The Importance of System Robustness and Stability in Distributed Control Systems

Author photo: David Humphrey
By David Humphrey


The influence of information technology (IT) on operations technology (OT) has many benefits, but does web-based engineering make sense for a distributed control system? Configuring a DCS in a browser would have been unthinkable just a few years ago, but Distributed Control Systemstoday it is an integral part of Siemens’ SIMATIC PCS neo.

This ARC View is part of a series of reports that look at various innovative aspects of Siemens new concept for process automation in the areas of operator empowerment, collaboration engineering, and system robustness.

Robustness and Stability

Process plants are complex facilities that transform raw materials such as natural gas into a variety of products for further processing downstream. Because of the high upfront capital costs, process plants are built to run for several decades. To operate profitably over a plant’s long lifecycle requires a robust, expandable, and scalable distributed control system (DCS).


Plant availability and equipment uptime are the highest priorities in most process plants. For continuous processes, unplanned downtime is expensive – often thousands of dollars per minute. Some processes take a long time to restart and even longer to return to pre-stoppage quality levels.

For distributed control systems, “robustness” means not only features for rugged industrial environments (e.g., extended temperature range, conformal coating), but also solutions that ensure high availability, such as redundancy. According to Siemens, SIMATIC PCS neo supports redundancy on multiple levels.

  • Controller redundancy: High availability (HA) controllers are configured in a redundant set-up to allow bumpless transfer should a controller fail.
  • HMI redundancy: The monitoring and control servers are redundant with each other, so clients such as operator stations continue to operate seamlessly, even if one server goes offline for any reason.
  • Control network redundancy: Redundant media solutions are available for Profinet or Profibus.

Process plants that run for 20 to 30 years require a DCS with the stability to not only stay running that long, but also to remain secure to both existing and future threats.


A DCS that runs a plant for many years must keep up with the times. Process plants may be expanded many times over the course of their lifecycles for a variety of reasons. The owner/operator may need to increase output to meet growing demand by adding new production capacity or may procure new equipment to produce new products. Existing equipment may also be upgraded over time to take advantage of new process technologies. To support these expansions, the DCS must be expandable by adding more control loops and new IO – often while the system is still running.


One control system that scales up or down to fit any application demand is clearly a benefit for equipment makers and owner/operators alike. From very small but highly available systems to installations with more than 100,000 IO channels, a DCS must be able to scale to the needs of each application. SIMATIC PCS neo was designed to scale from small units to large plant systems – upwards of 64,000 control loops are said to be possible based on exhaustive validation testing, according to Siemens.

Support for MTP

Module Type Package (MTP) standardizes equipment data models and interfaces to simplify equipment interoperability, allowing process equipment to be designed and built as modules (package units) that can be easily integrated with other modules to quickly add functionality or increase capacity. The MTP philosophy is that if all equipment in a process facility is modularized, it will be easy to upgrade or replace any piece of equipment at any time.

Modules or package units with their own automation are integrated with others via a process orchestration layer (POL), whose functionality is defined by VDI/VDE/NAMUR 2658 and IEC 63280.

According to Siemens, adding a module to an existing process is as simple as getting the appropriate MTP file from the equipment provider, and importing it into SIMATIC PCS neo. After that, all motors, valves, indicators and displays are immediately available for configuration.


Owner/operators agree: Simulating complex processes in software results in enormous savings in time and money. Using a digital Distributed Control Systemstwin during process design creates untold opportunities to optimize all phases of capital projects: from process layout to equipment selection to application testing. Simulation lets users validate system changes before they make it to the production system. New control logic such as interlocks or new parameters can be tested in a simulation environment to validate the changes before letting them run in the plant.

SIMATIC PCS neo integrates with Siemens’ SIMIT Simulation Platform to test process automation applications before deploying them in the plant, helping to reduce commissioning time later. Simulation tools also help users to optimize processes, resulting in greater efficiency throughout a process plant’s lifecycle. Finally, simulation software creates a realistic environment to train operators, helping them familiarize themselves with a system’s operation before going live.


Digitalization means not just collecting and evaluating process data, but also sharing these data with other software and hardware systems, while keeping plant documentation up to date. But simply being “open” isn’t enough. A modern DCS must offer tools to share data, all protected by bulletproof cybersecurity measures. According to Siemens, SIMATIC PCS neo supports these key aspects of integration:

  • Up-to-date plant documentation. Detailed version tracking of projects makes it easy to see who made edits, at what time, and on which objects. In addition, SIMATIC PCS neo integrates with Plant Automation Accelerator, which serves as a digital bridge in the detailed engineering phase between planning and the distributed control system.
  • Evaluate plant performance and optimize for higher output with the same equipment. Use HMI tools and libraries to monitor plant performance with Advance Performance Graphics, then use cloud-based AI to make recommendations for optimization.


DCS systems are installed for the long run. That means that thousands of process plants around the world are running systems installed 20 years ago or more. Besides the problem of obtaining spare parts for legacy hardware, these DCS systems simply were not built for the age of digitalization. They may be closed systems connected by proprietary networks that may be exposed to Distributed Control Systemscybersecurity threats that were unknown years ago.

The decision to migrate a distributed control system is not an easy one. Benefits must be weighed against disadvantages and cost, but the older the system, the longer the list of benefits tends to be.

Siemens claims that 25,000 plants worldwide are currently running SIMATIC. When Siemens first introduced SIMATIC PCS neo, it committed to continue support for SIMATIC PCS 7 in parallel, leaving the choice of system entirely to the user. One big difference to other suppliers: SIMATIC PCS neo runs on the same hardware, which means that a migration is possible while leaving most legacy hardware in place.

For owners/operators, the need to upgrade an existing distributed control system or to migrate to a whole new system might occur once in a generation. The arguments start making sense when an installed system has become too restrictive and inflexible, too maintenance-intensive, or no longer helps a plant meet its business goals. “Rip and replace” may sound like the easiest solution, but few plants can afford the downtime associated with a complete swap-out of hardware and software, not to mention the steep investment in training operators on a new system. Then there are the costs and the risk of integrating legacy enterprise software with a new control system.


A distributed control system must not only satisfy the requirements of current daily operations; it must also be ready to handle upgrades and expansions to meet future requirements. This stipulates a certain degree of system robustness in terms of both ruggedness and future-proofness. In addition to the ability to grow with the plant, a DCS must be ready to integrate and exchange data with future systems, and to accept protections against future cyber threats.

Siemens developed SIMATIC PCS neo with these goals specifically in mind. With a large installed base of distributed controls systems, SIMATIC PCS neo is designed to be scalable from small units to large plant installations, in new greenfield plants or as an upgrade to existing brownfields. The result is a fresh approach to the old science of distributed control based on principles of openness and collaboration – just what the next generation ordered.


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Keywords: Siemens, PCS neo, Distributed Control System, Operator Empowerment, Collaboration Engineering, System Robustness, ARC Advisory Group.


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