Bluetooth for industrial applications

12/03/2010


Dear Control Engineering:

I was listening to the recent Webcast about Wireless, and one of the presenters was talking about Bluetooth. How many different devices can use that without interfering with each other?

Fortunately, that Webcast is available for on-demand listening, so you can hear the presentation again if you like. Bluetooth is an interesting wireless protocol that uses IEEE802.15.1 radios and grew up in the consumer electronics space, but it is making inroads in industrial applications. One term that you hear in reference to it (and I think Ira Sharp from Phoenix Contact said it himself) is “cable replacement.” Bluetooth is used in applications that would normally have a short cable. It’s designed to cover limited amounts of data over a short distance. It’s not something you would ever use for heavy data backhaul across a plant. It is, by its nature, a point-to-point protocol. You don’t create Bluetooth networks in the way that you might with a protocol like ISA100.11a or WirelessHART. Two devices talk to each other, and that’s it.

If you think of one very common application, consider those odd cell phone buds. The wireless signal covers the same space that would normally be spanned with a cable. As I write this, I’m doing it on a wireless keyboard and with a wireless mouse that communicates with my laptop without a cable. Both of these devices communicate via Bluetooth.

Within our offices, we could easily have six or eight people all working within a 30 foot circle simultaneously using the same combination of wireless keyboards, but there is no interference. My keystrokes don’t show up on Elena’s computer, even though she’s four feet away and has the same kind of wireless keyboard. Each set of devices is matched and only communicates with its own set. This works because each device has its own MAC address, and as long as you have enough of these (it's a 48 bit address), they will not iterfere.

Bluetooth uses profiles that create the application layer for the protocol. For example, the Bluetooth specification says how a wireless ear bud should communicate with its host phone. That means you can buy a bud from one manufacturer and a phone from somebody else. In industrial applications, it can be used where you would normally use an RS-232, RS-485, parallel sensor, 4-20 mA, other analog signals, USB, and any number of other protocols over a short distance. Compared to other wireless protocols, it’s very fast, so you aren’t likely to see any difference in response time.

For industrial environments, Bluetooth can be used in intermittent walk-around applications, or where it is both permanent and continuous. For example, let’s say you have a device on the end of a robot arm that has to communicate with the controller on a continuous basis. You can eliminate that cable and its associated maintenance. Or, let’s say you have cabinets around the plant with PLCs or other controllers, and you need to talk to those from time to time. Using a walk-around communicator, you can link to the PLC via wireless and not have to open the cabinet, avoiding problems with arc-flash restrictions and the like. With industrial Bluetooth devices, you can configure the communicator so it will talk to whatever specific device you need at that given time.

Also read From consumer electronics to your HMI

--Peter Welander, pwelander@cfemedia.com



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