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Kicked Up a Notch

New testing and registration procedures further lock in interoperability

In August, the HART Communication Foundation announced the release of the WirelessHART™ Device Registration Procedure document that outlines the testing and registration requirements for WirelessHART devices. The Procedure is an integral part of the HART Device Registration Program. The program is designed to ensure device interoperability of both wired and wireless HART-enabled devices.

“The release of the registration procedure is the crowning achievement in our progress toward delivering fully interoperable wireless products based on the HART Standard,” says Ed Ladd, Director of Technology Programs. “The requirements it sets forth assure the interoperability of wireless devices in a multi-vendor environment and the conformance of those devices to the requirements of the HART Communication Protocol Specification.” 

HART users have the largest selection of device types, system solutions and vendors. More than 30 million HART devices are in the field, including more than 1,000 types of devices produced by over 220 different manufacturers. Every day, more users rely on the technology’s promise of interoperability to harness the power of continuous communications among new and existing HART devices.

The HART Communication Foundation supports their confidence with a rigorous test program that verifies compliance with the HART specification. “Every device comes to us and is 100% verified from a protocol standpoint,” says Ladd. “Our lab tests wired and wireless in all HART Protocol revisions, HART 5, 6 and 7 – they can register to any level.”

All devices that claim HART compliance must be tested: field devices; interfaces such as modems, multiplexers and I/O systems; HART masters including systems and handhelds; and device description (DD)-enabled host applications.

“Unfettered interoperability is our goal for all devices implementing the HART Protocol,” says Ladd. “Therefore, the Protocol specifications and Quality Assurance and Device Registration Procedures are all written to ensure the interoperability of HART-enabled products.”

Since 1993, vendors have been permitted to develop testing procedures on their own and submit the test results to the Foundation. In 2008, the Foundation’s board of directors mandated required, independent verification testing to register HART devices, whether wired or wireless.

Ladd continues, “Products undergo many levels of testing, and the test specifications that are outlined in the HART Test Program standardize and eliminate the need for each manufacturer to develop its own test to validate Protocol compliance.”

Manufacturers still test their devices, but they use new standardized tests and procedures. Ladd adds, “Manufacturers must confirm the test results through the Foundation’s Quality Assurance and Device Registration Procedure. Manufacturers must perform the tests and certify the results. Then they send a device along with complete documentation to the Foundation for verification. Through independent testing the Foundation performs 100% verification and validates that the device and its test results have met the Protocol requirements.”

How a HART Device Is Tested

Manufacturers are required to fully test their devices using the tools available and the procedure outlined by the Foundation prior to submitting their devices for Foundation registration. The Foundation independently validates that the device and data submitted meets the Protocol requirements.

Regardless of whether it is a HART or WirelessHART device, the testing process is the same:

  1. Manufacturer tests the device
  2. Manufacturer submits test data for completeness review prior to submission
  3. Manufacturer sends complete test data, device and setup information to the Foundation
  4. Foundation performs 100% verification of device comparing the manufacturer’s data to the verification test data from the test at Foundation lab.
  5. The last test to be performed is a stress test that sends two million messages to the device. The device can miss no more than 20 messages out of two million, a failure rate of not more than 0.001%.
  6. Once the device is verified, a certificate is issued, the website is updated and the device can carry the “HART Registered” mark.

After the manufacturer has tested the device, it sends a written report with the test data and results, manuals, instructions, and the device to the Foundation lab. There, “We do 100% verification to see that they got what we got, and that they meet the standard,” says Ladd. “By us running the tests and verifying that they pass, we ensure interoperability.”

The Foundation lab tests:

  1. Every command
  2. How the data layer works: timing and test that devices don’t get kicked off.
  3. How the physical layer works: the wave shapes on the 4-20 mA line
  4. The universal application layer: Every device must include the UAL for interoperability.
  5. The common practice application layer: This test is optional, but if they use it, it must do what the specification says.

Devices that pass the tests are provided with a Certificate of Registration and are authorized and encouraged to display the “HART Registered” mark on the device, documentation, and promotional materials.

Interoperability and interchangeability

“Ensuring interoperability is critical,” says Ladd. “If you’re replacing a device at 2 a.m., you know it’s going to work no matter who manufactured it. That’s what the registration process is all about.”

As the number of HART products installed globally continues to grow, it becomes increasingly more important that all manufacturers ensure their devices are compliant to the HART Protocol Standard. “It has always been a requirement,” says Ladd, “that any HART-enabled device must be able to replace any other similar device, regardless of manufacturer.

“That means that any new HART 7 device, wired or WirelessHART, is backward-compatible with the entire globally installed base of HART instruments. It also means that HART-enabled devices have a very low risk of failure or bad application, and the cost of ownership is lower because you can reduce inventory. One device can be configured for multiple applications.”