The differences go much beyond the fact that a conventional SCADA system can function with a wide area network that has substantially lesser capacity than a DCS LAN.
A significant difference is that a DCS employs dispersed workstations for operator HMI. Direct communication with controllers on the DCS LAN is possible for any workstation. All connections between HMI workstations and PLCs in a SCADA system pass through a server. Since the server is a single point of failure, it’s possible for it to fail, making the entire process invisible to all users.
Despite the fact that the design of a DCS and a SCADA system may otherwise appear to be the same, the DCS has many additional, frequently subtle features that improve system availability and reduce downtime, such as redundant electrical circuits. Remote I/O is included in redundancy. The communication networks between the DCS controllers and remote I/O devices are redundant, or at the very least, they have the possibility to be. On the other hand, a PLC is made with hardware cost reduction in consideration.
A DCS uses components that have been designed specifically for the purpose and are not commercial off-the-shelf (COTS), unlike SCADA HMIs and servers, which are commonly comprised of COTS PCs. The Windows operating system is also maintained separate from the process in a DCS. Thus, cyber security is improved. A predictable DCS LAN ensures that important messages, including high priority alarms, will reach their intended recipient. Instead, the SCADA system often uses the LAN’s high bandwidth.
Components like controllers and workstations are more tightly integrated in DCS systems than they are in SCADA systems since a single DCS vendor generally provides the whole system. Benefits like simplicity or lower engineering costs are typical. Nevertheless, a DCS will cost more than a SCADA system for a specific procedure. The price differential makes sense for operations where unscheduled shutdowns are extremely expensive. While SCADA vendors might use high availability computing (HAC) platforms or redundant servers to make such systems more dependable, their availability will not be as high as that in a DCS.
Despite the differences between DCS and SCADA, both of these system types are evolving in step with more general DX trends, such as the integration of the Industrial Internet of Things (IIoT). The promise of this change is enhanced industrial automation capabilities and benefit for process makers.
Vendors are rethinking operational technology (OT) automation systems employing commercial-off-the-shelf (COTS) and information technology (IT) components in response to new concerns that end users have raised. End users demand that manufacturers deploy best-in-class COTS hardware and software to build automation systems that outperform the current DCSs in terms of dependability, security, and end-user value.
They also want a solution that enables them to transfer their control tactics onto updated or new systems while still maintaining those techniques. Additionally, end users have sought modularized hardware components for incremental upgrades, such as compute, networking, storage, and I/O terminations. Finally, they want software that can run anywhere in the system and is independent of the hardware and I/O.