Which Way Wireless?

ISA100.11a and WirelessHART – Your Future Wireless

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To minimize the latency of a mesh network, ISA100.11a is being written to allow configuration of a field backbone into the network. WirelessHART does not specify such a backbone network. The HART Communication Foundation states that it designed WirelessHART without a field backbone to permit it to be used with any commercially available backbone such as Foundation Fieldbus HSE, Profibus, Profinet, WiFi, etc, in much the same way that ISA100.11a, which is itself designed without a backbone, can be used with commercial backbones.

Option 3 certainly is one way to gain a single standard, which end users clearly want, based on all the research that has to date been done. However, since there is no work on this for the current draft of the ISA100.11a standard, it is unlikely that this will happen any time soon. It also seems clear that the earlier availability of WirelessHART devices may make this option unnecessary.

The purpose of Option 3 in integrating these protocols is to allow suppliers to build field devices that will be capable of operating in either a network configured to meet only the “original WirelessHART specifications,” or in a more general ISA100.11a network. Therefore, devices requiring the protocol splitter will only be required for installation in plant areas in which there are devices that are NOT capable of using ISA100.11a protocol (do not contain the dual-protocol stack.) This means that the merged protocol is only necessary only to support installations of new devices in wireless network segments that were originally constructed to use only the WirelessHART protocol.

Clearly, Option 4 is the one for which most end users wish. There are two problems with this option: it will take time to produce – more time than any other option; and it does not seem to solve the market dilemma in which there will be two incompatible product families being sold until the vendors support the unified standard, if they ever do. The only problem option 4 resolves is the end user dilemma.

Will there be a significant number of those purely WirelessHART networks to require merged protocols within the ISA100.11a standard? Almost certainly. Emerson has already sold significant numbers of SmartWireless devices that are extremely similar to WirelessHART, and that the company has pledged to convert to WirelessHART products. The WirelessHART version of the device that attaches to the 4-20ma wiring for an existing HART transmitter is called a “thumb” by Emerson/Rosemount who has already announced that it is currently taking orders with a shipping date in early May.

No supplier has yet made an announcement for an ISA100.11a equivalent device, but such products are likely to appear before the end of 2008 or in early 2009. This apparent time gap is driving all but one of the major automation vendors to build product to support WirelessHART without a corresponding commitment to support ISA100.11a.

If the promised launch of WirelessHART devices occurs in mid-2008 and those products are actually shipped later in 2008 in any quantity, then there may be hundreds to thousands of these devices installed. However, companies supporting ISA100.11a may not be ready to relinquish the market to WirelessHART. If, however unlikely this may seem based on the schedule issues necessary to develop a real issued standard, vendors release “pre-ISA100.11a” devices with a pledge to convert to compliant ISA100.11a in the future in mid-2008 and actually ship them later in 2008, there could be a reduced demand for pure WirelessHART devices.

We know that ISA100.11a can be configured to accomplish many of the WirelessHART functions, using a very similar application interface based on EDDL. Furthermore, the host network interface for both protocols will be the same. It also appears that there is little to no cost difference to support either protocol, but the cost of supporting two protocols is quite large for both vendors and users.  Furthermore, vendors may at any time choose to support both WirelessHART and ISA100.11a protocols by instantiating the required protocol stack in a number of vendor-specific ways, such as downloading or activation if previously installed. Given that there will be little functional or selling price differential is it worth the effort to integrate these standards? Is it worth it for vendors to support both standards?

Conclusions

Will the effort to create a dual-protocol stack standard actually occur? Will it really provide any value and will it be worth the cost?  It is certain that without strong end user pressure, the suppliers will not make any changes to WirelessHART with the result that some products will be installed in the field without the capability to ever be converted to ISA100.11a. Some users will buy WirelessHART because it will be available earlier than ISA100.11a instruments. Others will choose to wait for either devices that are ISA100.11a compliant, or are promised to be convertible to ISA100.11a. However, it is more likely that users will purchase neither in any quantity until the suppliers pick one standard or supply devices that can be configured or downloaded for either protocol. This confusion in the marketplace is just like HD DVD vs. Blue-Ray – users may decide to buy neither. The market always makes the “best” decision, not always the best technical decision.

Which “camp” will win this battle of the wireless protocols, sometimes called an “air-war?” The vendors seem to be aligned into these two camps, each with their own strategy. WirelessHART seems to have the support of device suppliers in the process automation space.  The support of device suppliers for ISA100.11a though is not yet clear.  Early adopter users must make a “bet” on their perception of the winner. Either way, if this division continues, the users will lose.

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