In modern industrial automation, reliable, fast and efficient sensor communication is essential. As a pioneer for Industry 4.0 applications, IO-Link ensures seamless communication down to the lowest field level, thereby enabling easy integration of sensors and actuators into modern automation environments. In the following, we will explain the most important aspects of IO-Link and the associated advantages for industrial processes.
IO-Link is the first global standardized interface for fieldbus-independent communication between sensors/actuators and the control level of an automation system. The technology enables bidirectional data transmission and facilitates the diagnosis and parameterization of connected devices.
IO-Link communication always takes place between two end points, namely an IO-Link master and an IO-Link device (sensor/actuator). Data is transmitted between the master and the device via standardized and cost-effective 3- or 5-core cables. Digital data transmission eliminates the typical problems of analog transmission (signal loss, electromagnetic interference, inaccuracy, etc.). The IO-Link master is the link to a higher-level automation system or a control unit (PLC). Communication typically takes place via Industrial Ethernet (PROFINET, EtherNet/IP, Modbus TCP, etc.).
An IO-Link system always consists of several components. These include:
Typical IO-Link architecture
IO-Link devices (also known as IO devices) include sensors, actuators and RFID readers that communicate directly with an IO-Link master via the IO-Link protocol. Their major advantage is their ability to transmit process data as well as service and diagnostic data such as operating statuses or error messages.
The IO-Link master is a central component in an IO-Link system and serves as a link between IO-Link devices (field level) and a control unit (control level). It provides several IO-Link ports (typically 4 or 8) for connecting the devices, collects the data from the connected devices and forwards them in a bundle to the higher-level control unit. It supplies the devices with power, manages them and handles the configuration and diagnostics of the devices.
It also offers various error detection functions and facilitates integration into existing IT systems, which significantly increases efficiency and flexibility in automation solutions, especially in the context of Industry 4.0. Typically, a master has an integrated web server so that remote access is possible and all functions can be used directly over the network.
Automation pyramid with and without IO-Link
IO-Link Safety is an extension of the IO-Link technology that was developed specifically for safety-critical applications in industrial environments. It enables the integration of safety functions into the IO-Link architecture and extends the existing IO-Link standard to include safety-related communication between sensors or actuators and a safety controller.
Similar to IO-Link Safety, IO-Link Wireless is an extension of conventional IO-Link communication that enables sensors and actuators to be connected wirelessly to control systems. This means that IO-Link communication can be carried out wirelessly without physical cabling, thus improving installation, flexibility and scalability in industrial environments. IO-Link Wireless is often used for system components that are difficult to access or move, or for expensive and complicated installations.
The abbreviation IODD stands for IO Device Description. This is a file that describes the properties of an IO-Link device. It contains important information such as the device type, the manufacturer ID, the communication parameters and details about the device's functionality. IODDs enable the IO-Link master and the higher-level systems to automatically recognize the connected devices and configure them correctly.
The IEC 61131-9 standard is an international standard that has been specifically developed for communication between controllers and devices in industrial automation systems. It defines the technical specifications for “single-drop digital communication interfaces” (SDCI), which are generally known as IO-Link.
IO-Link architectures offer numerous benefits, ranging from the optimization of production processes to the reduction of maintenance costs:
Flexibility, production performance and remote maintenance are important performance parameters for machines and systems. With IO-Link sensors, the system operator now also has access to the lowest field level. With minimal effort, sensor information, configuration parameters and diagnostic data can be retrieved to optimally evaluate system conditions.
The use of IO-Link can significantly reduce the time and effort required for assembly and commissioning. This is possible due to simplified cabling and the option of automating commissioning by maintaining and duplicating parameters.
Pre-assembled cables are used during assembly, eliminating the need for self-assembly and avoiding sources of error. Commissioning can also be automated, since the parameters can be downloaded in a matter of seconds and are available in the device.
Due to the fieldbus independence, the variety of sensors in stock is considerably reduced and each sensor always has its “ID card” with it, so to speak, thanks to the IODD.
