The DCS spirit lives on everywhere

Classic distributed control systems typically remain only in high-availability refining and power applications, but their strategies and capabilities persist in descendants and today’s sophisticated networks.

3 of 3 1 | 2 | 3 > View on one page

Source: Saudi Aramco

Similarly, Invensys Process Systems just unveiled plans to renovate DCSs at Saudi Aramco’s Shedgum and ‘Uthmaniyah gas plants, which produce more than 4 billion standard cubic ft./day (scfd) to fuel local power plants and provide petrochemical feedstock. The company’s two largest gas plants have large I/A Series systems, which replaced analog panel board in the late late-1990s (See Figure 3), and will now be upgraded with Invensys’ I/A Series Mesh Control Network via its Address Translation Station (ATS). ATS provides a transparent bridge between I/A Series stations on older Nodebus process control networks and those residing on the mesh network.

“While the DCS industry as a whole has reached a degree of maturity, DCSs continue to evolve in some exciting and beneficial ways.  These include greater field integration capabilities, increased functional distribution, and better integration with other plant- and enterprise-level systems,” says Betty Naylor-McDevitt, Invensys’ systems marketing director. “We believe that Invensys accelerated this trend with the recent introduction of the InFusion enterprise control system (ECS), which, while not itself a DCS, provides a common engineering, application, and information environment across all plant-level systems (DCS, PLC, ESD, CMMS, MES, etc.) regardless of vendor. 

Honeywell’s Sweet adds that, “It costs a lot to put a sensor into a plant of you have to drill holes, run wires, and do individual configurations. People are realizing that wireless doesn’t just cost far less, but also allows them to put in many more sensors. This is like having a 10-bedroom house, and being able to have a thermostat in every room. For instance, though Honeywell recently announced a wireless version of Experion PKS, Sweet says it too will have to provide the same 24/7 availability and security that DCSs have always delivered. “We just have to figure out in the lab how to make sure a wireless DCS never drops a critical message, and make sure that no one can hack it,” adds Sweet. “Then we have to adapt these methods for use in the field and get people comfortable using them there, though it may take a couple of years.”     

In short, while the “d” in DCS changed from meaning “distributed” to “digital,” it now covers both at a level of intelligence and networking capability undreamed of when DCSs were invented. You can’t get much more distributed than making most of your process control decisions far out in the field itself.

“DCS evolution is continuing on the path toward an integrated, open, interoperable infrastructure on which traditional DCS companies add value through their knowledge, support, and expertise. The reason for the slow progress is this change requires modifying DCS business models. So, it’s the business model, not the technology that is ‘managing’ the transition to the next generation of open systems,” says Ian Verhappen, industrial networks director for MTL Instrument Group. “Once the hardware platform becomes based on industrial-grade, COTS technology with open standards, the added value of process knowledge/integration and long term support will be the differentiators and value adders. As hardware migrates to COTS, it also tends to become commoditized and a new category of supplier enters this area to concentrate on supplying the needs of the process control industry. For evidence of the open standards making this possible, you need look no further than the various communications organizations (Foundation fieldbus, Profibus, HART, OPC, etc.) and the ISA and IEC committees (ISA-50, 100, 99, 84 88, 95, 20, etc.).

“The second trend is that DCS's are becoming more truly distributed by migrating more of the control capability to the field/fringes. An example of this is the preponderance of remote I/O (RIO). However, the point where DCS systems stop from a price/performance ratio, has been traditionally where the PLC has been selected to fill the void,” adds Verhappen. “Unfortunately, the PLC's heritage is that of factory automation and discrete control (Analog and PID algorithms are 10-15 years old) and they therefore have the paradigm entirely different from the DCS paradigm. Some suppliers have therefore been building hybrid control products to fill this gap.”

In addition, DCSs also are useful for capturing the procedural expertise of soon-to or recently retired engineers. DCSs can formalize measurements, collected data based on them, and help provide consistent performance recommendations. “This means users don’t need to rely on tribal knowledge as much as they did in the past,” adds Sweet. “DCSs have evolved from using open-system technologies to working on PCs and onward to wireless. You can’t call them dinosaurs.”

3 of 3 1 | 2 | 3 > View on one page
Show Comments
Hide Comments

Join the discussion

We welcome your thoughtful comments.
All comments will display your user name.

Want to participate in the discussion?

Register for free

Log in for complete access.


No one has commented on this page yet.

RSS feed for comments on this page | RSS feed for all comments