Which Way Wireless?

ISA100.11a and WirelessHART – Your Future Wireless

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By Dick Caro, CMC Associates, Acton, MA

There are plenty of wireless instruments for process automation available today, but they are all proprietary, do not conform to any standard, and generally are not interoperable. Each network constructed from these instruments generally uses a standards-based interface to the host system using OPC, Modbus, or similar protocols. Users would generally like to see a more integrated approach for host systems, but vendors tend to use such open protocols for connection capability to almost any host.

ISA100.11a is the name of the first standard being developed by the ISA SP-100 standards committee. The committee was officially chartered in 2005, with an editing team created in early 2007 to actually write the standard. Completion of the standard’s first draft is scheduled for November 2008, and it may be that this schedule will be met.

ISA100.11a is being targeted to serve the data acquisition and limited control needs of the process industries for this first release. Products designed to this specification are expected on the market shortly before the end of 2008 at the earliest, with compliance certified products available shortly after release of the standard in 2009.

Like all the HART specifications before it, WirelessHART is targeted to serve the data acquisition and control needs of the process industry. HART 7.0 planning began in early 2005, the specification containing WirelessHART was approved by HCF members in June 2007 and released by the HCF Board of Directors in September 2007. Among other capabilities, WirelessHART provides a new wireless communications path to capture the digital data contained in more than 26 million currently installed HART instruments without a direct digital connection to their control system. Products designed to the official HART 7.0 specification have been informally announced for sale and shipment, and compliance certified products are likely to be on the market by Third Quarter 2008, or sooner. At least one company has announced an OEM kit for other vendors to assist them in producing their own WirelessHART products.

Most observers question why there are two competing wireless standards for the same small industry. Many users involved in the development of ISA100.11a are questioning why these two very similar standards that are both based on the same radio (IEEE 802.15.4:2006) operating at the same frequencies cannot be united into one standard. These are excellent questions and deserve an answer that we will try to provide here.

The two standards are the result of the free-market. In November 2004, HART Communication Foundation (HCF) members explored the synergy of extending the HART protocol to enable wireless process measurement and control devices based on emerging wireless technologies (IEEE 802.15.4 and sensor mesh networking). HCF members endorsed the establishment of a Working Group to investigate and develop the appropriate extensions to the HART Protocol standards for wireless communication.  The new HART 7.0 standard including WirelessHART resulted from this effort and is a natural evolutionary enhancement to the HART Communication technology.  The HART 7.0 specification was produced by a small, focused, and dedicated group that was able to move much faster than the ISA 100 committee considering the vastly stated broader scope and purpose of ISA100. The HART 7.0 standard has been reviewed and approved by the 200+ members of the HART Communication Foundation, who are the largest group of vendors who manufacture field devices so it is well supported by process automation suppliers.

Interestingly, enough, many of the companies that supplied people to work on the HART 7.0 standard are the same companies that are also working on the ISA100.11a standard. The two standards are targeted at the same process applications, but are basically incompatible.  WirelessHART is an extension to the proven, well established and well supported HART Communication Protocol standard.  ISA100.11a is working to define an entirely new communication protocol targeted at the same process measurement and control applications. The HART Communication Foundation is primarily a vendor organization, and most of the people writing the ISA100.11a standard also work for the same vendors that are members of that Foundation. This is confusing for end users and causes them to wonder why these same vendors cannot cooperate with themselves.

Many end users and some suppliers have questioned the haste in producing a draft ISA100.11a standard that has not integrated the WirelessHART protocol. They also have questioned the value of the ISA100.11a standard when the WirelessHART standard is already available. As with the previous questions, these too are valid alternatives and should be examined. First, the haste in producing the ISA standard comes from the ISA’s sense of competition from WirelessHART itself and the general desire to complete a comprehensive work, once begun, as soon as possible.

ISA100 and HART Joint Analysis Team

The question remains: why can’t the WirelessHART specifications just be embedded into ISA100.11a? There are a number of reasons, mostly technical, but the main reason is that the HCF did not offer the wireless technology embedded in the HART 7.0 standard to be used in the ISA100.11a standard until the HART 7.0 standard was completed and released for publication by the HCF Board of Directors. Unfortunately, this was well after the writing of ISA100.11a had begun. Immediately following publication, the HART Communication Foundation provided ISA with the complete HART 7.0 standard to evaluate and consider for incorporation into the ISA100 standards including the offer of user rights should ISA want to adopt the WirelessHART portion of the specification. 

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