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First introduced in 2007, WirelessHART has become the standard of choice for wireless communication with industrial field devices. Also known as IEC 62591, WirelessHART is the first international standard for wireless industrial field devices. Daniela Roth, marketing communications for MESCO Engineering GmbH, explains why the standard has become so well-accepted in such a short time. "WirelessHART fits well to HART technology with wired communication."
"Most all industrial customers are already familiar with HART," says Moore Industries International national sales manager Gary Prentice. "I believe it is this embedded familiarity that has given WirelessHART its head start. Moreover, most all of the asset management systems and hand-held communicators used for programming field devices are already based on HART. Wireless standards or protocols other than HART have to be further explained when it comes to seamless integration with other devices or existing legacy control and management systems."
Gary Cusick, president of MACTek Corporation, says, "The industry recognizes the benefit of a wireless solution based on the industry-standard HART protocol. Users expect a wireless solution to be based upon their existing devices and skill level. Also, WirelessHART technology is supported and implemented by a large number of device suppliers around the world.
"Third," Cusick continues, "WirelessHART is now field-proven, with more than 8000 networks (and more than 10,000 devices) working in process applications worldwide. Lastly, "users have confirmed that WirelessHART, is a simple, reliable and secure solution that truly addresses the needs of the process industry. Users have come to know that a wireless solution that claims to be everything to everybody is not a practical solution and will add unnecessary complexity to the solution."
Many of the 280+ members of the HART Communication Foundation are offering or preparing to offer WirelessHART devices. Jonas Berge, director of applied technology at Emerson Process Management, says, "WirelessHART has more supporting instrument suppliers than any other wireless industrial protocol. Interoperability is assured because they all use the same common application protocol: HART commands. All features for all instruments regardless of vendor can be accessed thanks to the HART standard."
Robert Schosker, product manager for intrinsic safety, HART, signal conditioners, power supplies and surge at Pepperl+Fuchs, notes, "Nearly 70% of all products shipped today incorporate the HART protocol. Integrating a wireless technology on top of a hugely successful standard protocol that’s simple, easy and already understood makes HART a viable—and trusted—option as a wireless
provider. Secondly, getting to the market first helped immensely. And almost every manufacturer of field devices offers HART as part of its product portfolio, making the availability of products easier and offering less risk to the customer."
Having identified HART as a good basis for a wireless instrument network,, the creators of WirelessHART needed to take into account the needs and requirements of the major end users of instrumentation. The major instrument vendors and organizations, such as the HART Communication Foundation, carried out customer surveys and received the same top three requirements: "Make it simple, reliable and secure."
Customers also said they needed a network that can monitor itself and repair problematic pathways automatically and in good time. Reliability was a key focus of the WirelessHART development team.
Another key focus was security. Data must not only be encrypted, but as recent malware attacks on field controllers have shown, it must also be authenticated to make sure it has not been changed since transmission.
Finally, one of the most powerful features of HART, and what has made it so successful, is its simplicity of operation. As with the wired HART protocol, a master device issues a command and a slave instrument responds. WirelessHART has to be more aware of power requirements, so has included additional features, such as reporting on exception or changing refresh/update rates based upon conditions.
WirelessHART is simple enough to work with for commissioning engineers, operators and maintenance technicians. The network has many automatic functions built in to simplify engineering—it is as simple as 4-20 mA.
While WirelessHART was designed for battery operation, there are many applications in which the transmitter will be wired for power, but not to signal. But it is in battery operation that users have to consider power.
The standard was designed specifically for low-power operation, less than 4 mA at 12 VDC. Update rate (how many times a minute the transmitter wakes up and takes a measurement and transmits data) affects battery life, as do cold, heat and other environmental considerations.
Several vendors provide WirelessHART devices with integral batteries that are approved for hazardous area classifications.
Emerson’s Jonas Berge says, "In a plant environment full of steel, you need mesh topology with multiple hops and multiple paths to ensure reliability. Only WirelessHART provides both true mesh technology with multiple hops and star topology (direct connection to the gateway for faster updates) if needed. It is self-organizing, so no undue effort is required to make it work—it works out of the box. Routing devices also mean a single gateway covers a large plant area. Other wireless technologies are star topology with limited hops. This requires a large number of backbone routers, which is impractical and costly to wire up in an existing plant."