Pepperl+Fuchs Blog

The Future Belongs to IO-Link: An Introduction

Posted by John Appleson on Tue, Jun 04, 2013

Welcome to the year 2023. Maybe there aren’t any flying cars and futuristic sci-fi cityscapes as foretold in the past, but there are other significant technological advancements. The smartphones of a decade ago have been replaced by far advanced technology that is worn like eyewear or clothing. Holographic conferences are more common as the new forum of face-to-face business meetings. Augmented reality has merged the virtual realm with the real world. And industry has turned from the older conventional sensing technology to IO-Link.

IO-Link open communication technology

Rewind to today. The last advancement isn’t far-fetched and is actually happening right now in 2013. The world of automation is already opening to the many benefits of IO-Link. Others have not heard of IO-Link or have just a vague understanding of it. If you are in the latter groups, this blog entry is for you. It’s the first in a series to explore IO-Link, IO-Link sensors, and why they matter to your industrial application.

IO-Link offers huge improvements in the configuration, control, and diagnostic capabilities of sensors. It minimizes the time and cost of project implementation, changeover, diagnostics, and downtime. It is simple, flexible, and a secure open communication technology. Some use IO-Link to tap into a large number of extra features and control elements not available with standard sensors, some use it for the diagnostic and tracking capabilities, some for enhanced control, and some for other reasons. Before getting into the advantages, it helps to understand the basics of IO-Link first.

IO-Link: The Basics

IO-Link was developed by a consortium of industrial manufacturing companies, including Pepperl+Fuchs, to offer a greatly improved alternative to standard input/output (SIO) sensors and actuators. IO-Link is an open protocol and is not restricted to one company, which makes it a very secure and widely accessible technology. The website of the IO-Link consortium is

IO-Link is a communication interface designed for devices like sensors and actuators. It is a point-to-point topology, not to be confused with a bus topology. Point-to-point is a connection method in which each sensor or actuator is connected to an IO-Link master port. An IO-Link master can have one or multiple ports. (See Figure 1 and note SDCI means single-drop digital communication interface.) By contrast, a bus system is where each sensor, actuator, and master is connected to one cable. The IO-Link master, in turn, can act as a gateway to a fieldbus such as EtherNet/ IP.

IO-Link is a communication interface with a point-to-point structureFigure 1. Point-to-point structure of IO-Link

IO-Link allows the transfer of three different types of information:

  1. Process data (PD) is the input or output information sent cyclically in a specific manner after the master is activated. It contains 1 to 32 bits and is usually sent every 2-3 ms. This data is also called cyclic data. Examples of process data include a single bit to indicate if an object is detected.
  2. Service data (SD) indicates different parameters or states of the sensor, but it is only sent on request by the IO-Link master. It can be much larger than the process data and can contain much more advanced information. This data is also called acyclic data. An example of service data is the serial number of a sensor. Both PD and SD can be sent in one telegram or in several telegrams.
  3. Event data indicates unusual occurrences that are important enough to be reported when they happen. An example of an event is a temperature overload that occurs when a sensor is exposed to temperatures beyond its specified limit.

An IO-Link product can always be identified by the IO-Link symbol, the double arrowhead depicted in Figure 2.

The IO-Link symbolFigure 2. IO-Link symbol

A significant advantage of IO-Link over older protocols is that IO-Link sensors can be used with IO-Link or as a standard I/O device. This is a huge advantage over other defined protocol sensors that can be used only with that protocol. So an IO-Link sensor can be dropped into an IO-Link system and start transferring its process data, service data, and event data. Or it can be used as a standard device which has a discrete transistor output on the typical pin position. This backwards compatibility makes IO-Link sensors versatile enough that a user can take advantage of IO-Link when necessary, but still revert back to a standard output transistor.

IO-Link sensors use the most standard industrial connector of any sensor, the 3-pin M12 (micro style) connector. No special cordsets are required to use an IO-Link sensor. As is the case with standard I/O sensors, Pins 1 and 3 are connected to the positive and negative terminals of the supply voltage, and pin 4 doubles as either the NPN or PNP discrete transistor output in standard input/output (SIO) mode or where the IO-Link communication occurs. See Figure 3.

M12 pin configuration of an IO-Link sensorFigure 3. M12 pin configuration of an IO-Link sensor

When an IO-Link sensor is powered, it always starts in SIO mode. If the sensor is connected to an IO-Link master and if the port on that master is configured to communication mode rather than SIO mode, then the master searches for the connected IO-Link sensor and initiates a process called wake-up. If the master ends communication to the sensor, the sensor reverts to SIO mode, which is called fall back.

Some information in this blog entry is credited to the IO-Link consortium’s IO-Link system overview (

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Topics: Terminology, Photoelectric Sensors

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