Listen in: What are ZigBee and Bluetooth, and how can they help me?

The names are common, but do you know what they really describe?

06/19/2008


Walking the aisles of the Sensors Expo, there were many booths from companies that make wireless modules for ZigBee and Bluetooth . If you’re trying to work with wireless in an industrial environment, what should you know about these? Can they help you? ( Click here to hear comments on ZigBee from Bob Buczkiewicz, LS Research , and Pelle Svensson, connectBlue .)

The short answer is yes, but with some heavy qualification. First it will help to explain what these things are, starting with ZigBee. Stated in very simple and non-technical terms, ZigBee is a protocol that works with the IEEE 802.15.4 radio. It supports networking from device to device using several different protocols including point to point or mesh. However it isn’t complete. Using a crude analogy, think of a hamburger with a bottom bun, a patty, and top bun. The 802.15.4 radio is the bottom bun. ZigBee provides the patty. That’s most of the sandwich, but you still need the top bun, or in this case the application providing system functions. The top bun, the application layer, is is not included in the ZigBee layer, so most companies end up writing their own instructions.

Put in process instrumentation terms, that top layer is what takes information from a sensor and packages it so the infrastructure can send it to the gateway so your distributed control system (DCS) can read it. The lower layers provide the infrastructure. The problem is that if a company writes a proprietary top layer, it will only operate with other devices using the same system even if the other layers are the same. That’s why two ZigBee-enabled devices from different companies may not interoperate.

Bluetooth is similar in that it is also a hamburger patty solution and has to have the top bun. However, it has striven for a higher level of interoperability. Bluetooth has profiles, which are basically pre-configured application layers. There are many of them that cover a wide variety of applications. One common example is those odd earpieces people use with cell phones. It’s easy to mix manufacturers for those because they all use the same headset profile.

ZigBee is working on compiling profiles as well, although it is not as far along in the process. As those become more common, making interoperable devices will be much easier. Of course that assumes you want interoperability. Some companies like proprietary platforms, even to the extent of creating their own hamburger patty layer as well. For example, Emerson’s Smart Wireless platform skips ZigBee completely and has its own solution for everything above the 802.15.4 layer. WirelessHART is the same way but has offered the protocol for many companies to use, creating its own interoperable platform, a standard guided by the HART Communication Foundation .

If the whole discussion leaves you with a headache, you’re not alone. Understanding the complexities of wireless protocols and trying to create interoperability requires careful analysis. As time goes on and equipment becomes more common, hopefully the number of protocols will coalesce around the most useful, or at least the most successful.

—Peter Welander, process industries editor, PWelander@cfemedia.com ,
Process Instrumentation & Sensors Monthly
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