Virtual panel discussion – ISA 100 and WirelessHART

February 14th, 2014, Published in Articles: EngineerIT


by Hans van de Groenendaal, EngineerIT

Currently there are two industrial wireless communication standards, ISA 100 and WirelessHART with varying support for each one. There have been efforts to develop a common standard but some believe that newer versions of ISA 100 obviate the need for WirelessHART. Recently Tim Bourke, Honeywell Analytics, UK said in a White Paper that SA100.11a offers a more powerful and comprehensive architecture which provides all the benefits of WirelessHART and more, therefore obviating the need for WirelessHART.

We invited a number of industry experts to share their opinion on ISA 100 and Wireless HART and whether therey should be only one standard. Their differing opinions make interesting reading.

In our first discussion point we asked the participants for their opinion of the basic difference between WirelessHART and ISA100; and whether the applications are industry-specific?

Gary-Friend1 panel-discussion-kevin
Gary Friend, Extech
Safety Systems.
Kevin Preston,
Phoenix Contact.

Gary Friend, sales director, Extech Safety Systems said that WirelessHART is simply a way of extending HART capability using wireless technology. It gets more data from field devices compared to traditional 4-20 mA devices. It builds on the increased adoption of traditional HART in the industry which has been viewed as easier as and cheaper than adopting Foundation Fieldbus H1 or ProfibusPA. “ISA100 is open and not protocol specific and in my opinion has more scope. But it really comes down to DCS/PLC supplier preference as they have their strengths and preferences. It does not make sense to ask a vendor to implement a technology where their strengths lie with different technology”

Kevin Preston, business unit manager – interface & I/O networks, Phoenix Contact: “The major differences between WirelessHART (IEC62591-1) and ANSI/ISA100.11a-2011 can be directly attributed to the differences in each of the standards. Wireless HART is designed to address key end users concerns, which include security, reliability and appropriate fit and purpose to specific instruments in the field. ISA100 is designed to provide flexibility and in most cases is vendor specific, meaning that these systems are not interoperable. This may cause confusion at the end user level.”

Johan (Wessie) van der Westhuizen, product specialist – flow, pressure, temperature & wireless networks, Yokogawa: “The basic difference is the protocol used in the two. WirelessHART is limited

wessie-20140206_090738 panel-discussion-Maharaj-VineshIMG-3918
Johan (Wessie) van der Westhuizen, Yokogawa. Vinesh Maharaj, SAIMC.

to only HART protocol, while ISA100 can accept all the different protocols like HART, FF and Profibus.”

Vinesh Maharaj, president, SAIMC: “WirelessHART is the evolution of an old tried and tested technology from cable to wireless, while ISA 100 is a paradigm shift in the adoption of a new technology that fulfils a particular need in the industry. ISA100 was developed from basic, modern principles and therefore is much more flexible from a configuration point of view, it is more energy efficient (battery life) and has virtually no device limitations due to the open IPV6 standard.”

Selvan Murugan, associate, Royal HaskoningDHV: “The fundamental difference between the two standards is, in my opinion, the objective of their creation. WirelessHART was purposefully developed by the HART Communications Foundation in order to enable field instrumentation with HART communication capability to interface wirelessly with an automation system. ISA100, on the other hand, was purposefully developed by the International Society of Automation to support a wide range of wireless industrial plant needs,

itech_Selvan-Murugan panel-discussion-lita-IMG_9200-
Selvan Murugan, Royal HaskoningDHV. Lita Mpahlwa, Endress+Hauser.

including process automation, factory automation and RFID. The application of either standard is not industry specific (but more application specific) as wireless applications can be found in a wide range of process and manufacturing environments.”

Lita Mpahlwa, project manager, solutions projects, Endress+Hauser agrees that WirelessHART is an extension of an existing protocol, HART, with the introduction of new devices to enable wireless communication of process sensors – it is more of an evolution. “ISA100 is not protocol specific, but also enables wireless communication at sensor level – merely a radical piece of technology.”

In the second discussion point we asked the panellist to comment on their preference and the reasoning that informed their preference.

Kevin Preston: “Based on experience in the field; ISA100 systems are far easier to implement for basic I/O applications and have a wider application base. WirelessHART on the other hand is limited to petro-chemical applications and in most cases requires skilled staff to configure the required network. Apprehension to the use of wireless signals for control in the petro-chemical industry is still very high, so implementation is very limited.”

