In recent years, the choice between PLC and DCS for controlling processes has been blurring more and more in the perception of the system owners as the functionality of the two realms continues to overlap and grow together. Evidence of the ongoing battleground is present within a number of groups and discussions on LinkinIn.com right now. The term “hybrid” has now been used for a number of years to describe the middle ground application space that seems to be looking for a clear winner to be able to select between the two choices.
Now there may actually be a little more “science” to help those of you trying to make this choice, especially those with needs that reach beyond basic control to include batch, ERP integration, redundancy and other higher function requirements. A colleague of mine passed me this link to anarticle published on Control Engineering Europe Online in March, that those of you interested in this topic may find as an intriguing read.
Especially in those hybrid applications, the choice may seem obvious that lower cost hardware and software PLC systems would be the more cost effective solution. However, the author covers seven (7) areas comparing and contrasting PLC and DCS characteristics on topics that go beyond the simple cost quoted in a response to a specification:
- System design
- Programming
- Commissioning and start-up
- Troubleshooting
- The ability to change to meet process requirements
- Operator training
- System documentation
The outcome may still not be “crystal clear,” but the results presented may help provide some insight into issues and concerns that many projects often overlook and neglect to consider when making the purchasing choice.
Hopefully some of you will find this interesting and useful. If you do, please join the conversation and comment back to me. Others will be interested in your experience or perspective too, so please share.