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How IO-Link Put The ‘Smart’ In Smart Factory

By Brian Condell and Michael Jackson

IO-Link® has the potential to make almost any factory sensor or actuator “smart”, allowing it to communicate and share valuable data with a process controller. This blog looks at the reasons why it was developed, how it works, where it can be used, and its limitations. See the previous blog post here.

Why was IO-Link Developed?

Historically every Fieldbus (e.g., MODBUS, Profibus) had its own connectors to connect a sensor or an actuator to a supported protocol meaning automation engineers had to understand the details about how it worked and to select the correct cables and input cards. To address these issues, manufacturers designed Fieldbus interface into their equipment but as the size of sensors and actuators shrunk, this approach became impractical. Apart from becoming smaller, manufacturing processes also required sensors that could transmit readings for physical quantities like temperature and pressure and which could be configured remotely by a process controller (bidirectional communication).  These were the main drivers behind the development of IO-Link as a global standardized interface that could work in the smallest devices produced by all equipment manufacturers. These devices could then be easily integrated into any network (Fieldbus or Industrial Ethernet) using an IO-Link *master. IO-Link sensors are required to be backward compatible with legacy binary sensors to make it easier to integrate into existing factory systems.

How Does IO-Link Work?

An IO-Link system consists of a device (a sensor or actuator) and an IO-Link master. See Figure 1. While each device can be connected to only one IO-Link master, an IO-Link master can service multiple devices.

Figure 1- IO-Link System

The IO-Link master acts as a gateway, bridging the link between connected devices and the upstream industrial network used by a process controller (Figure 2).


Figure 2 – How IO-Link fits into factory automation architecture


IO-Link is a serial digital point-to-point protocol where every device is connected to one physical port on the IO-Link master. No complex addressing is required and it uses standardized connectors (typically M8 or M12) over unshielded three-wire cables making installation both simple and cheap.

An IO-Link master port can operate in the following four modes:

  • IO-Link: the port is used for bi-directional IO-Link communication.
  • DI: the port behaves like a digital input.
  • DQ: the port behaves like a digital output.
  • Deactivated: “Deactivated” mode can be used for unused port

IO-Link data communication can be either cyclic or acyclic.

  • Cyclic communication occurs during normal operation, the IO-Link master drives the transfer of Process Data.
  • Acyclic data is ‘on request’ and can contain configuration or maintenance information (service data). For example, the IO-Link master might send a new configuration to a device after it has been powered-up or request the device configuration right before power-down. Event data is also acyclic and occurs when something unexpected happens and is reported to the controller with three levels of severity – notifications, warnings, and errors.

Where Can IO-Link be Used?

IO-Link is ideal for factory automation applications including:

  • Automated assembly lines: To enable quick installation and swift changeover of production runs
  • Machine tools: Sensor parameter settings (temperature, pressure, airflow) to enable fast setup and make faulty sensors easier to identify and replace
  • Conveyor belts: Speed and stop points can be changed dynamically depending on the load
  • Personalized manufacturing/batch size of One: With the ease of remote configuration IO-Link brings the flexibility of personalized manufacturing
  • Hydraulics systems: Where reliable signal transmission, temperature, pressure, and level are key requirements IO-Link ticks all the boxes

What Are Its Limitations?

It is important to be aware that IO-Link is not designed to support every type of sensor or actuator. It can only transmit up to 32 bytes of process data per cycle, so it is unsuitable for transporting large volumes of data produced by devices like cameras or scanners used in industrial imaging equipment. A cycle time of about 2ms (typical) makes it sufficiently fast for most factory automation requirements but not for high-speed applications. Additionally, the cable that connects a device and the IO-Link master cannot exceed 20 meters.

How Can I ‘IO-Link enable’ My Sensor or Actuator?

Analog Devices provides IO-Link device and IO-Link master physical layer interfaces/transceivers (PHY).  Our 4-port/8-port IO-Link master and device transceivers both feature integrated step-down regulators and LDO with ±60V cable interface protection for rugged performance in harsh industrial environments.

Please visit the below pages for more information about our IO-Link solutions.

 *The use of the word "master" here is in relation to the trademarked product name associated with IO-Link and therefore we are allowing its use.

Find the next blog post here.