Last meter to the Internet of Things

Device networks can serve as a cost-effective extension in the last meter that connects industrial devices to the Internet of Things (IoT). Improve IP connectivity in the last meter from the industrial control system to field devices with IO-Link or HART (wired or wireless), to make today’s plants more future-ready for industrial IoT.

By Shannon R. Foos, Kevin Zomchek March 10, 2015

A significant hurdle stands in the way of industrial operations attempting to realize the full benefits of the Internet of Things (IoT): How to connect billions of sensors, actuators, and other instrumentation now beyond the reach of the Internet Protocol (IP)? Two innovative technologies can support that vital connection to IoT, extending the increased operational data, enhancing productivity, and improving reliability that come with the IoT.

The last meter to the IoT is being bridged by IO-Link device communications for discrete applications [offered by Profibus & Profinet International (PI)] and HART and WirelessHART for process application communications [from the FieldComm Group, the merged Fieldbus Foundation HART Communication Foundation]. Both communication protocols work with networks based on EtherNet/IP [an Ethernet protocol network from ODVA] to connect sensors to control systems and business-level enterprise systems.

With instrument data available on EtherNet/IP, industrial operations can capture the real-time, actionable information they need to achieve operational efficiencies, increase productivity, and achieve the full benefits of the IoT.

IO-Link for discrete applications

In an evolving IoT world, companies are looking to get more intelligence from every device. But in discrete applications, such as packaging or automotive facilities that use large amounts of sensors, it is simply not cost-effective to replace existing instrumentation with IP-enabled devices. IO-Link was developed to create a cost-effective, last-meter connection between sensors and control systems for seamless data flow.

There have been past attempts to enable sensors on different communication protocols, such as Profibus [PI] or DeviceNet [also from ODVA], which required a different network to connect to the devices. However, many sensor users pushed back on those efforts because it doubled the number of products (networked and non-networked) to support on machines. It also involved learning a new protocol-even if only a subset of the total sensors on a given machine required more than on/off information, which was often the case.

IO-Link has become a suitable compromise for this dilemma by offering access to a wealth of information cost-effectively, while operating in conjunction with existing IP networks.

This access to device-level data means industrial operations don’t have to delay their needs for smarter machines while waiting for all sensors to have IP accessibility. IO-Link offers a simple solution to increase connectivity throughout discrete applications. IO-Link communicates over the same three-wire conductors and can use the same configuration software currently used with EtherNet/IP networks, so getting the sensor data to IP is relatively seamless. All sensors installed on a machine can support IO-Link, and those connected to an IO-Link master interface will take advantage of the technology with diagnostics. This eliminates the need to learn a new protocol and limits the additional expenses to those sensors that are actively using the IO-Link technology.

To access the IO-Link functionality with technology already in the plant, manufacturers simply remove the discrete card and install an IO-Link card, the aforementioned IO-Link master. Many sensors featuring embedded IO-Link cost and act the same as the standard I/O sensors that manufacturers are already using until connected to a master. But interfacing these sensors with an IO-Link master "wakes up" the advanced functionality in the sensor, giving the user access to all the data and configuration capabilities IO-Link has to offer. This means users have the flexibility to install IO-Link sensors as standard IO today and activate IO-Link functionality later, as needed, without having to install costly new wiring or sensors. This makes IO-Link an excellent forward- and backward-compatible solution for sensor suppliers and users. 

With or without diagnostics

The flexibility to interchange "standard" and IO-Link enabled sensors allows users to be selective. Not all machines or sensors need additional diagnostics. With the IO-Link master, users can choose which sensors to enable with IO-Link—gaining benefits without information overload. Although all machines can benefit from IO-Link, it’s not needed throughout the machine. In fact, less than 20% of the sensors on a machine are typically at risk of physical damage—these are the areas where the additional diagnostics offered by IO-Link would be most beneficial.

With IO-Link, users have access to new information that flows from the devices through IP to higher levels of the system. This could include diagnostics about sensors that are broken or not performing at optimal levels. An example might be the monitoring of a photoelectric sensor located near a cutting operation where significant debris can accumulate on the sensor lens. Currently, most machine builders use compressed air to periodically blow debris off the sensors regardless of how dirty the sensor might be. The IO-Link sensor can inform the control system to initiate compressed air or send a maintenance person to clean the sensor only when necessary. This reduces machine downtime, since it optimizes predictive maintenance, and reduces compressed air use, and related expenses.

