Lohmann says, "With a HART Multiplexer, a short process shutdown will probably be required during the installation."
He goes on to note that there are advantages to using WirelessHART. "A plant shutdown is normally not required since the devices can be upgraded individually; however, the instrument may be offline for a short time during the instrument commissioning process. The existing wiring in the marshalling area is not affected, so during and after installation of the WirelessHART Adapters, the plant should continue to operate. There is normally enough space to mount the WirelessHART adapter on or near the field instrument, so installation is relatively easy. A HART Multiplexer requires control room cabinet space. This premium area is normally occupied with other existing hardware. As a result, the costs of an additional cabinet or junction box must be considered."
New Features in HART 7
HART 7, the first major upgrade of the HART Communication Protocol since 2001, includes significant new features and upgrades over HART 5 and HART 6. Bob Karschnia, Emerson Process Management's vice president of wireless, describes them. "HART 7 is an evolutionary step in HART technology that continues the tradition of adapting to changes in instrumentation design," he says.
"HART 7 now allows eight variables to be communicated in a single message reflecting the trend for more multivariable devices that do calculations, as well as making measurements or actuating a valve," continues Karschnia. "As the importance of these additional variables has become evident, HART 7 now provides status indications for each one. To further support the multiple values provided by these products, the user can now simulate each variable providing the ability to do a "loop check" on both the analog and digitally communicated values. Data is now time-stamped. Although the wired devices may not have a real-time clock, they can still provide a relative time and eventually the control systems will become capable of synchronizing time across the wired HART devices, which will allow a much more accurate picture of plant performance. In the same way, system enhancements for HART 7 will be able to take advantage of condition-based reporting (report by exception), alert acknowledgement, data trending and other features that will appear in the HART devices."
As Steve Todd, vice president of sales and marketing for Moore Industries-International, reports, "We anticipate HART being used more frequently in multidrop applications. Devices such as our TCM Multichannel Temperature Concentrator System have multiple channels and can have multiple devices on a single line. Devices like this take full advantage of the new features found in HART 7. The squawk-and-find device features will be very useful for configuring devices in multi-drop applications. The new sub-device feature will also be useful on our multichannel devices so that their internal data can be more logically organized. Exception-based reporting will improve the responsiveness of multidrop applications by reducing the data that must be transferred."
And of course, HART 7 includes WirelessHART.
The WirelessHART Standard
WirelessHART has already been used in a number of applications that would be difficult, if not impossible to do with wired HART. BP has expanded its Cherry Point refinery applications, installed Emerson's WirelessHART network throughout the tank farm in its R&D facility in Naperville, Ill., U.S., and is making installations at its other refineries around the world.
BP Cherry Point is a 225,000-bpd refinery located in northwestern Washington State in the U.S., and is the largest supplier of calcined coke to the aluminum industry. One out of every six aluminum cans is made using BP Cherry Point's calcined coke.
WirelessHART-enabled Smart Wireless transmitters on the refinery's calciner unit monitor bearing and calciner coke temperatures to help prevent fan and conveyor failure. Fans can cost up to $100,000 to repair, but more important, can be down for up to 10 days with associated production losses. The 15-transmitter wireless installation, originally done in 2006, continues to run reliably while eliminating operator rounds in the field.
Endress+Hauser has engineered a robust WirelessHART network that reliably communicates with 44 WirelessHART adapters and two Fieldgate gateways to adapt magnetic flow meters and pressure transmitters spread linearly over 2400-foot-wide leach field sections. These leach fields are regularly relocated, and the flexible WirelessHART redundant and mesh architecture accommodates the relocation with a minimum of effort.
Siemens, ABB and other vendors have also installed WirelessHART projects. It is estimated that there are already over 1400 installed WirelessHART-enabled field devices in the world.
MACTek has done one of the most innovative projects with WirelessHART to date, at Progress Energy in Crystal River, Fla. Dick Fletcher, of Progress Energy, says, "Our Performance Testing group needed a new data acquisition system. The data acquisition system needs to collect data from a variety of pressure and temperature transmitters. In addition, the system needs to be portable and flexible enough to operate with a constantly changing number of instruments and scan rates. The system needed to be portable, able to handle a variety of instruments (typically high-accuracy pressure and temperature transmitters), be easily configured, as every test is a different configuration, and interface with standard commercial instruments using standard protocols. In the long term, we wanted to broaden the scope of the data acquisition system from being simply for thermal performance testing to also include other testing, such as dye dilution flow testing and equipment diagnostics, and make the real-time test data available upon the corporate wide-area network."