IO-Link Technology Solutions

What is IO-Link?

IO-Link is a standardised point-to-point connection between a sensor or actuator and an IO-Link master, standardised as IEC 61131-9 (SDCI). Unlike a classic switching output, IO-Link transmits not just an on/off signal but measurements, parameters and diagnostic data in both directions. The connection runs over an unshielded standard cable with M12 connector up to 20 metres long. Every device comes with a description file, the IODD, which specifies the data and parameters it offers.

How IO-Link is used in the IIoT

IO-Link is the simplest way to access data from the lowest field level. A pressure sensor no longer delivers just a threshold signal but the pressure in bar, its temperature and its operating state. IO-Link masters with an IoT interface, for example from ifm, Balluff, Turck or Murrelektronik, pass this data via MQTT, OPC UA or REST API directly to IT, in parallel to the controller. This enables condition monitoring, energy and process data acquisition without touching the PLC program. Parameterisation and automatic device replacement also shorten changeover and downtime.

IO-Link or fieldbus?

IO-Link does not replace a fieldbus; it extends it downwards. The master itself sits on Profinet, EtherNet/IP or EtherCAT and passes its sensors' data to the controller. Compared with analogue 4-20 mA signals, IO-Link saves analogue cards, is immune to interference and additionally delivers diagnostics. For wireless applications, for example on rotary tables or tool changers, there is IO-Link Wireless.

How an IO-Link system is structured

Each IO-Link sensor or actuator connects to its own port on the master; there is no bus wiring. The master sits as an IP67 module directly on the machine or as an IP20 module in the control cabinet and is connected to the controller via fieldbus. Many masters also have a second interface through which they send process and diagnostic data to an IoT platform. When a sensor is replaced, the master stores its parameters and transfers them automatically to the new device, so no new setup is required.

What to consider when choosing

For the master, consider port count, ingress protection (IP67 in the field or IP20 in the cabinet), fieldbus connection and whether it has a second, IT-side interface for MQTT or OPC UA. Port Class B provides a separate auxiliary supply that many actuators such as valve terminals require. For sensors, check the IODD to see which process and diagnostic data are actually available. For commissioning during operation, tools such as a USB IO-Link master on a laptop help.