How EtherNet/IP Has Changed Linear Position Sensors

By Matt Hankinson, global market segment leader, MTS Systems Corp., Sensors Division

Editor's Note: This article is adapted from a comprehensive white paper, "Magnetostrictive, Absolute, Non-contact Linear-Position Sensors: EtherNet/IP and Industrial Ethernet for Factory Automation." Download the free, complete white paper that has additional information about how the Ethernet functions in motion control; the types of protocols available for absolute, linear position sensors; the evolution of industrial Ethernet protocols; how magnetostriction works; and a case study about how EtherNet/IP^TM-controlled positioning sensors helped a company cut costs.

Ethernet technology has been around for more than three decades, so it’s natural to apply it to industrial automation applications. Posi­tion feedback devices historically have used analog signals (voltage or current) or dedicated fieldbus networks such as CANbus, PROFIBUS^® or DeviceNet^TM for communication at the device level with motion controllers.

Meanwhile, control-level networks manage communication between controllers, which might then go through a gateway before reaching the corporate Ethernet network. How do you meet the connectivity demands in the factory while ad­dressing the real-time performance needs for motion control? Can this be achieved with common network architecture?

What Users Need

The challenge for industrial Ethernet networks in automation is achieving the required speed and determinism. Typically, Ethernet packets exchanged on a network don’t come with consistent delivery times at the level required for automation applications.

In addition, the requirements vary with different types of components. Drives and other high-speed devices, for example, may require update times of 1 ms or faster. Other devices, such as controllers or terminals, might only need 10-100 ms updates.

Industrial Ethernet adoption in the plant has grown considerably, because it offers shielding and robustness for harsh manufacturing environments. These solutions follow the IEC 61158-2 for the physical layer and IEC 61784-1,-2 standards for measurement and control profiles, and are open for a variety of devices to adopt.

A Closer Look 

To achieve real-time capability, EtherNet/IP divides commu­nication into explicit and implicit message types. The Quality of Service (QoS) feature in EtherNet/IP verifies that implicit messages are allowing that your components already are tested for conformance by the ODVA. The ODVA provides a Declaration of Conformity (DOC) for every product that complies with the requirements for EtherNet/IP and makes them available on its website; look for the EtherNet/IP Conformance Tested logo.

Users can implement linear or ring topology depending on the fault-tolerance requirements for the application. Linear topology is simpler and conducive to applications with a linear layout, such as conveyors. Ring topology adds fault tolerance capability by rerouting traffic within when a link failure occurs. The Ring Supervisor monitors the response as it beacons, and reconfigures the network within milliseconds if a link is broken.

Some devices offer Device Level Ring (DLR) capability to directly connect to the ring rather than to an external switch. The switch is essentially embedded directly into the device. This provides device-level network rerouting and failure point identification to improve reliability and network recovery time.

One of the advantages of EtherNet/IP is the ease for adding new devices to the network. Adding a linear position sensor to a network involves simply setting the IP address, attaching the sensor to the network, and configuring the controller parameters.

MTS Systems Corp., Sensors Division, based in Cary, North Carolina, is a participating Encompass^TM Product Partner in the Rockwell Automation PartnerNetwork^TM. The company supplies magnetostrictive linear position and liquid level sensors.

^{The Journal From Rockwell Automation and Our PartnerNetwork™ is published by Putman Media, Inc.}