What IEC 61499 means for the PLC

The IEC 61499 international standard doesn’t signal the end for the programmable logic controller (PLC), but its impact, particularly in process control applications, will change how PLCs are used.

By Martyn Hilbers August 10, 2021


Learning Objectives

  • IEC 61499 Function Block standard make it easier to use distributed with field devices on multiple, diverse hardware platforms.
  • Function blocks can change process control and improve operational readiness.
  • Advantages of integrating IT into OT include data analytics, IoT architectures.

IEC 61499 Function Block standard make it easier to use control platforms consisting of distributed autonomous IEC 61499-enabled field devices on multiple, diverse hardware platforms. Why is that important?

PLC history and progress for industrial use

It’s been a while since the programmable logic controller (PLC) was introduced. To be exact, it was 53 years ago when the Modular Digital Controller (Modicon) started to replace relay-based and pneumatic control systems. At that time, knowledge doubled at a rate of 14 years and the world has seen many changes since. First, human walked on the moon (1969), personal computing (1981), the internet (1991), the smartphone (around 2007). In spite of all these changes, engineers are still using and programming PLCs and distributed control systems (DCSs) in almost the same way as 1968.

This raises several questions around why this has barely changed since 1968. Are the PLC/DCS solutions that good? Is the industrial control community too conservative to change? Does the market not offer a better alternative? The answer is all of the above.

Factories have a lot to lose by being an early adopter of new control technologies, after all, who would want to be the first to commercially fly in an innovative airplane? It seems that an obvious risk averse business model combined with “we have always done it this way” mentality, makes the industrial control field a difficult market to break into for innovations.

How function blocks can change process control

The advent of IEC 61499 Function Blocks as a standard has had some engineers wondering if this is the beginning of the end of the PLC era? In the short term: No. In the long term: most definitely yes for process control applications. Here’s why.

The 20th century automation was characterized by measuring a limited amount of process values and using these values on a single computing platform to manipulate field equipment. The second quarter of the 21st century will be characterized by automation that analyzes large volumes of information (that is likely not process-related) to provide predictive analytics to optimize the underlying 20th century automation layer and to enable new levels of automation. I could have used the word data in the previous sentence but deliberately used the word information for the following reason.

The analogy of information technology (IT) and operational technology (OT) being like cats and dogs is likely going to strike a chord.

Data analytics, operational readiness

During the first quarter of the 21st century we are discovering the value of data analytics in a process control environment. To make use of data analytics, we have introduced IT in an OT environment. Two worlds that previously peacefully existed in their own space using the same technology with opposite security/user/access objectives are now forced to coexist with contradicting objectives in a shared environment.

How is IEC 61499 standard going to change the above and make PLCs obsolete? The IEC 61499 standard advocates the creation of standardized tested software modules for specific control functionalities. This allows for process control schemes to be composed from tested functionalities/software modules. So far there is nothing too new about this. It’s very much in line with current programming practices for PLCs and DCS platforms. With the IEC 61499 standard, the purpose of instantiating tested software modules is not only to create process control more effectively, but also with a higher level of operational readiness (low/no code solution by linking functionalities to one another and to field signals).

IEC 61499 aims for these functionalities to run distributed on multiple, various and smaller hardware platforms. Current variable frequency drives (VFDs) are already equipped with a small number of input/output (I/O) channels, can execute proportional-integral-derivative (PID) control loops in addition to custom logic functionality and communicate via Ethernet to PLC and DCS platforms. Creating true distributed control systems provided by interconnected autonomous field devices is closer than we might realize.

Autonomous field devices, Internet of things, manufacturing IT

So far, we have considered OT by means of distributed control functionalities provided by autonomous field devices. Now, let’s add IT to this and introduce the Internet of Things (IoT) at a device level. IoT at a field device level enables data driven 21st century automation (predictive data analytics) in an on premise or cloud environment.

This brings us back to the “cats and dogs” situation, how to bring a highly cyber secure, user profile specific, managed IT environment into an OT process environment that relies on unrestricted connectivity and access.

Nowadays, DCS and PLC platforms use Ethernet to communicate with remote I/O stations etc.  The Ethernet medium used is predominately copper or fiber (sometimes wireless) and have data speeds of 10Mbit/second and over. As an analog input/output (I/O) signal is commonly 16 bits and a digital input/output signal is only 1 bit, the utilization of this network is very low leaving a large bandwidth unused (comparable to a couple of drops of water in an empty bucket).

Advantages of integrating IT into OT

There are several products and solutions that have integrated an IT environment into an OT environment with various levels of success and practical usability. Among implementations of this is the Modicon M340 and M580 EPAC (Ethernet process automation controller). Like most PLC/PAC platforms, the M340/M580 uses Ethernet to communicate with remote I/O stations and uses the excess bandwidth for IoT purposes.

By combining the time-sensitive network (TSN) Protocol (an IEC 61850 derivative) with VLAN, Firewalling, etc., an IoT data channel and a deterministic OT data channel is created on the same physical cable completely cyber secure and segregated from one another. The solution serves IT and OT objectives in one environment and is very user-friendly. It is reasonable to expect that these types of IT/OT integrated solutions will become prevalent in field devices.

The IEC 61499 standard will reduce programming of control software to linking standardized/tested functionalities that run in cyber secure interconnected IoT enabled field devices that together provide distributed plant wide process control functionality. Where does this leave the trusted PLC? From here to nowhere.

This will not happen overnight and will require a transition period where most likely hybrid solutions consisting of PLCs and autonomous field devices will slowly make way for control platforms consisting of distributed autonomous IEC61499 enabled field devices. This transition has already started. Solutions currently available can be considered the first step in such a transition, and experts can assist in creating a roadmap for the IEC 61499 journey.

Martyn Hilbers is principal engineer, PLC-Easy.com. Edited by Chris Vavra, web content manager, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com.


Keywords: PLCs, IEC 61499, function blocks


By designing or adapting function blocks once and distributed to the control platform needed, how much time would you save?

Author Bio: Martyn Hilbers, PLC-Easy