Trends and innovations in the realm of control

 New control systems for the process industry are replacing traditional DCS systems 

Shai Gershon, Contel Group.

This article reviews trends and new developments in the realm of industrial control, with emphasis on process control systems used to operate and control batch and continuous manufacturing processes.

Background

For three decades, dedicated control systems from world-leading DCS manufacturers were extensively used in Israeli industry and in process industries worldwide. Most of the large process plants in Israel in the chemical and petrochemical sectors, as well as some of the leading pharmaceutical manufacturers use dedicated DCS systems for process control in their manufacturing facilities. The most widely used DCS systems in Israel and globally are Honeywell’s TDC, Emerson’ Delta-V, and Foxboro’s I/A system. DCS systems excel in hardware and software components designed and programmed in advance for commonly used control loops in the heavy process industry. Manufacturers can implement control systems for manufacturing processes by reusing hardware/software components built in advance for process control purposes. However, these systems are considered expert systems that require special knowledge and experience in order to develop and maintain them, and hence, the total cost of ownership is high compared to other control systems.

Alongside DCS systems, more widespread use is made of industrial control systems based on programmable logic controllers (PLCs) and local HMIs. PLCs and HMIs were previously used for control of processes not directly associated with the manufacturing process itself, but rather with the process support services (water supply, electricity, wastewater and conveyance systems, discrete machines, etc.).

Most of the large process plants in Israel that employ DCS systems simultaneously maintain and develop a range of control systems based on PLCs and local HMIs. The high cost of DCS hardware and shortage of engineers familiar with these systems led manufacturers to seek solutions that circumvent DCS, and gradually PLC systems trickled into secondary manufacturing processes as well, becoming more popular for implementation in process industries as well.

Comparison table: PLC versus DCS systems in the period 1980–2000

Trends and innovations over the past decade

With the evolution of control systems and their penetration of areas previously reserved primarily for DCS systems, the makers of PLCs continued to enhance and develop their hardware components and HMIs. Thanks to huge investments in R&D and incorporation of advanced technology and powerful processors, PLC controllers are considerably faster and possess over a 1000 times more memory than controllers installed just a decade or two ago. These technological innovations enabled traditional makers of controllers to launch a series of new control systems that integrate PLC with HMI, and to push back the old and unwieldy DCS systems. The key to success was the integration and synchronization of the HMI with the control system, and development of a single unified HMI-controller system.

Disruptive technology

The fate of DCS systems brings to mind the Theory of Disruptive Innovation proposed by Harvard Professor Clayton Christensen: a new technology is developed in little corners, almost in secret. At a certain point, the technology becomes noticed. It is at this juncture that the companies who control the current technology examine it. However, they have no reason to replace the existing technology due to the high cost of the change, or because the new technology is inferior, or only suited to a small market segment. The crux of the matter: the technology is too small to be attractive to the current technology giants, but too big to keep innovative companies afloat. And then something dramatic happens; a modification or an improvement, sometimes unexpected, that makes the new technology suited to a large portion of the market, and for the most part, also more preferable. Within a short time, the old king is deposed by the new one, and in our case, by process control based on a PLC-HMI integrated control system.

 One database

If, at the end of the first decade of the 21st century, industrial control personnel were obliged to maintain multiple databases, for both the PLCs and the HMI systems, subsequent technological innovations and R&D efforts enabled manufacturers of control systems to market a complete control system containing PLCs and HMIs sharing a single database. This breakthrough led to a significant reduction in the cost of developing and maintaining a PLC-based industrial control system. Previously, manufacturers had to configure each and every I/O point, both in the PLC and in the HMI, as well as in other ancillary systems (industrial panels, and data collection software). Now, with a shared, centralized database, all the configuring can be done in a single location.

Built-in object libraries

While DCS manufacturers excelled at process control and dedicated control loops supplied with the systems, PLC manufacturers improved these features and today supply a whole host of software and hardware objects ready out-of-the-box for use by developers. This paved the way for adapting PLC driven control systems to the process production floor. The main advantage of DCS was now also implemented in its younger brother, the PLC.

The key to success: deployment of a unified PLC-HMI process control system from a single manufacturer

In order to gain the major benefits of a PLC-driven control system in the process industry, control engineers would do well to deploy one control system from a single manufacturer that incorporates both PLC and HMI. In the past, process control engineers tended to separate the HMI from the PLCs and to select different manufacturers for each. Today, the integration of the two is essential to achieve the new power inherent in the technologies offered by the manufacturers.

Comparison table: PLC versus DCS systems – the situation today

Consequently, in recent years we witnessing a growing trend – more and more process plants in Israel and worldwide are coming to rely on unified PLC-HMI systems from a single manufacturer. With this winning combination and built-in object libraries, manufacturers achieve better performance than with the veteran DCS systems, plus significantly lower total cost of ownership.

About PlantPAx from Rockwell-Automation

Manufacturer Allen-Bradley, acquired two decades ago by Rockwell Automation, is one of the leading investors in R&D for process control. Over the past decade, the company has released versions of hardware and software that allow manufacturers to benefit from the fruits of its R&D, and to reduce the total cost of ownership. Its series of Factory Talk products enables developers to conduct development using a single database, both for the control systems and for the accompanying software. The PLC and integrated HMI are branded under the name PlantPAx, the all-in-one process control system fielded by Rockwell. The shared object libraries contain the controller software and the HMI operation screens for whole series of control devices.

Below is an example of a motor screen:

This built-in screen is used to operate a motor (pump, conveyor, mixer, etc.). The screen can be used to turn the motor on and off, reset faults, lock and change the motor status, change the name and description displayed, and also change the alerts and other features of the motor. In addition to that screen, there is also an interlock screen, start-up counter screen, startup protection screen and help screen.

Below is the built-in help screen that comes together with the motor screen:

All the symbols that appear in the motor screen are briefly explained in the help screen. The screen, like the other PlantPAx screens and objects, is editable, so that the language can easily be changed to Hebrew, Russian or Arabic, or to all the languages combined.

 One database

In a project at a detergent manufacturing plant executed in Israel several years ago, a PLC and HMI software were used based on the outmoded method of configuring two databases, one for the PLC and one for the HMI. Over 10,000 tags had to be defined in each database and synchronized between the two databases. The preparation of the tags in each database, and keeping them synchronized, consumed a considerable amount of time during the commissioning and maintenance period. In a more recent project, the commissioning of which was completed last year, the new technology was deployed, enabling the use of just one database, located in the controller. The entire HMI was written without the need for a single tag. The consolidation of the two databases into one saved a lot of time in the project preparations, and especially in operation on the ground. Equipment is added and details changed via the HMI screen, and are updated immediately in the PLC where the data are stored.