WinCC support at least OPC-DA. Wonderware maps it to its own solution, loosing some of ease of use, though this situation could have changed. I have no experience with WinCC.

In addition, there are other options you should explore, and other software technologies you should make sure are supported. These include: SQL/ODBC/OLE_DB/ADO database access; ActiveX graphics components and OLE container; DDE for legacy; VBA for script; and HTML for web viewing, etc.

For OPC and other software technologies take a look at the book "Software for Automation: Architecture, Integration, and Security.” For Ethernet, take a look at the book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance." 

Jonas Berge, SMAR


IS THERE some reason you've limited your evaluation to the two combinations indicated? A good reason might be that there's already experience with all of these products elsewhere in your company. On the other hand, if there's not a particularly strong reason to impose such a limitation, you might want to include at least a couple other possibilities:

  • In the PLC area, Modicon (Schneider Electric) especially, and perhaps GE Fanuc as well.
  • In the HMI area, Intellution’s iFix (now owned by GE), and RSView32 (Rockwell
    Automation/Allen-Bradley), and perhaps CiTect, too.

As for PLC's, I have personal experience with Modicon (584, 984, Quantum) and Allen-Bradley (PLC-5, SLC-500, ControlLogix) in pulp and paper and food industry applications.  I’ve found both to be solid products, but have I a slight preference for Modicon.

As for HMI's, I have personal experience with Wonderware and Intellution, more hands-on experience with Wonderware, and a slight preference for Intellution for technical and commercial reasons.

This may not have helped because it’s more opinion based on personal experience. My Modicon preference comes from early days employed in the Cellulose and Specialties division of Procter and Gamble, where we chose Modicon over Allen-Bradley as the standard for that division of the company because it could better meet higher performance requirements in the pulp and paper mills.

Of course, keep in mind that most leading HMIs will integrate well with most leading PLCs. There may be some minor advantages in pairing ControlLogix and RSView because both are Rockwell/A-B products.

R. H. (Rick) Meeker, Jr., P.E., Reliable Power and Controls Corp./Process Control Solutions, Inc., Tallahassee, Fla.

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