Selvan Murugan: “Applications up to now have only required monitoring and control of field instrumentation; hence WirelessHART is my preference for this application. WirelessHART is supported by the leading suppliers of field devices i.e. ABB, Emerson, Endress+Hauser, Pepperl+Fuchs and Siemens so there is no associated technology risk. These organisations have invested heavily into making the technology simple and easy to interface to the automation systems for the basic plant requirement. There are also benefits to be realised in terms of, engineering support, and availability of spares. Once wireless pervades the automation space and broader applications require enhanced interoperability between systems and devices not traditionally networked, ISA 100.11a becomes a consideration (obviously dependent on local, South Africa vendor support).”

Gary Friend: “It really depends on what you want to achieve. As always it would be easier for everyone if there was one standard in true sense of the word. For me ISA100 has more scope longer term.”

Lita Mpahlwa has a definite preference: “WirelessHAR is based on a well-established old technology HART. This makes it relatively easier to accept and understand especially when it comes to implementation.”

Vinesh Maharaj is an ISA 100 man. “ISA100 is an open, modern standard that even allows WirelessHART to route through it. ISA100 provides configurable time slots whilst WirelessHART only specifies a 10-ms time slot. There are configurable channel-hopping mechanisms in ISA100 whereas WirelessHART specifies only one channel-hopping mechanism. ISA100 has options to enable/disable security settings however, WirelessHART dictates that security must always be on. Devices in ISA100 do not have to support routing whilst WirelessHART devices, must support routing. Backbone routing allows for greater bandwidth and for added flexibility ISA100 does not specify what the backbone network is; it could be any high data rate network including wireless or wired Ethernet. Hence ISA100 is a better overall value proposition and is future proof when compared to WirelessHART!”

Wessie van der Westhuizen: “I think there is a place for both wireless systems, although I prefer the ISA100, because of its flexibility.”

Because ISA100 is a family of standards do you believe that it will ultimately offer more flexibility to accommodate newer applications?

Vinesh Maharaj says yes. “ISA100 is not locked into an old protocol stack and founded on old technology. The ISA100 implementation of the OSI stack enables it to continually evolve as technology evolves. ISA100 can currently support all established industrial protocols, whilst WirelessHart is not able. This is a sign of the future.”

Selvan Murugan: “ISA 100.11a already features native flexibility, and I do believe that it will provide the base architecture and interfaces for newer applications, whilst WirelessHART will be confined to the field level. ISA 100.11a was developed with flexibility, support for multiple protocols, use of open standards, and support for multiple applications as strict design criteria (which the standard has met).”

Kevin Preston: “I do believe that with the development, acceptance and reliability of the ISA 100 systems in the market, there will undoubtedly be newer applications for these systems.”

Lita Mpahlwa admits that ISA 100 can accommodate newer applications but warns that even though with flexibility there can be complexity. “Decisions would need to be made with extreme caution.”

Wessie van der Westhuizen: ”There are daily new developments to improve ISA100 and to accommodate new and difficult applications.”

Architecturally the standards have many differences. WirelessHART extends HART by introducing device types; ISA100 introduces the concept of roles and allows these roles to be applied in various combinations. Do you believe that this different architectural approach favours ISA100 in becoming the more dominant standard?

Gary Friend: “It is hard to say, but I think WirelessHART is a quick win in the short term with reduced outlay. It will depend on what you are trying to do and which vendors you select to work with.”

Vinesh Maharaj: “Yes, role profiles give birth to flexible device configuration according to on site needs.”

Selvan Murugan: “The only benefit that I see with regards to the roles concepts in ISA 100.11a is that very large networks can be realised through the use of backbone routers. This is a great benefit but wireless networks in the automation space tend to be relatively small, confined due to propagation limitations. A drawback is that the ISA100.11a System Manager must also keep track of the roles that specific devices support, and it must be able to correctly provision and manage those devices. This makes the System Manager more complicated to use from a user perspective. In addition to this, ISA100.11a devices are not mandated to support the router role. For this reason it will be very likely to see ISA100.11a networks that are star-only vs. WirelessHART networks which are inherently mesh.”

