Furthermore, purchasing a PLC allows you to buy only the software with the features you need. PLCs grew up as replacements for multiple relays and are used primarily for controlling discrete manufacturing processes and standalone equipment.
If integration with other equipment is required, the user or his system integrator typically has to do it, connecting human-machine interfaces HMIs and other control devices as needed. The DCS, on the other hand, was developed to replace PID controllers and is found most often in batch and continuous production processes, especially those that require advanced control measures.
The vendor handles system integration, and HMIs are integral. As users demanded more production information, PLCs gained processing power and networking became common. The DCS supervises the entire process, much like the conductor in an orchestra. Protocols, like OPC, have eased interactions between the two control systems.
The answer, like most things in the world of automation, is that it depends on the needs of your application. Here are six key factors to consider:. PLCs are fast, no doubt about it. Response times of one-tenth of a second make the PLC an ideal controller for near real-time actions such as a safety shutdown or firing control. In fact, safety systems require a separate controller. Another problem with PLCs is redundancy.
The complex nature of many continuous production processes, such as oil and gas, water treatment and chemical processing, continue to require the advanced process control capabilities of the DCS. If your process is complex and requires frequent adjustments or must aggregate and analyze a large amount of data, a DCS is typically the better solution. DCS vendors typically require users to employ them to provide integration services and implement process changes.
System integrators perform similar functions for PLC-based systems. Another problem with PLCs is redundancy. The complex nature of many continuous production processes, such as oil and gas, water treatment and chemical processing, continue to require the advanced process control capabilities of the DCS. Others, such as pulp and paper, are trending toward PLC-based control.
If your process is complex and requires frequent adjustments or must aggregate and analyze a large amount of data, a DCS is. DCS vendors typically require users to employ them to provide integration services and implement process changes. System integrators perform similar functions for PLC-based systems. It has also become common for PLC vendors to offer support services through their network of system integrator partners.
Process control has become increasing complex. Manufacturers also continue to reduce factory staff and a generation of experienced process control personnel has begun to retire. As a result, the quality of support has become a critical factor in vendor selection. Liked this article? Download the entire playbook here. Here are six key factors to consider: 1.
Response time PLCs are fast, no doubt about it. In what cases is it clear that we should go to the DCS solution? If we meet the following requirements the solution will probably be the DCS:. In what cases is it clear that we should go to the PLC solution? In this case we will have to do an analysis of our case and evaluate our standards and requirements.
This simple OS structure means they can execute programs quickly because there are not many other processes running in the background and demanding time from the processor. PLC processing times are also quicker because they are naturally closer to the devices they control motors, pumps, switches, etc.
PLCs are generally flexible and more readily customizable as well. On the other hand, a DCS can control many more machines and processes at the same time.
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