Why develop IO-Link?
In the past, each fieldbus (such as MODBUS and PROFIBUS) had its own connector for connecting sensors or actuators to supported protocols. This meant that automation engineers had to understand the details of how they worked and select the correct cables and input cards. To address these issues, manufacturers incorporated fieldbus interfaces into their devices. However, this approach became impractical as sensor and actuator sizes continued to shrink. Beyond the smaller size, manufacturing processes required sensors to transmit readings of physical quantities such as temperature and pressure and to be remotely configurable (bidirectional communication) via process controllers. These factors were the primary drivers behind the development of IO-Link as a globally standardized interface, compatible with small devices from all equipment manufacturers. These devices can be easily integrated into any network (fieldbus or industrial Ethernet) using an IO-Link* master. IO-Link sensors also needed to be backward compatible with legacy binary sensors for easier integration into existing factory systems.
How does IO-Link work?
An IO-Link system consists of slave stations (sensors or actuators) and an IO-Link master station. See Figure 1. Each slave station can only connect to one IO-Link master station, but an IO-Link master station can serve multiple slave stations.
Figure 1 - IO-Link System
The IO-Link master station acts as a gateway, bridging the link between the connected slave stations and the upstream industrial network used by the process controller (Figure 2).
Figure 2 - How IO-Link is integrated into factory automation architecture
IO-Link is a serial digital point-to-point protocol in which each slave device connects to a physical port on the IO-Link master. This protocol eliminates the need for complex addressing, uses standardized connectors (typically M8 or M12) and unshielded three-wire cables, and is simple to install and inexpensive.
• The IO-Link master port has the following four working modes:
•IO-Link: The port is used for bidirectional IO-Link communication.
•DI: The port behaves like a numeric input.
• DQ: The port behaves like a digital output.
• Disable: The "Disable" mode can be used on unused ports.
•IO-Link data communication can be periodic or non-periodic.
• Periodic communication occurs during normal operation, with the IO-Link master driving the transmission of "process data".
Non-periodic data is transmitted "on request" and may contain configuration or maintenance information (service data). For example, an IO-Link master might send a new configuration to a slave after it powers on, or request configuration from a slave before it shuts down. Event data is also non-periodic, appearing when unexpected events occur and being reported to the controller according to their severity (notification, warning, and error).
Where can IO-Link be used?
IO-Link is ideal for factory automation applications, including:
• Automated assembly lines: Enable rapid installation and quick changeover to production operations.
• Machine tools: Sensor parameter settings (temperature, pressure, airflow) enable quick setup and make faulty sensors easier to identify and replace.
• Conveyor belt: Speed and stop point can be dynamically changed according to the load.
• Personalized manufacturing/small-batch production: IO-Link is easy to configure remotely, giving flexibility to personalized manufacturing.
• Hydraulic system: IO-Link meets all critical requirements, including reliable signal transmission, temperature, pressure, and level control.
What are the limitations of IO-Link?
It is important to note that IO-Link is not designed to support all types of sensors or actuators. It can only transmit a maximum of 32 bytes of process data per cycle, making it unsuitable for transmitting the large amounts of data generated by devices such as cameras or scanners used in industrial imaging equipment. A production cycle of approximately 2ms (typical) is sufficient for most factory automation requirements, but not for high-speed applications. Furthermore, the cable connecting the slave station and the IO-Link master station must not exceed 20 meters.
How does IO-Link empower sensors or actuators?
Analog Devices (ADI) provides IO-Link slave and IO-Link master physical layer interfaces/transceivers (PHYs). Our 4-port/8-port IO-Link master and slave transceivers integrate buck regulators and LDOs, and feature ±60V cable interface protection, enabling stable and reliable operation in harsh industrial environments.
