"There is just a difference in philosophy of how the systems work," says Ladd. "We're using mesh networking, where all of the devices are routers. We're using 802.15.4 radios, and that is the same radios ZigBee [ZigBee Alliance, San Ramon, CA] uses. We added the frequency-hopping technology, additional security measures, and a number of things that will make the WirelessHART network much more robust and backward compatible to 26 million devices already installed."

Foundation Fieldbus and Profibus are two organizations that build their communications protocols on top of either ISA 100.11a or WirelessHART. "To the extent they have simple networks, then WirelessHART could serve as a base for Foundation Fieldbus. But to the extent that their customers want to do more like control any of the field devices, then they will find that the additional flexibility of ISA 100.11a will allow their networks to work better for control reasons," predicts Caro. "Profibus appears to be less interested in the additional security and the other requirements that are given by ISA100 and appears to be leaning toward founding the wireless version of Profibus on top of the WirelessHART protocol. That of course could change as the users of Profibus change. For example, Profibus is largely influenced by the German chemical industry, which is the largest industrial category in Germany and includes companies such as Bayer. To the extent that Bayer recognizes the additional reliability and security added by ISA, it could change the product specifications that are currently occurring within the Profibus organization. But since our standard is not yet complete, there is no basis for them to do that at this point."

Collaborations

On the same day, ISA announced that HCF and ISA had collaborated to "develop a single wireless standard for process measurement and control applications." According to this statement, each organization had granted copyright license to the other such that HCF would have access to ISA100 documents at all stages of development and ISA would have access to HART protocol specification, including WirelessHART. ISA announced the formation of a joint technical committee "to assess WirelessHART technology for meeting ISA objectives and recommend possibilities for incorporation into the ISA100 family of standards." Whether the incorporation of WirelessHART into ISA standards will or can actually take place remains to be seen.

Says Caro, "For a long time, I have been a very strong advocate of trying to get the WirelessHART group to abandon what they have done and simply use those parts of ISA 100 that appear most like WirelessHART. That could be done without real technical compromise, but they seem to be unwilling to do that. We have an investigation to look at WirelessHART and make it a proper subset of ISA100, but that doesn't seem to be happening."

According to Ladd, "WirelessHART is not going away. WirelessHART incorporation into ISA 100 is up to ISA at this point. We have talked about it. There was a ballot posted on the SP 100 website to begin a WirelessHART subcommittee, so there are things definitely moving forward to incorporate WirelessHART into SP100."

"[In April], there was a motion raised within SP 100 to make WirelessHART as it exists, with no changes, an SP 100 standard, and I think that will be approved," says Karschnia. "If it doesn't, you end up having competing standards that are in the industry and that will be an issue because it will just confuse customers and less people will buy in general."

So is it political? "I don't know," says Caro, "It's more economic. And it's not economic in serving the end user, it is economic in serving the customers of the HART Communications Foundation who are the vendors."