IIoT and PLC: Coexistence, Not Confrontation

By European Editors

Contributed By Digi-Key's European Editors

The Industrial Internet of Things promises to redesign machinery, reorganize processes, and harness the power of big data to improve productivity and profitability. According to some, familiar architectures and devices like programmable logic controllers (PLCs) could be swept away. An alternative view is that the explosion in data collection will drive a move towards even larger numbers of smaller devices like micro or nano PLCs that can be deployed almost anywhere throughout the factory.

Big data; new idea?

The Industrial Internet of Things is predicated on collecting large amounts of data from processes and equipment for intensive analysis in the Cloud. The objective is to enhance the re-optimization and reorganization of processes, pursuing improvements such as reduced waste and faster response to customer demands. Factories of the fourth industrial revolution (Industry 4.0) will likely contain many thousands of sensors throughout equipment and working areas, reporting on aspects as diverse as motor currents and vibrations, ambient temperature and humidity, final product test and inspection measurements, serial numbers, batch numbers, and timestamps.

The success of Industry 4.0 requires these thousands of channels of data to be efficiently collected into the Cloud to be stored, prioritized, grouped and analyzed, and ultimately transformed into improved instructions to be communicated to machines, and information to drive smart business decisions. The design of machinery, control systems, and factory communication networks is expected to change significantly, which could pose a threat to incumbent devices such as programmable logic controllers (PLCs) that have hitherto dominated data collection, processing and control tasks in conventional automation.

The desire to collect more data to improve manufacturing yield and assist business decision making did not originate with Industry 4.0. Enterprises have been looking to collect increasing quantities of data from equipment and automate exchanges between factory floor and back office analytical systems since long before the Cloud. The Industrial PC (IPC) is one example of a concept that emerged to enable PC-based automation with the benefits of a seamless data flow to and from decision makers on the corporate LAN. The PLC, however, retains several advantages including long lifecycles and high reliability, and has also evolved to meet market needs by increasing processing capability, providing extra functionality, and incorporating PC-based standards.


The proliferation of sensors and other data-gathering activities throughout the factories of the next industrial era could potentially overwhelm the capabilities of current PLCs. Some suggest that sensor data will be collected directly into the Cloud using a lightweight protocol such as MQTT (Message Queuing Telemetry Transport). A major advantage for today’s data-rich manufacturing environment is that MQTT can bypass large quantities of unchanging data, which can clog networks when using conventional poll/response protocols. MQTT’s publish/subscribe model allows smart sensors to publish only new data for the devices configured to receive it. Some important consumer IoT and social platforms are known to be taking advantage of the protocol’s low bandwidth demands, low latency and low power consumption. MQTT is well suited to use in control systems, and MQTT modules could provide a route for sending IIoT data directly to the Cloud. This offers a practicable means of handling the data generated by the large numbers of sensors distributed throughout the connected factory.


Alternatively, the conventional centralized PLC could be replaced by multiple smaller PLCs that are placed closer to the sensors they are monitoring and the mechanisms they are controlling. Micro or nano PLCs designed to communicate as part of the IIoT are emerging to fulfill this type of role, providing I/O channels in a small footprint with modular expansion options.

Crouzet is catering to this opportunity with its em4 family of nano PLCs such as the em4 Ethernet. The em4 measures 124.6 x 90 mm, and provides a selection of analog and digital IO and relay outputs. Digital and analog I/O expansion modules are also available, giving flexibility to cater to large or small installations. It can be programmed or debugged from anywhere on the local network, and can be connected to the internet on demand with no additional modules (Figure 1). As a convenient means of collecting data from sensors, the em4 can send simple scheduled datalogs by email or FTP, or send email alerts under the control of the application program. It can communicate with up to sixteen other devices on the network, and automatically detect up to eight connected em4 units. An 18 x 4 monochrome display and 6 button keypad provide the option to manage the PLC directly from its front panel.

Diagram of em4 Ethernet nano PLC

Figure 1: The em4 Ethernet nano PLC connects easily to other equipment on the LAN or the Internet.

Panasonic has a space-efficient ultra-compact PLC suitable for distributed monitoring and control, or for equipment miniaturization. The FP0R series is 90 mm high and 25 mm wide, and provides I/O including pulse outputs that allow multi-axis motor control. Up to three expansion modules can be added. Built-in FeRAM provides automatic batteryless data backup, allowing the equipment to be powered down without losing data. The PLC can share information with up to sixteen similar devices via a PLC-Link connected to an Ethernet network via an FP Web Server 2 module. Other features for motor control include counters and PWM outputs. Connectable CC_LINK and IO/LINK modules using popular protocols give extra flexibility for networking and sensor monitoring. The Crouzet em4 and Panasonic FPOR are programmed using the manufacturer’s standard programming software.

Maxim Integrated set out to provide more performance within a much smaller volume than the traditional PLC with its Micro PLC platform (Figure 2). Micro PLC digital and analog IO modules such as the MAXREFDES60 0 - 10 volt analog output module fits into a space about the size of a credit card. This form factor enables developers to achieve connectivity comparable to a standard PLC in about 10% of the space at half the power. Other Micro PLC modules are available, including a 4-channel analog input module, 8-channel digital input and output modules, and an RS-485 communications card. All come with example C source code and test data to help accelerate the implementation of next generation compact PLCs ready for Industry 4.0.

Image of Maxim Integrated Micro PLC compact modular platform

Figure 2: The Maxim Integrated Micro PLC is a compact modular platform that allows the user to select from a range of credit-card sized I/O boards.


PLCs have evolved throughout the history of industrial automation to provide a dependable and rugged means of monitoring and controlling processes and equipment. By adapting to market demands and emerging connectivity and communication standards, the PLC continues to be widely used by industrial equipment and factory designers. The latest micro and nano form factors should secure the PLC’s position in the IIoT and at the heart of Industry 4.0.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

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