Figure 1. IO-Link sensors, actuators, masters/hubs, and media offer a flexible architecture for the enhanced monitoring, control, and cloud connectivity needed for delivering intelligent equipment.

Throughout the commercial, laboratory, and industrial sectors, users are demanding that equipment of all types be more capable and automated. Smarter systems deliver improved operating performance, and they are also easier to use and maintain. Designers accomplish these goals by installing more instrumentation, accessing greater amounts of data, and providing greater controller capabilities with streamlined connections to a variety of field devices.

Over the years, various electrical and electronic connectivity methods have been developed and become standardized. There is not yet a “one to rule them all” connectivity technology, but a digital communications interface called IO-Link has gained traction in recent years and now provides a readily available, cost-effective, right-sized option for many applications.

Traditional connectivity between controllers and field devices has long employed hardwired discrete and analog input/output (I/O) signals — they are simple and effective, but burdensome to install and limited to a single data point per connection. Serial RS232/RS485 data transmission became possible in the 1960s and continues to deliver a proven way of transmitting significant amounts of data bi-directionally, but the associated wiring and programming effort can still be sizable. Industrial field buses have used both proprietary and open protocols, transmitted via specialized cabling or even 4-20mA wiring, to provide more robust communications than basic serial, although usually at a higher installed cost.

Taking a giant leap ahead, Ethernet was standardized in the 1980s and is often considered the modern networking technology of choice for rapidly transferring massive quantities of data. While industrial-specific protocols and ruggedized media and hardware are making it possible to use Ethernet variants on equipment and in harsh environments, many basic devices simply are not available in Ethernet versions.

To address these and other issues, IO-Link has been developed and is increasingly being adopted as a way of supporting up to 32 bytes of responsive bi-directional communication between a programmable logic controller (PLC) or other host system and a field device.

IO-Link is specified in IEC 61131-9, as an open standard with the following basic characteristics:

  • IO-Link field devices — both sensors and actuators — can operate in a standard I/O (SIO) format, or in the full IO-Link format.

  • An IO-Link “master” transmits hardwired I/O or IO-Link communications to a host using an industrial Ethernet protocol, such as EtherNet/IP.

  • An IO-Link “hub” can consolidate up to 16 discrete hardwired I/O points and communicate the information with a master using IO-Link.

  • Connection to each IO-Link field device uses standard unshielded three-wire cables to provide power and signaling for each device, at distances up to 20 meters.

  • Cables are connected using standard key-coded M12 fittings, and components are available in IP67-rated versions, making them suitable for surface-mounting without enclosures.

The IO-Link architecture provides many flexible options for efficiently installing sensors and actuators throughout equipment (Figure 1). Some master modules support the industry-standard MQTT protocol, so they can simultaneously transmit data to the cloud, even as a local controller is interacting with them.

Analog process instruments for flow, level, pressure, and temperature are available in IO-Link versions. In addition, IO-Link is economical enough to be built-in-to basic field devices such as photoelectric sensors, proximity sensors, level switches, and even pushbuttons and beacons.

Figure 2. A host can monitor and control a wide range of process values, diagnostics, and configuration parameters, as indicated in this AutomationDirect PLC data view.

IO-Link is used to rapidly transmit significant data beyond the primary input or output signal. Users can access secondary values, status information, and diagnostics (Figure 2). IO-Link enables field devices to be configured from the host, and it supports quick field device replacement by means of automatically restoring the proper configuration to a newly installed device.

IO-Link is a digital advancement combining the essential electrical and electronic characteristics of other connectivity methods. The resulting devices and architecture are enabling designers to create more intelligent equipment, streamline installation, and reduce overall costs.

This article was written by Kevin Kakascik, Technical Marketing Engineer, AutomationDirect (Cumming, GA). For more information, visit here .