Self-forming, self-healing wireless mesh networks for process instrumentation, now a mainstream alternative to wiring for monitoring-class measurement points.
IO-Link & IO-Link Wireless
A standardised point-to-point link that gives ordinary sensors and actuators digital parameters, identification and diagnostics. With around 71 million nodes installed it is mainstream in machine automation; its growth edges are process-adjacent equipment, wireless and safety.
What IO-Link is, and is not
IO-Link, standardised as IEC 61131-9, is not a fieldbus. It is a point-to-point connection between one device and one port on an IO-Link master, over the same unshielded three-wire cable used for standard switching sensors, up to 20 m long. The master connects upward to PROFINET, EtherNet/IP, EtherCAT or another network. Each device is described by an IODD file that tells the engineering tool what process data, parameters and events it offers.
Because the link is digital, a device can report a measured value and its status at the same time, be reconfigured remotely, and raise events such as a dirty lens or an over-temperature warning. The master's parameter server stores each device's settings and writes them into a like-for-like replacement automatically, which is often the feature maintenance teams value most.
Two extensions widen the scope. IO-Link Safety (IEC 61139-2) carries safety-related data for devices such as light curtains and emergency-stop buttons. IO-Link Wireless (IEC 61139-3, published by the IEC in November 2023) applies the same model over a 2.4 GHz radio for rotary tables, tool changers and other moving equipment 2.
| Conventional discrete/analogue | IO-Link | Ethernet-APL | |
|---|---|---|---|
| Cable | Standard sensor cable | Same unshielded 3-wire cable | Single twisted pair |
| Distance to the I/O point | Depends on signal type | Up to 20 m to the master | Up to 200 m spur, 1,000 m trunk |
| Digital parameters and diagnostics | No | Yes | Yes |
| Typical setting | Everywhere | Machines, skids, packaging lines | Process units, hazardous areas |
How big it has become
PI, the organisation behind PROFIBUS, PROFINET and IO-Link, reported in April 2026 that about 71 million IO-Link nodes are installed worldwide, with roughly 9.7 million new devices and master ports added in 2025. It also said the market is levelling off at a high level after several years of unusually strong volumes 1. These figures come from member companies' reports rather than an independent audit, but the scale is consistent with IO-Link's position as a default option in machine building.
Where it fits in a process plant
Inside a process plant IO-Link usually lives in packaged equipment rather than on the main instrument index: packaging and filling lines, water-treatment skids, compressors, utility systems and valve terminals on batch units. The 20 m limit and the small number of devices certified for hazardous areas keep it out of most classified process areas, where Ethernet-APL, HART and wireless instruments compete instead.
That matters for owners because IO-Link data inside packaged equipment is often invisible to the plant's main systems. The skid builder configures it, the device diagnostics stop at the skid PLC, and the parameter-server function may not even be enabled. Specifying how IO-Link data and diagnostics are passed up to plant systems costs little at purchase-order stage and a great deal later.
Practical points for owners
- Ask skid and machine suppliers to state where IO-Link is used, and to hand over IODD files and master configurations with the documentation.
- Make sure the parameter server is enabled and tested; otherwise device replacement is not plug-and-play.
- Standardise masters and port types (Class A and Class B ports differ in auxiliary power) to keep spares simple.
- Include IO-Link masters in the OT asset inventory. They are networked devices with firmware.
Evidence timeline
- 2018IO-Link Wireless system extensions, version 1.1, released by the IO-Link Community. 2
- Nov 2023IEC publishes IO-Link Wireless as IEC 61139-3:2023; base protocol (IEC 61131-9) and IO-Link Safety (IEC 61139-2) already standardised. 2
- Apr 2026PI reports about 71 million IO-Link nodes installed and 9.7 million added in 2025. 1
Why it sits at the Proven in Use stage
We have moved IO-Link from the Industry Acceptance stage to the Proven in Use stage in this edition. With tens of millions of installed nodes, a broad supplier base and IEC standards covering the base protocol, safety and wireless, the core technology is mainstream.
The previous placement reflected the less mature wireless variant. We now treat IO-Link Wireless and IO-Link Safety as growth edges of a mature technology rather than a reason to hold the whole entry back.
Adoption signals to watch
- Uptake of IO-Link Wireless beyond pilot installations.
- Wider ranges of IO-Link devices with hazardous-area approvals.
- Plant asset-management systems reading IO-Link diagnostics as routinely as HART.
Questions to ask before committing
- Does the layout keep every device within 20 m of an IO-Link master?
- Are IO-Link devices available with the area classification and ingress-protection ratings this location needs?
- Will the parameter server be enabled and tested so that device replacement really is plug-and-play?
- How will IO-Link diagnostics inside packaged equipment reach the plant's maintenance systems?
Terms used on this page
- IO-Link master
- The gateway that connects several IO-Link devices to a higher-level network.
- IODD
- IO Device Description, the file that describes a device's data and parameters.
- Parameter server
- The master function that stores device settings and restores them after a device swap.
Sources
- IO-Link continues growth in automation
- IO-Link Wireless designated as IEC 61139-3 standard
- IO-Link Wireless is now an international IEC standard
Related technologies
See this entry on the full maturity map · All Instrumentation entries · How placements are made. Stage and time-horizon placements are editorial judgements based on the public sources listed above, as of October 2026. They are not engineering, safety or investment advice; see the Terms of Use.