WirelessHART Logo from HART Foundation

For some time now, there has been a lot of discussion about WirelessHART (IEC 62591) and ISA100.11a standards.  This battle appears to be shaping up as the old Beta versus VHS and Blu-Ray versus HD-DVD.  Both are good technologies and both are a marked improvement in process control.  Of course, when it comes to new technology, there always seems to be a lot of debate and one prevailing standards wants to win.  There are really two companies, Emerson and Honeywell, which are leading the battle.  Everyone is waiting to see what happens.

It is important to first understand what is needed for a wireless communication network.  As with your home network you need a gateway or a router that “hosts” devices.  Then, of course, you will need devices.  These can be both wired and wireless.  For the purposes of this discussion, theses terms will be used.  It is important to note a distinction between process devices and network devices.

The basic difference between the IEC and ISA standards are the communication protocols they use.  Wireless HART uses the 802.15 allows for the networking of all devices.  This is generally referred to as a mesh network.  Rather than a traditional host-client relationship, WirelessHART devices will talk to both the gateway and other devices.  If a process device looses communication with the gateway, the information is routed through other process devices.  This creates reliability in the network.

The IEC standard uses the traditional 802.11 (Wi-Fi) protocol.  It’s like creating a Hot Spot in your plant.  This means that any device that is Wi-Fi (laptops, iPads, surveillance cameras) will work on this network.  When it comes to deployment ISA100 devices can be installed existing networks throughout the plant.  Reliability is achieved through multiple gateways, rather than multiple devices, as gateways can also be configured in traditional “master/slave” settings.

I am a proponent of using both.  Frankly, current communications in a plant are done through two different systems.  Control systems reside on one system and operations exists on another.  Each system can communication with the other but have an independent job.  This practice should continue with wireless technology.

WirelessHART only allows for instrumentation and process control devices to be a part of the network.  This information can be sent to a control system or asset management software.  This practice also keeps the frequency clear for process data.

ISA100 can then be used for the balance of the wireless network.  This would allow for personnel tracking, wireless cameras, laptops and a whole host of other network devices that benefit your plant.

In a way its the best of both worlds.

UPDATE:  Please note the comments below from Herman.  The ISA100.11 specification does allow for a mesh network.

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2 Responses to WirelessHART versus ISA100.11

  1. Herman Storey says:

    Your article starts out with a good analogy about VHS and Beta, then when you get into the details you manage to get the facts mixed up.

    ISA100 does embrace multiple radio technologies including 802.11 and 802.15.4. ISA100.11a is specifically a 802.15.4 based standard that does the same function in much the same way as WirelessHART. Standards that also use the same radio chips include ZigBee and WIA-PA (Chinese standard).

    All 4 of these communication standards provide for mesh network communication in the unlicensed 2.4 gHz ISM band and are intended to coexist with other users of that band (up to a point). They are built so they can share common radio chips and provide much of the same functionality. Like VHS and Beta, having multiple choices does not always add value.

    Like VHS and Beta these specifications are based on old versions of IEEE 802.15.4 and do not make use of new features in later versions of the IEEE standard. Refreshes in technology will happen and migration of technology is not as well covered in the current standards as I would like.

    I think we can do a bette job of developing compatible standards than we did in this case. We need to save diversity in design for places where the diversity can add value. I hope we can converge some of these radio technologies in the future, but convergence may not happen as quickly as would be best for our industry.

    Herman Storey
    Co-Chair ISA100

    • Herman: Thank you for your comment. When I originally published this, there was a lot of misinformation floating around. Unfortunately, it made its way into my post. I appreciate you taking the time to correct it.

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