SCADA or DCS?
Published on : Tuesday 07-03-2023
PV Sivaram on the continued relevance of DCS and why it is far from dead even in the IIoT era.
Anand is freshly back from visits to exhibitions. Yes, exhibitions, in plural, since he has been to Germany as well. He looks drowned in the sensory inputs – lights and sounds, and the hype. He was trying to recount all the interesting new things he had encountered. I would like to focus on a particular statement. He tried to explain to me that DCS is dead. Why? How? I interject. Anand explains – SCADA has become so powerful, there is no need for a DCS anymore. I get a little worried, since ahead lies a complex field. As with every evolutionary process, Operator Information Systems too traced a torturous twisted path over the decades, with many blind turns, dead ends and backtrack. How does all this look for an engineer who will graduate into a world of IIoT and AI? And even more, for an engineer will probably be employed in a plant equipped with legacy tools, but wanting to rapidly move to the twenty-first century technologies.
There is no way out. We need to trace the history. In the beginning, there were the logic boards with logic embedded in the way relays were wired. This logic in wiring was depicted as a ladder, each rung of the ladder with several relays wired in ingenious ways to execute sequential functions and interlocks. Relays being what they are, the logic was binary logic or digital logic.
At a later date, as Integrated Circuit chips (ICs) with VLSI came to existence, controllers based on microprocessor chips came to replace the clumsy relays. Logic was implemented as programs. So these devices came to be known as Programmable Logic Controllers or PLCs. The happenings in the process or in the controller were communicated by LEDs and audible alarms. Each machine or process was working in isolation. Well, not really in isolation, because the commands and production planning and so on had to be centrally made and implemented on all machines. So a strong need was felt to have a central command station for the supervisor or manager, to have an overview, as well as to issue commands.
In early days, PLCs would handle only digital logic (as a natural successor to the relay logic circuits). Process industry needed closed loop controls which could handle analog signals. There were special boards with these capabilities to accept analog inputs and outputs. As time passed, more specialisation was built in and cards to deal with specific control loops like a temperature control or flow control, etc., were created. One single card could perform the closed loop controls, access the alarm conditions, and as the card became more and more intelligent, could even calibrate the sensor. So there was a clear cut distinction between PLC and DCS in terms of the features and yes, pricing as well.
As this was going on, ICs became more dense, processors became more intelligent, memory capacity increased, and soon there was no such clear-cut distinction in terms of hardware. But the DCS systems had built up a comprehensive system of libraries for each application domain and so maintained their lead.
Both PLC and the DCS needed a means to communicate with the humans. The PLC systems would communicate with a PC. The software on this PC acquired its own features and this SW was SCADA. SCADA stands for Supervisory Control and Data Acquisition. Pretty soon there was a confusion of names and terms – Digital Control Systems, Distributed Control Systems, Data Acquisition Systems, and SCADA systems. There is no very strict differentiation as on date among these systems. The underlying control hardware is also largely uniform.
As we enter into the era of Industry 4.0, this model of centralised information flow is no longer the preferred mode. The DCS or SCADA looks like a hub and spoke model. In the I4.0 era, we look for a more democratic model, where information is available everywhere to everybody. We do not want to walk into a control room to know plant status. We do not want morning updates via phone call from the night shift operators to the plant managers. IIoT provides that the information is available on a smart phone on a continual basis.
If we look a little further into the future, with the help of Augmented Reality, one can even undertake a walk through a plant from wherever one just happens to be.
So Anand, the evaluation is not between SCADA and DCS, both of which are a generation old. The challenge for designers of the information delivery systems is to incorporate IIoT and AI into the plant logic and deliver the results and prompts for human intervention using AR/VR. Human intervention need not be by pressing buttons or touch pads, but by voice or gestures.
PV Sivaram, Evangelist for Digital Transformation and Industrial Automation, is mentor and member of steering committee at C4i4. He retired as the Non-Executive Chairman of B&R Industrial Automation and earlier the Managing Director. He is a past President of the Automation Industries Association (AIA). After his graduation in Electronics Engineering from IIT-Madras in 1976, Sivaram began his career at BARC. He shifted to Siemens Ltd and has considerable experience in Distributed Systems, SCADA, DCS, and microcontroller applications.
Sivaram believes strongly that digitalisation and adoption of the technology and practices of Industry4.0 is essential for MSME of India. He works to bring these concepts clearer to the people for whom it is important. He believes SAMARTH UDYOG is nearer to the needs of India, and we must strike our own path to Digital Transformation. Foremost task ahead is to prepare people for living in a digital world. He is convinced that the new technologies need to be explored and driven into shop floor applications by young people. We need a set of people to work as Digital Champions in every organisation.
