Scalability Adds Value Strong Growth in the Hybrid Control Market

Editor: Dr. Jörg Kempf

The advantages of process control technology can now be exploited in the small automation solutions market which has been dominated in the past by PLCs (programmable logic controllers).

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The AC 700F expands the downward scalability of the Freelance 800F control system to applications with only a few I/Os. (Pictures: ABB)
The AC 700F expands the downward scalability of the Freelance 800F control system to applications with only a few I/Os. (Pictures: ABB)
( Archiv: Vogel Business Media )

The magic word here is hybrid automation. Read this article to find out how ABB has succeeded in bridging the gap between simple controllers and fully-fledged process control systems. In today’s world, automation is an essential feature of any machine, process or system. The range of applications is very diverse, and there are enormous differences between the controllers and systems which are deployed to meet the different needs. The automation spectrum ranges from large-scale systems that control entire power stations or refineries down to small and very-small scale controllers at the machine level. Small, speedy programmable logic controllers (PLCs) have traditionally been the solution of choice for machine and field level applications, whereas large distributed control systems (DCS) have dominated the large solutions market.

However, the practical, cost-effective boundary between these two worlds is currently in a state of flux. New hybrid automation solutions are moving into the market space between PLCs and large control systems. This segment is currently being addressed from both ends. PLC manufacturers are attempting to add more powerful functions to their components. Control systems are being “streamlined” to make them suitable for less complex control applications. The ABB AC 700F controller bridges the gap between simple controllers and fully-fledged process control systems. It is part of the compact Freelance 800F control system, a product which is firmly established in the market (particularly in the process industry) and which offers all the features of a process control system. The AC 700F controller adds downward scalability to address smaller, simpler applications without forcing the user to make compromises in safety, operability or ease of use.


Small, fast, low-cost PLC automation solutions usually come at a price, namely reduced engineering efficiency and, in many cases, a lack of user-friendly visualization. In contrast, large process control systems offer a number of features including controllers, engineering tools, user interfaces and a range of other peripherals and tools. Stand-alone PLCs were often deployed in the past for small control applications involving only a few signals, because control systems were simply too expensive. Why use a sledgehammer to crack a nut? Many PLC-based packaged units have been designed for applications in the process industry such as compressors, centrifuges and steam generators, resulting in a large number of different control solutions.

Why not simply use a PLC?

Deployment of different PLCs has a number of disadvantages which become more serious as users attempt to increase efficiency at all levels.

  • Maintenance and repair effort rises dramatically as the number of different control systems increases. Spare parts procurement and storage drive costs up.
  • More training is needed to teach users how to handle the multiplicity of software programs and tools, and familiarization periods become longer.
  • Particularly during the design phase, a lot of engineering effort may be needed to introduce minor changes, because interdependency between different controllers has to be resolved manually.
  • In extreme cases, the multiplicity of visualization, operating and alarm strategies used by different manufacturers can have a negative impact on system availability and safety.
  • Often, there are few people left who still know how to maintain older PLCs.

All of these factors increase system maintenance and repair costs.

In contrast to PLCs, process control systems are generally used for non time critical analogue control loops rather than high-speed positioning and switching applications. Plant personnel operate and monitor the process to a large extent right from the central control station. The systems run continuously, and high availability is a critical issue. Design changes to the process control system have to be carried out online, and it must be possible to swap components during ongoing system operation. Applications are normally optimized for a specific process on a project basis, and that requires efficient engineering tools with a wealth of functions and extensive integration options.

Automation system manufacturers, leveraging advances in technology in recent years, are now able to offer compact, highly scalable process control solutions as an alternative to PLCs. The advantages are obvious: efficient engineering, simple operation and maintenance and intelligent diagnostics which enhance productivity. This is where the real strengths of the Freelance 800F control system and the AC 700F controller come into play. Over the years, users have come to appreciate the ease of operation and quick familiarization which this system offers.

Examples from real life

The solution has been on the market for over a year now, and many examples demonstrate how efficient it is.

Anti-surge control on turbo gas compressors

Air Liquide, Business Line Large Industries in Frankfurt, uses the AC 700F for anti-surge control on turbo gas compressors. Compressors are often the most critical and cost-intensive subsystems. Intelligent controllers are needed to prevent damage to or destruction of these valuable assets. Compressor operating conditions can become unstable and dangerous if the ratio between the differential pressure and the flow deviates too much from the nominal value. This may result in back-flow which is known as surging. The stress on the blades causes increased wear and component damage, and the whole system may come to a halt.

Compressors are often fitted with a surge control valve to prevent this from happening. For cost reasons, the amount of gas which is released should be kept to a minimum. If an optimized anti-surge control system is deployed, the compressor can be operated near the surge line. Improved partial-load performance increases component service life and enhances compressor efficiency.

Air Liquide was able to integrate the AC 700F controller into an existing Freelance 800F-System to create an optimized, cost-efficient control solution. Easy, seamless signal connectivity to the control system, simple migration of the logic to the controller and a very good price-performance ratio were the main reasons why the project management team decided to go with the Freelance 800F. “System editing is very user-friendly. The Freelance 800F has a big advantage in this respect compared to systems made by other manufacturers,” explained Michael Möller, Technical Support Large Industries at Air Liquide. He also mentioned that this solution saves time and money during commissioning.

Inverted filter centrifuge control system

Another example is an inverted filter centrifuge at AlzChem. An AC 700F controller, which was easily integrated into the existing Freelance 800F control system, has replaced the previous PLC solution. This has a number of advantages. Only one engineering tool is now needed to configure the entire system. Engineering is less complex, commissioning is far less time consuming and operation is less error prone.

Hartmut Rohner, Instrumentation and Control Manager at AlzChem, is particularly impressed with the simple, user-friendly handling features of the AC 700F controller. “It is easy for anyone to learn how to use the hardware and software. The standard program which was supplied by the centrifuge manufacturer was very hard to understand.”

In Rohner’s opinion, the AC 700F solution offers significant advantages during maintenance and troubleshooting. A programming device is needed to troubleshoot systems made by other manufacturers, but extensive failure analysis can be performed from the Freelance 800F console. “Simply by looking at the status, I know where the problem lies. That is not so easy on other systems.”

Natural gas pipelines

The AC 700F controller also has a proven track record in natural gas pipeline applications. Creos Deutschland operates 20 distributed pumping stations in the western region of Germany. Freelance 800F control systems, which can be operated either locally or from a remote control center, have been running problem-free at the stations for many years. AC 700F controllers have been installed at four of the smaller stations. Again in this case, the excellent price-performance ratio and ease of integration into the existing system were the deciding factors.


The Freelance 800F and AC 700F controller bring the advantages of large control system technology to the small automation solutions market which has been dominated in the past by PLCs. Similar to the proven AC 800F, the controller can be integrated into existing Freelance 800F systems. In contrast to PLC-based solutions, the AC 700F offers all the benefits of a compact control system.

A single engineering tool for all applications: Control Builder F features a simple, well-structured, intuitive DigiVis-based user interface, turnkey components such as faceplates, module diagnostics, event lists, alarm lines, trend graphs and automatically generated sequence displays. Pre-defined libraries and faceplates, which have a proven track record in field application, increase application transparency, readability and adaptability and enhance safety. Diagnostic features reduce cost and increase availability during ongoing operation and maintenance. The overall system is significantly more efficient.