01 May 2003
Bluetooth gets a filling
Leaders take a bite out of industrial misconceptions.
By Bill Drake
MD Totco knew what the problem was; they needed an easier solution. This manufacturer of offshore drilling rigs needed to transmit oil pond levels across a road to an oil-drilling rig programmable logic controller system. Then they thought of a solution: they should go wireless.
What is ISM Band?
The FCC and their counterparts outside of the U.S. have set aside bandwidth for unlicensed use in the so-called industrial, scientific, and medical (ISM) band. Spectrum in the vicinity of 2.4 gigahertz, in particular, is being made available worldwide. This presents a truly revolutionary opportunity to place convenient high-speed wireless capabilities in the hands of users around the globe.
Source: D-Link Corporation
Scenarios like this are typical of what companies can look forward to with industrial wireless technology. Getting wireless instrumentation for the manufacturing plant has been an elusive goal for some time. As electronics and data processing technology move forward, industrial instrumentation developers build finer tuned processes, better management information, and greater productivity and performance. Sensors, data acquisition equipment, programmable logic controllers, and process control computers traditionally needed a tangled web of networking technology and cabling to send the signals from source to destination. All these cables have installation and maintenance costs.
The dream is to replace the cables with wireless technology. In the case of MD Totco's wireless installation, "the temperatures ranged from 120ºF to 150ºF with 100% humidity; water and mud spray were everywhere," said MD Totco's Sean Cuff. "The units were about 50 feet apart, but the line of sight was not direct," he said. The transmitter was in the mud pond, and the receiver was on a platform across an access road and on the other side of the steel oil derrick. "The product worked as designed," Cuff said. "No condensation of buildup appeared inside the box." The team monitored pond level to evaluate the condition of the drill hole. Pond level fluctuations are indications of the drill strata, and the rapid change in level is an indication of problems in the drilling effort.
Designers intended the units to have DIN-rail mounting and 24 volts direct current power, providing four channels of 4–20 mA signaling from transmitter to receiver. Signal loss dry contacts alert the user to a link problem.
Before the realized dream of industrial wireless, three significant barriers deterred manufacturers from selecting wireless process and network signal equipment: cost, proprietary solutions, and security issues. Wireless technology costs surpassed cabling for all but the applications—where wireless was the only effective solution (as in rotating platforms). The proprietary nature of previous wireless solutions forced users to commit to a single supplier. Signal security, integrity, and robust performance were operational issues that concerned wireless users in a big way.
IN HOPS BLUETOOTH
Since then, Bluetooth wireless technology has adapted a U.S. military battlefield communications system—frequency hopping spread spectrum. The radios in Bluetooth hop randomly among 79 different frequencies at approximately 1,000 times per second—that is an incredible amount of security. Messages divide into small packets, sending one packet per hop. If the receiver is unable to correctly interpret the packet, it sends a message to the transmitter, which resends the message and reinserts it in the proper sequence. On top of the entire message structure, 128-bit encryption provides more security.
Frequency hopping also aids in robust operation. The chances of interference traipsing in on all frequencies are much smaller than on any individual frequency. Some of the frequencies will get through at all times. Because the packets retransmit as needed, all packets will get through. Bluetooth provides three radio options. You can use Class 3 operation in a PC space and get reliable signaling in a ten-meter radius. Class 2 operation will give you a mobile networking and office environment with a 25-meter radius. Class 3 Bluetooth operation is for enterprise operations such as the factory floor and provides 100-meter signaling.
Bluetooth operates in the frequency range of the 2.4-gigahertz industrial, scientific, and medical (ISM) band, which is available worldwide for user license-free equipment operation. Manufacturers must still certify equipment, making sure it meets technical requirements for operation in each jurisdiction. The universal applicability of this ISM band means lower costs for Bluetooth devices because manufacturers can build equipment in volume with no special variations for specific political jurisdictions.
EVERYONE CAN PLAY
Technology develops from simple, straightforward applications to more complex ones. Built-in Bluetooth in commercial off-the-shelf laptops, portable digital assistants (PDAs), and cell and standard inexpensive adapters for PCs allow inexpensive, standard devices to communicate with Bluetooth instrumentation without proprietary or custom test equipment. It is called non-proprietary interoperability. With it you can calibrate, test, and monitor without plugging in, opening loops, or mechanically connecting to instrumentation.
