By Alan Mathason, Emerson
Manufacturing companies and machine builder OEMs have been digitalizing their automation designs for decades. But in recent years, the iterative process of identifying and solving problems using data and technology to support the work of people has been termed digital transformation, which encompasses many aspects, from the plant floor up to the cloud. One trend within industrial digital transformation is that the number of field sensors and devices, and their capability and intelligence, have been increasing dramatically.
Along the digital transformation journey, users have certainly experienced success transitioning away from traditional hardwiring methods and toward more modern digital solutions for connecting with the growing number of field devices. However, as industry faces workforce challenges, there has been a renewed focus on choosing technologies that are easily deployed and supported by available operations and maintenance personnel.
At the on-machine and plant-floor level of operations, the IO-Link protocol, media, and compatible field devices often provide a superior solution for OEMs and end users alike. Considering the widespread and growing availability of products supporting IO-Link, designers must consider including this technology in their projects.
There are already many standard industrial digital fieldbuses for communicating with intelligent and data-rich field devices like input/output (I/O) systems, instruments/analyzers, and more. Examples include PROFINET, Modbus TCP and RTU, EtherCAT, EtherNet/IP, DeviceNet, and others. Some of these fieldbuses use specific wiring methods, while more modern versions are typically Ethernet-based. So, what is the attraction of IO-Link?
Digital transformation and industrial Internet of Things (IIoT) initiatives are built on data, much of which is sourced from the field. Although high and low-complexity field devices are relatively sophisticated data sources requiring equally complex communications, there are many basic discrete and analog devices, such as presence and pressure sensors, valve controls, and more which are gaining capabilities where digital signaling would be useful. Throughout their service lives, the configuration and diagnostic data trapped inside these devices need to be readily available to best manage the system and minimize customer downtime.
Historically, much of the I/O on machines and in automated manufacturing has been used for one-way signals — whether input or output — between the field device and the supervisory controller I/O system. Examples include:
• Discrete input signal from a photoswitch
• Discrete output command to a solenoid manifold valve
• Analog input signal from a basic pressure transmitter
• Analog output command to a pressure controller
Hardwiring requires significant field-installed conduit and wire, and the result provides just one signal. One global standard for augmenting analog signals is the HART protocol, which superimposes digital communications over analog hardwiring so users with the right host system can access extended configuration, diagnostic, and status information.
Therefore, many users lack a convenient way to implement important digital communications for much of their automation needs unless they commit to implementing complex designs and using costly products, which are impractical for many applications.
Examining IO-Link features
To address these and other concerns, IO-Link was developed to provide bi-directional digital communications between a field device and a master device in a form factor well suited for industrial installations. Specified by IEC 61131-9, IO-Link uses common unshielded three-conductor cables to supply the 24VDC power needed for typical industrial devices, and it offers connection distances of up to 20 meters. There are two port classes, A and B, with the latter capable of supplying more power. For additional cable reduction, IO-Link Wireless is a newer standard providing even more installation options.
A wired IO-Link architecture employs “masters,” which are connected using industrial Ethernet network “in” and “out” ports, and the modules are powered by 24VDC “in” and “out” ports, so the devices are easily daisy-chained to minimize cabling length and costs. Each master module can connect with several IO-Link field devices, typically 4 to 8 per IO-Link master (Figure 2).
An important capability with many models of an IO-Link master is support for simultaneous links to different hosts. For instance, an IO-Link master network could be connected to a host PLC via PROFINET for monitoring and control and to other hosts, such as a historian and an asset management system via OPC UA, MQTT, or Modbus TCP for supplying data (Figure 3). PROFINET is particularly attractive for mission-critical industrial systems, and it can be configured as a redundant ring supporting media redundancy protocol (MRP).
Field device wiring to master modules is simple and consistent. Users can select field devices and panel-mount masters, each using traditional wiring methods. However, for many applications, users are finding that surface-mount IP67-rated masters and connections made using standardized A-code M12 connectors provide the greatest advantages. These devices are simple to install and service compared with conduit and wire, while traditional IP20 and IP67 form factors are complementary and can be mixed and matched as needed.
IO-Link provides a superior balance of performance and efficiency for many applications, and it has many enhancements, which make it easier to deploy and maintain than most traditional protocols. IO-Link devices can transmit up to 32 bytes of essential data cyclically and other supplementary data asynchronously. More than one process value — whether discrete or analog, input or output — is available at all times, and users can perform device configuration and access diagnostics remotely via their host system.
Whereas HART devices require commissioning to be repeated for each device, IO-Link master devices support the concept of capturing device configuration “recipes,” so all customization settings can be saved and replicated for subsequent similar devices. More importantly, replacement devices will auto-configure to match the setup of the previously installed device, so even inexperienced technicians can replace field components and get back up and running quickly.
Filed Under: I/O modules