DCS v. PLC/SCADA

We kicked off the blog and video series talking about the Intelligent Automation Pyramid. Part of that was specifically talking about PLC/SCADA v. DCS and that video was extremely well received, thanks everyone for that! So we’re going to talk about that in some more detail.

 

In the past, SCADA was much more of a data acquisition and less of a control system. So if you wanted/needed control, you’d specifically look into a DCS. There have been many technological advances causing the lines to be blurred.

Now SCADA has the control side down without issue. In an effort to present the best overall cases, we won’t be getting into any specific details of SCADA’s or DCS’s, but will be extrapolating on our overview in order to give everything the best information possible.

The question becomes the differences between a PLC/SCADA and a DCS. They come down to two major factors 1) Customization of the system and 2) Choices in hardware and software.

Customization:

Is a double edged sword. A PLC/SCADA system, has much more work that is involved with set up. All the PLC I/O must be set up individually, plus the programming that must be created to actually control the system. This will allow for the most flexibility with PLC’s and I/O modules, and a PLC can be used for virtually any machine or line, it will also take more time. The SCADA must be built, and it can be built the exact user specifications. Corso likes to say that if you can dream it, we can build it. That’s very true, the more customization that is required the more time it will take and that also correlates to the cost at the end of the day.

A DCS takes much less time and programming ability to be able to set up correctly. A manufacturer is going to offer a DCS and everything else that you need to be able to set up the system from controllers to cables. The downside to that is you need the correct controller to be able to control your specific process and one for all the different processes in the facility. You’re also going to be able to get the functionality out of the DCS that is built in and not much else.

Choices:

A DCS is going to have a propriety hardware and software. You are going to be able to use the software and the controllers that they offer. A facility is not going to be able to pick the Honeywell DCS, but use Emerson Delta V controllers. The DCS’s are set up in a way to keep everything in the same ecosystem.

The PLC/SCADA options provide (virtually) limitless options. 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’re looking for.

What Do You Want?

That’s a very personal question. Alex and Evan are working at a facility that has a Delta V DCS installed (because it’s legacy equipment). One should always look at all their options. The best piece of advice that we can give is if you’re looking at a new installation, or a retrofit, there would need to be a really, really good reason to go DCS over a PLC/SCADA system.