Understanding the IO-Link Open-Source Protocol for Industrial Device Communications
Key Highlights
- IO-Link uses standard unshielded cables to enable real-time data exchange between sensors, actuators and control systems, replacing simple on/off signals with detailed device performance and diagnostic information.
- The open-source protocol requires no proprietary hardware or licensing fees and integrates seamlessly with established fieldbus systems like Profinet, EtherNet/IP and EtherCAT.
- Bi-directional communication allows devices to report their health status and performance data, enabling remote diagnostics, configuration changes,and early warning signs of component failure without on-site visits.
Most of the history of industrial automation has been about big machines talking to other big machines. Over time, however, many automation devices have been getting smaller and smarter. For example, sensors and actuators are no longer limited to being told whether they should be on or off. They can talk back to the control system, function with greater precision, and provide real-time data about their health and performance.
Sending that much information back and forth between small devices and higher-level controllers would have required thick bundles of wiring or cost-prohibitive chipsets in the past. Today, however, system integrators and device manufacturers are exploring the use of IO-Link to overcome this issue with excessive cabling and costs.
IO-Link is an open-source communication protocol that enables two-way data transfer and advanced capabilities at relatively low cost over single-wire connections.
Although IO-Link has been around since 2006, its use has become much more widespread since 2020. This trend has been driven by the rapid growth of industrial Internet of Things (IIoT) devices and more integrated manufacturing facilities. Growing demand for remote configuration and predictive maintenance is also speeding the pace of adoption.
Another key factor in IO-Link’s success is that it augments, rather than replaces, familiar technologies.
What is IO-Link?
IO-Link is the first globally standardized protocol (IEC 61131-9) for point-to-point communication between sensors, actuators and control systems such as programmable logic controllers (PLCs) and human-machine interfaces (HMIs). It was developed by a consortium of automation companies and other industry stakeholders in response to the increasing complexity and miniaturization of devices, as well as the need for more detailed data than the binary signals typically sent in the past.
A single standard, unshielded wire enables fast, two-way communication with an IO-Link master hub, which enables integration with higher-level systems. Although most often used with Profinet, IO-Link also has specifications for integration with EtherNet/IP, EtherCAT and other major fieldbus systems. The primary limitation of IO-Link is distance. Packet loss can occur if a cable exceeds 20 meters or so. This is a minor concern, however, since electric sensors and actuators typically don’t require cables that long.
Common uses of the technology include factory automation, condition-based monitoring, asset management and quality control.
Plays nice with legacy equipment
Although greater efficiency and throughput are common goals of industrial automation, big disruptive changes aren’t always welcome. It’s a rare operation that’s willing to rip and replace an expensive system that’s getting the job done. Even greenfield facilities hesitate to become early adopters.
With IO-Link, a proximity switch or laser sensor can not only tell the controller that it’s detected an object, but how far away it is.
One of the great advantages of IO-Link is its ability to integrate seamlessly with established higher-level control systems. Individual wires from devices connect to IO-Link hubs, known as “masters”, via standard M5, M8 or M12 connectors. The master then communicates with the PLC using whatever fieldbus protocol you prefer.
Key benefits of IO-Link
- Lower cost and weight: IO-Link requires less wiring, minimal power and no software licensing fees. In addition, it allows point-to-point communication without requiring more expensive components like linear encoders. This makes it a lighter-weight technology that’s easier to justify incorporating into smaller and less-expensive devices. It also allows many more devices to be included in a sensor network than ever before by reducing the number of ports required to manage them.
- More robust communication: Instead of responding to simple binary instructions, sensors and actuators can now communicate data back and forth in real time, providing detailed device and process data, plus status and fault messages. For example, IO-Link compatible sensors can provide the PLC with specific position data, making them more capable and flexible.
- Flexibility of open-source technology: No proprietary hardware or software is required. Device configuration and performance can be customized or simplified with basic XML programming. A multi-vendor, centralized IO-Link database makes any end-user changes straightforward. Virtually any type of sensor or actuator can be built with IO-Link capability.
- Simplified installation and integration: IO-Link devices are practically plug-and-play. Individual devices may have unique setup needs depending on the manufacturer but typically work seamlessly and are easy to maintain once up and running. Following an initial IO-Link setup, the setup process for similar devices can be automated using parameter data from the end user’s server.
- Faster data: IO-Link offers three communication speeds: 4.8kBaud, 38.4kBaud and 230.4kBaud.
- Remote maintenance and monitoring capabilities: Bi-directional communication enables remote alerts and diagnostics for maintenance applications. Many troubleshooting issues that used to require on-site hardware adjustments can now be resolved via a secure internet connection. Integrators can also use device data to deliver real-time monitoring and predictive maintenance capabilities.
- Leverages existing infrastructure: The established international standard allows IO-Link devices to be integrated into any standard control system anywhere in the world.
- Proven technology: Global industry acceptance is widespread and many sensors and actuators sold today are IO-Link ready.
Wired and wireless IO-Link applications
Minimizing wiring is highly beneficial in itself. If you’re building a robotic arm, for example, every ounce of weight you can eliminate delivers performance advantages. It also gives you the flexibility to incorporate more devices (e.g., grippers) into end-of-arm tooling.
IO-Link was developed by a consortium of automation companies and other industry stakeholders in response to the increasing complexity and miniaturization of devices, as well as the need for more detailed data than the binary signals typically sent in the past.
Another benefit is the ability to get variable data from sensors. In the past, many small devices could only tell the system if they were on or off. Now it’s possible to track movements or distances down to a fraction of a millimeter. With IO-Link, a proximity switch or laser sensor can not only tell the controller that it’s detected an object, but how far away it is. Data like this can be used to make adjustments on a case-by-case basis. For example, the size or position of a box may determine whether a sortation system diverts it to another line or keeps it on the current conveyor path.
Movements outside a certain threshold can provide early warning signs of performance loss or component failure. This is one of the key drivers of predictive maintenance. Alert thresholds can be set by the integrator or, in some cases, the end user.
Eliminating wires is the obvious next frontier. The IO-Link Wireless standard is already making this possible. Up to three IO-Link wireless masters can operate in the same airspace, each supporting up to 40 wireless devices. This means that as many as 120 wireless devices can be controlled within a 20-by-20-meter production cell, using the same processing methodology as the wired version of IO-Link with minor programming changes.
Dr. Dave Sessoms is the senior lead engineer for Johnson Electric’s Warehouse Automation business unit.
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About the Author
Dr. Dave Sessoms
Dr. Dave Sessoms is the Senior Lead Engineer for the Warehouse Automation business unit. He specializes in developing technical solutions to optimize efficiency and solve complex customer challenges. With a strong background in innovation, he previously worked on developing conformal printed electronics for the biomedical and consumer electronics industries. He is passionate about automation and emerging technologies, bringing a deep technical expertise to the forefront of modern warehouse automation solutions. Dr. Sessoms holds a Ph.D. in physics from the University of Fribourg, Switzerland.
