IO-Link – Communication standard for Industry 4.0

In the age of rapid technological progress and the changing production landscape, efficient communication between devices and systems is playing an increasingly crucial role. The IO-Link communication standard is standardized in the IEC 61131-9 standard and has established itself as a cornerstone for Industry 4.0. It enables seamless and intelligent interaction between sensors, actuators and the control plane.

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The implementation of IO-Link brings a wealth of benefits in the industrial environment. A central aspect of this is the increased flexibility in the integration of components. The unified interface allows sensors and actuators from different manufacturers to communicate with each other, which consequently makes it much easier to adapt and expand production equipment. This also helps to shorten the innovation cycle and subsequently accelerate the time-to-market for new products.

Interoperability

The availability of a diverse selection of IO-Link sensors allows companies to select the right components for their specific applications and thus make the most of the benefits of interoperability. From proximity switches to pressure sensors to temperature and level sensors, there are a variety of devices offered by different manufacturers.

Diagnostic capability

Another significant advantage is the advanced diagnostic capability of IO-Link. Thanks to bidirectional communication, sensors can not only provide measured values, but also additional information about their condition and performance. This real-time data enables preventive maintenance and consequently significantly improves plant availability. In addition, IO-Link simplifies the parameterization of devices, as settings can be made via the control level, but without having to physically intervene on site.

The communication is based on a serial point-to-point connection between an IO-Link master and an IO-Link-enabled sensor or actuator. This connection is made via conventional three-wire wired cables and thus enables reliable transmission of digital data and commands. The basic communication protocol is based on an asynchronous, half-duplex procedure in which telegrams are used that consist of a start bit, data bits, parity bit and a stop bit. This structure ensures reliable and error-free transmission of data, while communication takes place at cyclic intervals, with the IO-Link master requesting data from the connected devices.

Different communication classes of the IO-Link standard

Communication always starts with a “wake-up” event, followed by a “start-up” message from the master to determine the supported speed of the device. Further communication parameters are read, as well as the manufacturer ID and device ID are checked in order to finally validate the communication. Within the standard, three transmission speeds are specified, known as communication classes: COM1, COM2, and COM3. Each class offers different speeds, making it suitable for specific application requirements.

COM1: COM1 is the slowest class of communication. It is characterized by longer communication cycles, which are particularly relevant for applications where stability and precision play a greater role than a fast refresh rate. The transmission speed of COM1 is 4.8 kbit/s.

COM2: COM2, on the other hand, offers medium transfer speeds. It is suitable for applications that require a good balance between speed and precision. The transmission speed of COM2 is 38.4 kbit/s. This speed class can be used by processes that require a higher amount of process data.

COM3: The COM3 speed class offers the highest transmission speed in the IO-Link standard. It is characterized by the shortest cycle times and is therefore particularly relevant for applications where a high speed of data refresh is crucial. The transmission speed of COM3 is 230.4 kbit/s.

Flexible communication thanks to IO-Link

The selection of the appropriate communication class depends on the individual requirements of the application. The flexibility of these different speeds makes it possible to find the optimal balance between speed, precision and data transfer rate. Overall, the different communication classes contribute to the fact that IO-Link communication can ultimately be efficiently adapted to the respective application needs.

The transmitted data is accessed via the IO-Link master. This intelligent gateway thus acts as an interface between the sensors and actuators on the one hand and the higher-level controller on the other. The IO-Link master not only collects data from the connected devices, but also translates it into a format that is understandable for the controller. Consequently, this enables a smooth integration of the data into the production process and subsequently opens up various possibilities for comprehensive analysis and monitoring during the running process.

The different IO-Link masters each support different communication protocols for connecting to the controller. These protocols can include Ethernet-based standards such as Profinet, EtherNet/IP, Modbus TCP or MQTT, but also fieldbuses such as Profibus or DeviceNet. The choice of protocol always depends on the requirements of the application and the company’s pre-existing infrastructure. This enables seamless integration of IO-Link devices into existing networks and facilitates communication between the components of the automation systems.

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In today’s industrial landscape, there is a wide range of manufacturers that offer IO-Link masters. Industry giants such as Siemens, Pepperl+Fuchs, Balluff, Turck and IFM Electronic are well-known players in this field. These companies offer, among other things, a variety of IO-Link masters, which differ in terms of, for example, the number of ports, supported interfaces and additional functions.

The IODD (IO Device Description) is a standardized, electronic device description that contains specific information about an IO-Link-enabled sensor or actuator. This description ensures that the communication between an IO-Link master and a connected device runs smoothly across manufacturers and that all relevant data is interpreted correctly.

Features of IODD

1. Automatic Configuration: Thanks to the IODD, an IO-Link master can automatically detect and set up the configuration parameters of a connected device. This subsequently significantly reduces the manual effort and also minimizes possible sources of error during device configuration.
2. Advanced Diagnostics: The IODD makes it possible to retrieve detailed diagnostic information from IO-Link devices. This includes, for example, status messages, error codes and operating conditions. This diagnostic data is essential for preventive maintenance and also improves system availability.
3. Flexibility for device replacement: When an IO-Link device needs to be replaced, the IODD allows for a smooth restart. The master can automatically extract the required configuration data from the IODD of the new device and apply it.
4. Access to advanced features: The IODD can describe additional functions and parameters of a device that go beyond the basic functions. This allows for more precise adaptation and fine-tuning of the devices for specific application requirements.
5. Future-proofing: IODD can support updates and enhancements to device features. This makes it possible to add new features to IO-Link devices without compromising compatibility with existing systems.
6. Reduced commissioning times: By using IODD, commissioning times are shortened, as all necessary device information is already available digitally. This speeds up plant setup and increases efficiency.

Overall, the IODD contributes significantly to the intelligence and usability of IO-Link devices. It enables transparent communication, optimizes configuration and simplifies maintenance.

Communication takes place via a network protocol based on the Internet Protocol, such as Modbus TCP, MQTT or HTTP, and requires an external IO-Link master that supports the Internet Protocol. The system can then connect to the master with a node for the selected network protocol via Node-RED and then retrieve the desired values. The received values can then be transferred directly from Node-RED to an internal or external database, such as the InfluxDB Times Series Data Platform. Alternatively, the data can be analyzed and/or merged directly in Node-RED or an outsourced analysis module. The results can then be visualized in a dashboard or made available to other network participants via MQTT on a broker.

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