It's Not Easy Being Blue

Bluetooth Has a Straightforward Infrastructure, Adapts to Frequency-Hopping, Copes Well With Interference and Is More Agile Than ZigBee

By Loren Shaum

Well-known in consumer electronics, Bluetooth is a relative stranger to machine builders. In the past several years, it has become a wireless standard for short-distance consumer communications, but is it suitable for machine automation?

Bluetooth was the code name of the Bluetooth Special Interest Group (SIG) when it was founded in 1998. The name comes from 10th Century Danish King Harald Blatand (Bluetooth in English), who united warring factions in Norway, Sweden, and Denmark — just as Bluetooth technology aids collaboration between devices in the computing, mobile phone, medical, and other industries.

Bluetooth is most famous for wirelessly connecting headsets and mobile phones, but it's also used to connect other devices, including digital cameras, laptops, PCs, and game consoles. Its chips use radio signals to transfer information over short distances (typically less than 100 ft).

Bluetooth 2.0 is the current version in most devices, and can transfer information that requires low-to-moderate bandwidth — up to about 3 Mbps — slightly higher than average broadband speeds, and has relatively low power consumption.

"Bluetooth is an excellent technology and is well-suited for those applications for which the standard provides profiles," says industry consultant Dick Caro of CMC Associates. "It wasn't designed for industrial control." Bluetooth was used briefly by Crossbow Technology. "However, Crossbow switched  from Bluetooth to technology based on IEEE 802.15.4 radios — the same used for ZigBee."

Caro co-chairs ISA's SP100 Standards Subcommittee working on wireless automation standards. The committee also selected the IEEE 802.15.4 radios, but with a more appropriate industrial automation protocol. "I don't believe Bluetooth really stands a chance in industrial automation," states Caro. However, he acknowledges that, with modifications, Bluetooth might be usable in some applications.

Nick Hunn, CTO of Ezurio, says the Crossbow switchover won't inhibit others from deploying Bluetooth in factory automation. Ezurio and other firms, such as ConnectBlue and Bluegiga, offer Bluetooth for medical machine monitoring.

"Look how long it took to get Ethernet adopted," argues Hunn. "Bluetooth has a straightforward infrastructure, adapts to frequency-hopping, copes well with interference, and is more agile than ZigBee. Its small size and low power consumption is ideal for non-critical monitoring. It's all about removing wires." Hunn adds that Bluetooth could reduce cabling and increase reliability in high-duty-cycle robot monitoring applications.

Phoenix Contact was the first major supplier to embrace Bluetooth technology for factory automation. It implemented Bluetooth in serial communication devices (RS232/422/485) and wireless I/O. "Bluetooth technology is appropriate and rugged enough for some industrial applications," says Patrick McCurdy, product manager. "Based on the IEEE 802.15.1 standard, Bluetooth was developed for short-distance, point-to-point applications, and has been adapted for small-point to multipoint personal area networks (PAN). The underlying RF principles are frequency-hopping, spread-spectrum (FHSS) that hops on 79 frequencies in the 2.4 GHz unlicensed band. It also has a high tolerance for electromagnetic interference (EMI) from motor drives, high-voltage lines, and other sources."

McCurdy argues that Bluetooth is well-suited for short-range (less than 300 ft) automation communications, temporary programming, and diagnostic connections. In one manufacturing cell, Bluetooth is used as a wireless connection between a robot and controller, says McCurdy. It can also replace slip rings and drag chains, in which hardwiring frequently needs to be replaced.

"Bluetooth also can access restricted areas for diagnostic monitoring or programming applications," adds McCurdy. "Control or electrical distribution cabinets are sometimes restricted from being opened without shutting down the machine., and requiring special equipment and training. With a wireless connection, you can access the equipment without being physically connected."