DCS versus PLC/SCADA
Recently, we kicked off our Intelligent Automation Pyramid blog and video series. Part of it discussed using PLCs and SCADA vs. DCS. The video on that topic (watch below) was extremely well received—thanks, everyone for that! So, we figured that it was time to talk about using PLC/SCADA vs. DCS on its own in more detail.
In the past, SCADA (Supervisory Control and Data Aquisition) systems did more data acquisition than control. Back then, if you wanted or needed control of your facility and machinery, you’d specifically look into a DCS (Distributed Control System). But now, many technological advances have blurred the lines.
Now, SCADA has the control side down without issue.
To present the best overall cases, we don’t need to detail SCADA systems or distributed control systems, but will be extrapolating on our overview to give everything the best information possible. The differences between a PLC/SCADA system and a DCS come down to two significant factors:
Customization of the system
Choices in hardware and software
DCS vs. SCADA Customization:
Customization is a double-edged sword. There’s much more work involved setting up PLC and SCADA system: every PLC I/O must be set up individually, then you will need to create the logic to control the system. While this allows for the most flexibility with PLCs and I/O modules—and a PLC can be used for virtually any machine or production line—it will also take more time. The SCADA must be built, to match the exact user specifications. At Corso Systems, we like to say that if you can dream it, we can create it. And while that’s very true, the more customization required, the more time it will take—and that also correlates to the overall cost at the end of the day.
A DCS takes much less time and programming skill to set up correctly. Equipment manufacturers will offer a DCS and everything else that you need to set up the system from controllers to cables. But, the downside is that you will need the correct controller for each specific process—and different controllers for each and every different operation in the facility. And while you will have the basic built-in functionality of the DCS, that is all you will have available!
Hardware and Software Choices:
A DCS has propriety hardware and software, and you will have to use only the software and controllers that they offer. A facility will not to be able to pick a Honeywell DCS, but then use Emerson Delta V controllers. A DCS is set up so that it keeps everything in the same ecosystem.
The SCADA and PLC options provide nearly limitless opportunities. If you want to use Siemens S7-1500 PLC’s, with Rockwell Panel view HMI’s, and Inductive Automation’s Ignition for the software, you can do that—and it will work well. If at some point you want a third party HMI or a different PLC, those can (basically) be pulled out and replaced with what you need.
What Do You Want?
That’s a very personal question. At the time this post was originally written, Alex and Evan were working at a facility using a Delta V DCS (because it’s legacy equipment). The best advice that we can give: if you’re looking at a new installation, or a retrofit, there needs to be a VERY good reason to choose a DCS over a more modern PLC and SCADA system. Otherwise you will have more flexibility and upgrade potential with a SCADA and PLC setup.