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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