Wessie van der Westhuizen: “In the end I think ISA100 will offer more choices to the customer and WirelessHART may be more than what is needed.

Kevin Preston: ”Yes. The ISA100 architecture offers a much more favourable approach, by offering a more flexible work platform.”

How important do you believe is the notion that industry should adopt one standard?

Gary Friend: “Ideally this would be great but different applications have different requirements (e.g. factory automation vs. process automation) and vendors have their own preferences and commercial interests to protect.”

Vinesh Maharaj: “I think it is very important in order to control costs of the end-users, provide greater stability of networks and interoperability. R&D spend that is complementary rather than competitive will also be more economical for the vendors. Standardisations objective is to provide and overall better solution at a lower cost.”

Wessie van der Westhuizen: “In this world there is a place for both standards”.

Selvan Murugan: “If you ask any automation professional, the words ‘long term view’ applies to automation architecture design and strategies, however, we should not take ourselves too seriously. Automation systems these days now have a life cycle of five to ten years as opposed to the 30-year life cycles that we are accustomed from legacy systems. As a result of this, I strongly support the notion that standards will change even quicker, new ‘standards’ will be developed faster to replace those that we know of. The Fieldbus ‘war’ did not yield a single Fieldbus standard, as was the desire – and they all exist today and are used by many automation professionals in many different applications. So, I therefore, strongly believe that the future will be a combination of well-designed wireless standards developed to support the various applications and devices. As far as the notion that the industry should support a single standard goes, I do not believe that this is a valuable use of time and resources.”

Lita Mpahlwa: “A uniform standard is beneficial to both supplier and user. The user has the ability choose from various suppliers and not be tied to one supplier or a few – this helps maintain a healthy competition in the market place. From the supplier’s perspective, if several suppliers conform to a single standard the development costs can be reduced.”

Kevin Preston: “From a standards point of view, this makes very good sense. This will also formalise the industry and proven suppliers.”

Can the two standards be merged into one or are the differences too great to achieve this?

Vinesh Maharaj: “Technically it should be possible, but the unfortunately the competing interests of the parties have hampered this for at least the past three years! At this point it appears that the WirelessHART standard is facing obsolescence as it can be accommodated by ISA100. Hence this may be one of the reasons merger is proving difficult as it will be a win-lose situation.”

Kevin Preston: “Again yes, this is possible, as both systems contain many similarities, unfortunately architecturally they are very different. Here standards will have to be discussed and agreed to.”

Wessie van der Westhuizen: “I believe it can be merged, but I don’t think this will be soon.”

Lita Mpahlwa: “Technically the two standards can be merged with great difficulty as they were designed to meet different objectives – the common objective would first need to be defined.”

Selvan Murugan: “The two standards cannot be merged into one due to the technical incompatibilities listed below (identified by the Convergence Working Group):

  • Time synchronisation: ISA 100 Wireless uses the IEEE 1588 method for distributed network time that is also used by IEEE 802.15.4e, the latest version of the personal area network standard. WirelessHART uses a fixed slot time interval of 10 ms and derives time from that base.
  • Slot time: While the ISA 100 Wireless protocol separates slot times from time synchronisation, allowing variable slot times, WirelessHART depends on a single slot time to support time synchronisation.
  • Meshing methods: WirelessHART uses a dynamic proprietary method to form mesh associations. ISA 100 Wireless also forms mesh associations dynamically in a proprietary way, including the formation of duocast links. WirelessHART supports redundant paths for the mesh, but does not transmit to the redundant node during the same slot time. The duocast method used by ISA 100 Wireless sends redundant messages to the primary node and the duocast node in the same slot time.
  • Network addressing: WirelessHART uses network addresses based on a unique number series originating with the HART Communications Foundation. The low-order 16 bits are in the device, while the high order 48 bits are in the gateway. ISA 100 Wireless is similar except that the number series originates with the IEEE Standards Registration Authority. In addition, ISA 100 Wireless fully supports internet protocol version 6 (IPv6) at the link layer.
  • Transport layer: WirelessHART created a unique transport layer to assure end-to-end delivery of messages. ISA 100 Wireless uses the internet-standard UDP method to assure end-to-end delivery of messages.

Unless all five of these differences are resolved, interoperability between ISA 100 Wireless and WirelessHART is not possible.”

Many thanks to the participants in our discussion – editor.


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