How DCS and SCADA Systems Differ from One Another

Rachel Smith, Applied Technology Review | Thursday, May 19, 2022

DCS and SCADA systems transform in tandem with broader digital transformation themes, such as the Industrial Internet of Things (IIoT).

FREMONT, CA: Industrial control systems have played a significant part in industrial automation for decades by enabling process manufacturers to gather, process, and act on production floor data. These systems are currently in transition. DCS and SCADA systems may now assist digital transformation due to ongoing technological and industry advancements.

Typically, process manufacturers utilize DCS and SCADA technology to monitor and control facility operations. The DCS was created to replace analog and pneumatic loop controllers, which were troublesome for extensive processes in refineries. SCADA was initially developed to solve activities spanning vast geographical areas, such as pipelines and utilities. Later, a variation utilizing HMIs in conjunction with PLCs for industrial automation applications arose.

Nevertheless, DCS and SCADA systems are no longer limited to monitoring and controlling. They are merging with extra intelligence at every level of the industrial automation architecture to support predictive asset lifecycle management and value chain optimization while also enhancing the experience of stakeholders and improving security and safety. Although this particular industrial control system change is already in progress, the bigger transformation of industrial automation systems has only begun.

The differences go well beyond the fact that a typical SCADA system may work with a vast area network with significantly lesser capacity than a DCS local area network.

A DCS uses dispersed workstations for operator HMI is a fundamental distinction. Each workstation can interface directly with DCS network controllers. All communications between HMI workstations and PLCs will be routed through a server in a SCADA system. Thus, the server is a single point of failure, which might render the entire process invisible to all users.

While the architecture of a DCS and a SCADA system may appear identical at first glance, the DCS adds several, often subtle elements, such as redundant electronic circuits, which boost system availability and minimize downtime. All distant I/O electronics and communication networks between them and the DCS controllers are redundant or may be optionally redundant.

While SCADA HMIs and servers are primarily commercially available off-the-shelf (COTS) PCs, a DCS employs non-COTS, task-optimized components. In addition, a DCS isolates the Windows operating system from the process, which improves security. A deterministic DCS LAN ensures that a vital message, such as a high-priority alarm will reach its intended recipient. Typically, the SCADA system relies on the high bandwidth of the LAN.

Since a single DCS vendor supplies the entire system, controllers and workstations are more tightly linked in a DCS than in a SCADA system. Expected benefits include lower engineering costs and simplification. Still, a DCS will be more expensive than a SCADA system for a given process, but the price difference is justified for operations where unscheduled shutdowns are incredibly costly. Although SCADA suppliers could add redundant servers or high availability computing platforms to improve the reliability of these systems, their availability will be lower than that of a DCS.

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