In another example, consider how proximity sensors are used to detect objects moving along a conveyor. If a machine gets out of alignment and shears off the head of a standard sensor, the controller no longer receives updates from the device that there are products being sensed. Yet the machine will continue to operate, and operators often have no way of knowing that critical data is not being collected until production is interrupted. But if that proximity sensor is IO-Link enabled, an alarm will trip and tell the control system that the sensor head has failed. The diagnostic is not a direct measurement, but it alerts the system that the data is no longer valid. Additionally, the damaged sensor could more easily be pinpointed for quick replacement.

Wired, wireless HART for processes

The promise of instrument data throughout the enterprise has been around for many years in process applications with HART. However, for many installations, hardwiring devices can be arduous. In applications, such as tank farms or mining operations, that span many miles, hardwiring devices through point-to-point connections is difficult, time-consuming, and expensive, even more so when redundancy is required.

Those geographic and environmental complications have led to the need for technology with a broader reach. WirelessHART offers wireless connections to sensors that measure pressure, temperature, and volume in process applications.

The WirelessHART gateway is IP-enabled in multiple variants, including EtherNet/IP. Similar to other wireless networks, existing devices can be converted to WirelessHART to create a robust infrastructure that allows greater connectivity and generates a wealth of new data.

WirelessHART offers greater flexibility for a variety of applications, including device monitoring and diagnostics. For example, if a pipe is empty when it should be transporting a product, the sensor will alert the operator rather than simply showing an erroneous flow measurement. This helps the operator classify the plant deviation as an operations issue rather than a maintenance issue.

Similar to IO-Link, diagnostics are not direct measurements. Sensors enabled in HART devices give an inside view into the equipment with device information that can be used for predictive maintenance. This improves the reliability of the process, plant safety, and data security, and can reduce the cost of maintenance and unplanned downtime. 

Device data, where needed

HART devices also work seamlessly with EtherNet/IP on standard IP networks offering complete connectivity. Before, device data was limited to the control system, but now data from the process floor can travel throughout the plant, offering operators access to additional valuable data. Granular data availability optimizes every aspect of the operation—from troubleshooting problems on the plant floor to inventory or production capacity decisions on the business side. When operators have more asset knowledge, more auditing and verification are possible, which leads to increased process safety and data security. 

Connecting industrial IoT

The IP connectivity from the industrial control system through the gateway—either IO-Link or HART—closes the last meter to provide connectivity to field devices. These two networks allow industrial operations to bridge to an IP network as seamlessly as possible, making today’s plants more future-ready for the industrial IoT.

DeviceNet and EtherNet/IP are trademarks of ODVA Inc. HART and WirelessHART are trademarks of the HART Communication Foundation (now FieldComm Group). IO-Link and Profibus are trademarks of Profibus & Profinet International (PI).

– Shannon R. Foos, PE, is segment manager, asset management and fieldbus, and Kevin Zomchek is a marketing manager, network components, both at Rockwell Automation on behalf of Industrial IP Advantage; edited by Mark T. Hoske, content manager, Control Engineering,

ONLINE in March, this article has more information and links to related resources. Also see Ethernet and wireless webcasts at 

Key concepts

  • For the industrial Internet of Things (IoT), connecting field devices to Internet Protocol can be described as connecting the last meter.
  • IO-Link device communications help connect discrete applications to IoT.
  • HART and WirelessHART help connect process applications to IoT.

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About the authors

– Shannon R. Foos, PE, segment manager, asset management and fieldbus, Rockwell Automation, is an expert on process network, integration, and asset management topics. She has 20 years of experience in process industries and has focused on making facilities smarter for the last decade. She holds a bachelor of science in chemical engineering from The Ohio State University and is a licensed professional engineer in control systems.

– Kevin Zomchek is a marketing manager, network components at Rockwell Automation with almost 20 years of expertise in multiple network protocols and control architecture implementations. He holds bachelor of science and master of science degrees in electrical engineering from Marquette University.