Electric utility stretches sensor coverage

Multi-drop WirelessHART supports new temperature points to improve efficiency.


One WirelessHART adapter can carry data from up to eight temperature sensors using the multi-drop configuration. Courtesy: Duke EnergyProgress Energy (now Duke Energy), a publicly-owned U.S. electric utility, uses WirelessHART communication to improve performance efficiency and output in multiple plant locations. The company keeps plant equipment and systems running smoothly using HART technology for testing, troubleshooting, and verifying performance standards on new and upgraded equipment.

Progress Energy maintains 240 temperature and pressure transmitters and some flow devices at 32 plant locations. Previously, these devices had been hardwired to HART multiplexers to accommodate far-flung cable runs from one site to the next across facilities and even over streets to conduct tests.

With the introduction of the WirelessHART standard and the availability of network WirelessHART adapters that conform to the standard, the company sought to replace its aging test equipment and streamline testing with a new wireless system.

Dick Fletcher, Progress Energy’s performance testing group team manager, notes that the company had a major investment in existing HART smart transmitters. “The logical thing to do was get a common data acquisition system to be shared across the system by performance testing,” he says. “A system that could handle a variety of instruments, interface with standard commercial instruments using standard protocols and be easy to configure.”

Project objectives

“We had to get the best bang for the buck,” says Fletcher, “and that meant that we had to maintain compatibility with our existing investment in HART-enabled transmitters.” The goals were to develop a common field data acquisition system; allow equipment sharing across the system and minimize the total company inventory; take advantage of HART’s ability to collect data digitally and in multi-drop mode; ease the installation of the test equipment to minimize time and effort, and benefit from a flexible, easily expandable and easily configurable system.

Using recently developed HART-based products, like the MACTek Bullet which supports up to eight HART transmitters in field-proven HART multi-drop mode, meant a wireless gateway could replace failing multiplexers, and far fewer cables would need to be deployed for temporary test transmitter installations.

“The economics of a hybrid wireless-wired HART system became more feasible for us to consider. While we were able to show no connection to the plant’s cyber assets, we were impressed with the security of the encrypted HART protocol,” says Fletcher, who did have one caveat to using the wireless network adapters. Because WirelessHART technology uses the same 2.4 GHz frequency band as Wi-Fi, he was concerned about range limits and the possibility of interference between objects and antennas.

However, in actual use, the HART instruments don’t have to be in line-of-sight to establish a network and, Fletcher notes, “the WirelessHART radio links will form in circumstances that Wi-Fi couldn’t hope to achieve, and they just work. Wi-Fi was designed for speed, while WirelessHART is designed for data reliability.”

Benefits realized

The advantages of the new system were apparent, from up-front cost to the long-term reliability of the data acquisition system and, in turn, the reliability of assets across Progress Energy’s 32 plants. Labor savings were evident from the first outing with the new system.

“I estimate that we saved 100-150 man-hours,” says Fletcher. “On a small test, we saved about six man-hours on a setup that took about 10 man-hours to set up using wireless. With an average of 15 tests a year and saving an average 33 hours of labor each, that works out to $20,000 savings per year.”

Beyond up-front savings, the new system reduces cabling, as the radio links eliminate situations that placed cables at risk of damage. “Along with the streamlined process for data acquisition, we get a better picture in real time of how our test equipment is performing and communicating,” says Fletcher.

While HART is a hybrid analog/digital specification, wireless data transmission is all-digital. This allows HART technology to transcend its heritage as a diagnostic tool and enter the world of digital bus functionality. Fletcher notes the protocol is built for redundancy and reliability.

In multi-drop mode, the analog signal isn’t used; instruments use the 4-20 mA signals for power, but process variables, from tags to diagnostics and process variable measurements, are transmitted digitally. So, in a sense, the technology might open the door for new applications previously thought to be the sole domain of digital fieldbus networks, such as condition monitoring and asset management.

JUAN , Non-US/Not Applicable, Mexico, 05/16/13 07:04 PM:

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