But what happens if you have a control system that doesn’t accept HART data or you don’t have room in your marshalling cabinets to install HART Interface Modules? What happens if it just plain costs too much money, and you can’t make the justify the project, even though you know you will save time, save money, and provide better performance to the plant—but you just can’t prove it in advance?
And what happens if some of the measurements you need aren’t from traditional process sensors at all—say from alarm switches on safety showers or gas detectors that would never have been interfaced with the DCS or other control system?
The HART Communication Foundation realized that there was a need for more than one way to connect data from HART devices to control and operations systems. So as an integral part of the HART 7 release, it created WirelessHARTTM. WirelessHARTTM is the only wireless communication protocol that is designed to work seamlessly and completely integrate with an industrial wired protocol.
So when do you use WirelessHARTTM? WirelessHARTTM is useful for hard-to-reach locations. It is great for doing process efficiency calculations, not just process monitoring and control. You certainly can use WirelessHARTTM sensors for control applications. Control columnist and Emerson Process Management consultant Greg McMillan wrote recently, “With the wireless PID algorithm, a comprehensive battery life management approach, exception reporting and a secure, reliable self-organizing and optimizing network, wireless process control is ready for all but the fastest processes, provided the transmitter resolution settings are right for the application. Use of wired devices will be relegated to processes requiring scan and PID execution times much faster than once per second, such as compressor surge and pressure control."
WirelessHARTTM can allow process operations personnel to place transmitters where they could never afford to place a wired device before. They can now use WirelessHARTTM devices to monitor secondary variables that can help optimize the process but that previously were impossible to measure in a cost-effective way. Maintenance personnel can monitor rotating machinery where it was not feasible without wireless sensors. Environmental monitoring personnel can measure health and safety tools, such as safety showers and gas detectors…even gas detectors carried on the person. Steam traps, water discharge, stack emissions, relief valve fugitive emissions and many other parameters and devices can be monitored in an extremely cost-effective way, using WirelessHARTTM sensors and devices.
This is why it is such a valuable feature of the HART 7 Protocol that the same information and the same programming and the same types of devices are available—wired or wireless.
For those who have wired devices and don’t have the ability to put in HART multiplexers or interface modules because of cost or space constraints, WirelessHARTTM adapters provide a simple, easy and cost-effective way to get the stranded data out of existing HART devices and into the control and information systems of the plant.
Interfacing with Other Systems
Another major advantage of using HART 7 and WirelessHARTTM is the large number of industry standard protocols the HART Protocol is designed to interface directly with: Ethernet (IP-based networks), Modbus TCPIP/RTU, OPC, FOUNDATION Fieldbus HSE, Profibus DP/ProfiNet, PLC/Controller Gateway, Serial (RS232/RS485), HART/485.
The HART data can be converted by industry-standard OPC server technology and imported into any OPC-compliant control system, data historian or database.
In addition, the Wireless Cooperation Team, formed of delegates from the Fieldbus Foundation and the Profibus Technical Organization, has been working for more than a year now to produce an interface specification for a gateway between WirelessHARTTMand FOUNDATION fieldbus communication technologies; an interface specification for a gateway between WirelessHARTTM and Profibus DP and Profinet communication technologies; and a common set of compliance guidelines for incorporation into the respective product registration procedures. This will mean that end users will have the ability to use any of the three most commonly found communication protocols without worrying about compatibility or interoperability issues.
Improve the bottom line
Plant optimization, advanced process control and predictive and prescriptive maintenance programs have been shown for years to contribute directly to the bottom line. Yet it has been expensive, in some cases prohibitively so, to instrument the process well enough to apply those techniques in the plant. HART 7 and WirelessHARTTM have broken that barrier and liberated all the data in the plant.