Small, fast and cheap PLC-solutions usually offer few engineering options and often do not provide convenient visualisation. In contrast, distributed control systems integrate a host of components such as controls, engineering tools, HMIs (human machine interfaces) and numerous peripheral devices and tools.
The segment between PLCs and the world of control systems – the hybrid market – is currently being targeted by both sides. PLC components are becoming more powerful and they can therefore also process more complex tasks. ‘Lite’ control systems are being introduced and they are increasingly being installed in small to medium-sized applications with less complex automation tasks.
For small and less complex automation tasks with often only few signals standalone PLCs have been and are still used, because until now process control systems have been too expensive for these tasks.
In the process industry many control tasks, eg compressors, centrifuges or steam generators, have been automated as PLC-based package units, leading to variety of different control systems and tools.
Diminishing Returns
The use of different PLCs brings serious disadvantages for the users: different tools increase the training budget and lead to more complexity, but without adding value. Particularly during maintenance, minor changes can cause considerable expenses, as cross-influences from different systems require manual adjusting.
The differences in visualisation and operation as well as the individual alarm concepts used by the various manufacturers can, in extreme cases, even affect the availability and safety of the application and the total plant negatively.
Additionally, the flexibility of the maintenance personnel is reduced because not all users can be familiar with all tools. Often older PLCs can only be maintained by a small number of specialists, many of whom are due to retire over the next few years.
Procuring and storing spare parts for many different systems and products cause additional work and expenses. All these reasons result in higher costs for servicing and maintaining the plants.
In contrast to PLCs, control systems are primarily based on analogue control loops with slow monitoring and control functions but less on fast positioning or switching operations.
The process is operated and monitored in the control room. The systems and plants generally run continuously and often have very high demands when it comes to availability. Consequently, implementing changes must be possible in online project configuration.
Additionally, repairing and changing of components while operating the plant is essential. Applications are often specifically configured for one project and the processes concerned and therefore require powerful and efficient engineering-tools with extensive integration possibilities.
Compact Alternative
Driven by technological developments in the last years, manufacturers of process automation technology are nowadays able to offer control systems with higher scalability as an alternative to PLCs in process-oriented applications. The advantages are obvious: efficient engineering, easy operating and maintaining as well as increased productivity due to intelligent diagnosis.
It is now possible for smaller automation solutions, which to date have been dominated by PLCs, to benefit from the advantages of process control engineering, particularly in the process industry. There are opportunities for use in many industries, including chemicals, petrochemicals, oil and gas, metalworking, cement production, glass production, etc.
