A matter of timing

As a member company of HCF, Emerson attributes the speedy approval of WirelessHART to the organization's size and approval process. HCF is a small organization comprising the major vendors and users of wireless devices. "It's consortium of companies and customers that have a vested interest in making something happen, so they tend to be more efficient at making things, and it shows up in a standard that goes to market much quicker," says Bob Karschnia, vice-president of Wireless, Emerson Process Management.

ISA is a worldwide standards-making body that operates under American National Standards Institute (ANSI) rules. Following ANSI rules means that the document must undergo several rounds of comments, resolution, and voting to become a US national standard and a cycle for becoming an international standard and approval through IEC. So far, the 100.11a prestandards document has undergone a round of comments and resolution, and, according to Caro, the final standards document is being drafted. "Right now, we are on schedule and the next seven months or so will be devoted to voting and comment resolution."

Designing a standard starts with conducting a number of "use cases." Use cases help determine whether prototypes can solve specific real-world industrial applications such as monitoring temperature in a tank or controlling the flow of steam into heating and cooling jackets. Both ISA and HCF have conducted use cases. According to Karschnia, HCF went through all of the use cases that had been developed for 100.11a. "We found that every one of them is met by WirelessHART."

Use cases differ from validated confirmation tests, which prove that an application meets an accepted standard. This is one difference between WirelessHART and ISA 100.11a. "As a matter of fact, WirelessHART is still preparing its confirmation test sweep," says Caro. "With ISA 100, the production of a validation sweep is going along in parallel with the standard. When the standard is issued, it will be just a few weeks afterward that the validation sweep is complete."

Ladd questions this approach. "You have to write the standard, then build to the standard, then test to the standard. How do you build a device to a standard that doesn't exist? To me, that doesn't make sense. Once the standard is complete, then you can begin to develop your product to validate the standard, you make modifications to the standard if you find discrepancies, that is part of continuous process improvement."

According to Caro, the intent for ISA 100 is that before the standard is published, a number of companies will have already used the draft standards document to build product, and therefore they will get the actual use of the standards document and will have a chance to make corrections to it during the comment period. "The HART organization has the freedom of being independent to choose to issue their standard without that kind of comment-resolution period, which they have done. That shortcuts the timing requirement, but it doesn't necessarily make the standard available for production devices any sooner because they will have to go through the next revision of their document. It is now HART 7.0. Before that standard is completed it will certainly be at the 7.1 phase, reflecting the comments of the companies who have tried to build products to that standard."

Ladd explains that HCF provides 60 days for review and comment and a 30–60 day resolution period before the board of directors vote on ratification of any member-approved changes.