Smart Ethernet in New LDT for Automation Industries

Joe Feeley is a former editor in chief for Control Design and Industrial Networking. A host of automation solutions require accurate feedback of continuous position to improve productivity and efficiency, regardless of the application environment. A traditional, preferred approach typically uses analog signal feedback. However, analog signals are limited by resolution, and the signals are prone to degradation over long cable runs. In addition, each axis needs its own dedicated cable. Ametek Factory Automation offers a new alternative with its ReadyLink EtherNet/IP network linear displacement transducer (LDT), which uses field-proven, magnetostrictive technology to provide absolute non-contact feedback and resolution to one micron.

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"There are times when the desired resolution isn’t achievable using an analog device," says Blake Cawley, business development manager for Ametek Factory Automation. "There are many times when the customer is looking to update analog machinery, particularly when he has other EtherNet/IP devices on his machines, so continuous position, motion and velocity monitoring of equipment can be incorporated into the control system process via the network." Cawley adds that this also is a good solution when linear motion travel with multiple stops or position points is required.

"ReadyLink EtherNet/IP LDT is a smart device," Cawley says. "It has a RapidRecall network configuration module with a built-in web page to help aid in configuration of the LDT. A static IP address can be assigned via the web page, or by using three rotary DIP switches to set the last octet manually. The RapidRecall module also stores all user configurations. Once configured on the LDT, these settings can be uploaded and stored by the module. If the LDT ever needs replacement, the module can be removed and installed on the replacement unit, and all of the user configurations are restored without the need for a network technician to configure the sensor."

The intent of the web pages is to provide nearly the same functionality that exists through the network interface. The home web page is loaded when the module’s IP address is specified by the user’s web browser.
 

The network LDT is designed to operate anywhere between 7 to 30 Vdc at 2.3 W of power. "With this wide-ranging supply, the same unit can be used in 24-V industrial or 12-V mobile applications," Cawley says. "A key advantage with the wide-ranging supply is that on long cable runs, users typically need not worry about voltage drop to the incoming power, eliminating the need for a separate power supply to power the LDT."Among the unique features built into the network LDT, Cawley says, are its position and velocity upper and lower limits. Users can program values into each of these limits. If the position or velocity of the LDT exceeds the limits, the device transmits a unique alarm bit for each alarm condition. "The device provides alarm condition detection and annunciation based on position and velocity conditions, which improves response speed to defined fault conditions, and avoids having to write ladder logic and tying up process time to monitor the conditions," Cawley says.Data is communicated over the Ethernet network using I/O messaging for time-critical data, such as position and velocity status, as well as explicit messages for configuration data, such as position scaling, resolution and count direction, among other parameters.To aid in troubleshooting, the Network LDT is equipped with four network LEDs and a tri-color LDT status LED. The four top-row LEDs will display diagnostics and network status. The bottom-row LDT LED will display the status of the linear transducer. "The network LDT has an auto-tuning capability and automatically compensates for non-standard magnet assemblies or adverse application conditions," Cawley states. "The automatic gain control feature automatically searches and finds the magnet on power up. If power is applied without a magnet on the LDT, the LED will turn red to indicate that no magnet signal is detected."The new device is available in two package styles. The 953N is a rod-style package suitable for installation into hydraulic cylinders. The 957N Brik low-profile-style package incorporates the same electronics, but is housed in an aluminum-style extrusion.