PLC vs. DCS: Which is Right for Your Operation?

PLC vs. DCS: Which is Right for Your Operation?

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When it comes to industrial operations, there’s a massive debate on whether you should go with using a PLC-Based system or Distributed Control System – DCS for Short. Some experts have tried to sort this out for you.

Distributed Control Systems (DCS) is inevitably the primary solution for process automation. But nowadays, a huge fraction of PLC vendors are pursuing these applications with an argument that a single integrated architecture based on PLCs seem to have the best approach to total plant automation.

You must be wondering about the difference between distributed control systems (DCSs) & programmable logic controllers (PLCs). Let’s understand this using a simple football metaphor. DCS is actually the team captain; it’s dependable and hardworking that controls the entire outfit. Whereas, the PLC is a utility player, who doesn’t mind where he plays, but you also can’t expect PLC to be as reliable as the captain.

Over a decade, different control systems functionality has been merging. Nowadays, Programmable logic controllers (PLCs) have all the capabilities that were once found only in the distributed control systems (DCSs). While the DCS is able to handle many functions previously, it’ll be more appropriate for PLCs as well.

Inevitably, the PLC was meant to be a replacement for multiple relays and is used primarily to control the discrete manufacturing processes as well as standalone equipment. In case the integration with other equipment is required, connecting HMIs – the human machines interface and other control devices as required.

Nowadays, the PLCs aren’t that much expensive and can now perform much like DCS. Perhaps that’s the reason why it’ll be good to convert everything to PLCs for some of the automation – not all. If you are wondering about whether you should go with PLCs or not, well honestly, it depends on the applications actually. While dealing with this, here’re a few significant factors that you must consider; 

Response Time

Undoubtedly, PLCs are fast – way faster than other alternatives. Response times of 1/10th of a second make the PLC the right controller for real-time actions like a safety shutdown or even firing control. DCS takes way longer to process the data. Perhaps that’s the reason why it doesn’t seem to be the perfect solution when response times are critical. Therefore, the safety systems require separate controllers.

Scalability

Primarily, PLC is only able to handle a few thousand I/O points or maybe less. That’s why it’s not as scalable as a DCS that’ll handle many thousands of I/O points while easily accommodating new equipment, process enhancements and – on top of all – the data integration. In case you need advanced process control and you already possess a large facility a process spread out over a wide geographic area with 1000s of I/O points, a DCS would be much more suitable.

Redundancy

When it comes to PLCs, redundancy is another major problem that you have to deal with. In case you really need power or fault tolerant I/O, just don’t force the requirements into a PLC-based control system. This way, you will end up raising the costs to equal or perhaps exceed those of a DCS. While dealing with the DCS, one has to have proper and complete knowhow of Valves, Actuators & Regulators Courses in order to ensure efficiency.

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