It has become obvious that industrial wireless is shaking off the uncertainties that plagued it for the last decade and is taking its place as a viable alternative to traditional copper-based communication technologies. For instance, Emerson Process Management recently announced its two billionth operational hour across its global installed base of Smart Wireless technology.
At the process instrumentation level this has been driven by rapid advances in the chipsets that support the ISA 100.11a and WirelessHART protocol standards, both of which are leading the evolution of industrial wireless networks in process automation. Most notably, the sensor suppliers now have a technology platform that enables mesh-based inherently redundant device level solutions that are able to interface to a plant-wide WLAN facility or backbone. And most importantly, they can now do this using only a fraction of the power that was previously required.
However, the fact that there are two standards out there is causing confusion among some end users and thus hampering adoption. This need not be the case if one considers some of the practicalities. For instance, at the physical layer both standards use IEEE 802.15.4-compatible DSSS radios operating in the 2,4 GHz ISM radio band. Both standards are also based on the idea of self-organising mesh network topologies. In fact, the self-organising mesh functionality is hard wired into the devices, and so independent of anything happening further uap the OSI stack.
This is not to say that there are no significant differences between the standards. There are certainly differences and, from an end user perspective, perhaps the most significant of these happens at the application layer.
In the case of WirelessHART the application is always WirelessHART based on the 7.0 release of the HART protocol. The ISA 100 standard is designed to support a wider range of plant needs and so there is more flexibility in terms of application definition. For instance, in addition to process automation, RFID and other factory devices can all coexist together in the ISA 100 network. (Incidentally, the application layer of an ISA 100 device can accommodate the HART profile, although reports indicate it may not be as efficient as that provided as part of WirelessHART.)
Architecturally there are many other differences, for instance in the way timeslots are proportioned, the channel hopping and other security mechanisms, as well as the routers and gateways required to support the different network architectures. In fact, there are routers and gateways available today that can support both of the standards. Admittedly the ones I know about do not provide simultaneous dual functionality, rather they are programmed prior to power-up and then boot themselves into the relevant configuration.
The point is that while there are differences, both are internationally accredited standards and both are ready for use today. For end users with primarily legacy HART instrumentation at their facility, WirelessHART may be the logical choice. For those wanting to extend their wireless architecture beyond pure process monitoring and control, the more flexible application layer of ISA 100 may be the better option.
Fieldbus wars are nothing new, in fact they have been around for decades, but that has not stopped end users from choosing between Profibus, Foundation Fieldbus, Modbus, LonWorks, Mechatrolink, EtherCAT or any of the other available types. To help clarify the problems associated with the dual wireless standard, check out the article by SAI&C’s contributing editor Andrew Ashton on page 76. We hope it helps you choose the right horse for your course.
Remember to look out next month for the ‘Technews Industry Guide – Wireless’ that will be posted free with the July issue of SA Instrumentation and Control. Just like last year, the 2014 edition will provide a one-stop resource that covers everything from low power wireless mesh sensor networks through the higher power WLAN devices used to establish the plantwide backhaul networks that transfer data to and from the process control system.
Scada Review 2014
It is the June issue again and so time to publish the 2014 SA Instrumentation and Control Scada Reviews. Andrew has done another fantastic job of collating this feature and notes in his introduction: “For readers, the value of scada reviews is not always about the capabilities of the scada product – it may be about how the project has been engineered or managed: risk mitigation, handover procedures, the application of particular standards or HMI design considerations.”
This year’s reviews contain insights into all of these and more, you will find them starting on page 28.
Steven Meyer
Editor: SA Instrumentation & Control
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version