With modern IO-Link systems, unexpected plant shutdowns due to a sensor failure are a thing of the past. After all, the functions integrated in the sensors, such as operating hours counters, drag indicators, and error and short-circuit detection, help to identify and rectify critical sensor conditions in good time, significantly increasing plant efficiency.
IO-Link makes it possible to exchange both cyclic and acyclic data with higher-level systems. This means, for example, that parameter data can be loaded into a sensor during operation or diagnostic data can be read out. Thanks to a transmission speed of COM 3 at 230.4 kbaud and cycle times of less than 1 ms in some cases, data is exchanged quickly and is available in seconds.
The Device ID is a unique identifier assigned by the manufacturer for each IO-Link device. It enables the master to clearly identify the connected device and to assign the appropriate device description (IODD – IO Device Description). As soon as the IODD has been imported into the master, the master knows all the properties of the device. For a sensor, these properties can be, for example, the sensor type (temperature sensor, pressure sensor, etc.), measuring range or accuracy class. The IODD also contains various information about the device manufacturer, such as the manufacturer's name, the manufacturer's logo or the manufacturer's URL. When a sensor is connected to a master port, the device IDs are compared. If the device ID of the sensor does not match the IODD stored for this port, this is immediately recognized and an error message is displayed. This means that, for example, the swapping of a sensor with different measuring ranges or accuracy classes can be detected immediately. The “wrong” sensor can thus be replaced directly after installation and not only when the system is in operation, thus reducing downtime.
There are three different transmission speeds, which are designated COM1, COM2 and COM3:
Each IO-Link device can handle one of the three transmission rates and thus defines the communication speed for the respective port. An IO-Link master can handle all three transmission rates.
An IO-Link profile is a standardized collection of functions and parameters defined for specific device types or applications. These profiles simplify the integration and exchange of IO-Link devices because they use the same functions and data formats regardless of the manufacturer. The following profiles are currently available:
The Common Profile provides a basis for standardizing certain functions across different device types. It defines basic parameters and functions that are relevant for many IO-Link devices, regardless of their specific application. This facilitates the integration and management of devices from different manufacturers within an IO-Link system.
The Smart Sensor Profile is specifically designed for intelligent sensors and includes advanced features that go beyond the basic functions of a simple sensor. These may include, for example, extended diagnostic data, condition monitoring functions and the ability to self-configure. This profile enables sensors not only to collect data, but also to process and communicate information about their own condition and performance, which can be crucial for predictive maintenance.
The Firmware Update Profile defines a standardized process for updating the firmware of IO-Link devices via the IO-Link connection. This profile is particularly important as it enables the maintenance and update of devices in the field without the need for physical access or replacement of the devices. This means that updates can be carried out more quickly and cost-effectively.
The IO-Link community is already working on further profiles that will further increase the range of functions and user benefits. Examples of this are the Smart Actuator Profile, the Lighting and Indication Profile and the Smart Power Systems Profile.
The IO-Link Community is an organization dedicated to the further development, standardization and dissemination of IO-Link technology. It was founded as part of the PROFIBUS User Organization (PNO), which in turn is one of the largest communities for industrial communication worldwide. It is made up of a large number of manufacturers, developers, system integrators and users who work in the fields of automation technology and industrial manufacturing.
As the technology continues to be developed and improved, more and more companies are recognizing the advantages of IO-Link. As a result, by 2023 there were already more than 35 million IO-Link devices installed, 8.4 million more than in the previous year. This is due not least to the ongoing development of Industry 4.0 applications and the Industrial Internet of Things (IIoT), for which IO-Link is ideally suited.
IO-Link nodes at a glance
Although IO-Link offers numerous advantages, implementation can present challenges, particularly in terms of staff training and integration into existing systems. The need for extensive planning and possibly also customization of the existing infrastructure can result in initial costs, but these are justified by the long-term savings and efficiency gains. To make the integration into existing systems smooth and efficient, it is definitely worth enlisting the support of an expert.