Industrial instrumentation manufacturers are responding to this opportunity by building Bluetooth-enabled devices, which bring these features to the factory floor. Some of the first products provide Bluetooth wireless secure cable replacement for instrumentation signals. Additional equipment is available to bring monitored signals into laptops and PDAs for monitoring. Other applications include using PDAs for setup and equipment calibration.
Wilcoxon Research introduced models with four 4–20 mA circuits from point to point. The application can replace cables in both outdoor and indoor environments.
Oceana Sensor introduced a model where Bluetooth monitors machinery performance. Diagnostics indicate performance using Bluetooth communications from the machine to the PDA or laptop that monitors the equipment. The model includes provisions for temperature monitoring, vibration monitoring, and other optional signals. Display software shows machine performance on Bluetooth equipped PDAs and laptops. The system allows the user to approach the machine equipped with diagnostics. Bluetooth connects with the PDA, then monitors the state of the machine's health.
Parker Hannifin implemented Bluetooth for machine configuration and control, process monitoring, mobile platform control, and monitor signaling. Pneumatic and electric actuation can take advantage of Bluetooth-enabled PDA and PC-based human machine interface for configuration and control. Menu-driven commands allow the user to start and stop the process and to set up the operations for speed and distance of operation. The user can coordinate with other actuation and monitoring equipment as it performs designated functions.
At the Hannover Fair, Parker demonstrated a complete motion control system. Pneumatic and vacuum devices on a rotating platform picked up parts, then manipulated, custom printed, and dispensed them. To control and monitor devices on the rotating assembly platform, operators use Bluetooth to eliminate the complication of wiring and slip-ring communications. Process signals include open/close, pressure, and temperature, which the system monitors through Bluetooth transmission.
While Bluetooth is less costly to implement, has better built-in security, and is more immune to interference because of its operating technique, it transmits data at about one tenth the speed of IEEE 802.11b. Yet for industrial instrumentation and control, this is not a critical factor. The product solutions above resulted in direct communications with transmission rates. That is more than satisfactory for the applications. In some cases, the manufacturers used the inherent smart capabilities of the Bluetooth device to preprocess data and reduce communications bandwidth requirements.
BLUETOOTH VS. IEEE 802.11B
But even with its sparkling veneer, is Bluetooth the answer to industrial wireless? Users still compare Bluetooth to IEEE 802.11b wireless fidelity (WIFI). Bluetooth consumes less power than IEEE 802.11b by factors of 10 to 100—depending on the implementation. For small instruments, in particular battery operation, this factor is critical. Second, Bluetooth is smaller to implement. Finally, Bluetooth is easier to connect to a microcontroller for instrument applications. Bluetooth has a serial connection for interface; WIFI is a complex parallel bus connection.
802.11b fulfills the majority of small office, home office wireless needs for network access; however, it is vulnerable:
- 802.11b authentication records only one of the authentication procedures, and is therefore at risk for impersonation. This is due to the fact that a cleartext ciphertext pair is the transmitter. Bluetooth communications do not share this vulnerability.
- The Ron's code 4 encryption method used in 802.11b is vulnerable to several well-known direct attacks. Direct attacks on Bluetooth encryption are computationally complex.
The events that led to Best Buy disabling their IEEE 802.11b point-of-sale terminals (people in the parking lot could use laptops to eavesdrop on transmitted credit-card information) are due to the direct sequence portion of the operation. IEEE 802.11b frequency hops until it needs to send data, then it sends a long transmission on a single frequency. This transmission is easier to intercept and is more vulnerable to interference. Bluetooth, with its packet forming and hopping, is harder to intercept and requires only the retransmission of the interrupted packet, not the entire message.
IEEE 802.11b and Bluetooth both allow networking components to communicate with each other without wires, and they both operate in the 2.4-gigahertz spread spectrum band.
Bluetooth's method of negotiating a connection requires master and slave units to acknowledge one another to form a link. IEEE 802.11b's method is not as formal, and link formation is easier, allowing pirates to gain entry.
The weakest link in Bluetooth architecture is the initial pairing, especially if a weak personal identification number (PIN) is used. For this reason, the Bluetooth special interest group recommends pairing in a private place and using complex PINs—not simple devices that use unit keys to transmit highly secure data. IT
Behind the byline
Bill Drake is manager of wireless technology at Wilcoxon in Gaithersburg, Md.
Ellen Fussell compiled this report, from Bill Drake and NeoNet Inc.
More on IEEE 802.11b
As an unlicensed use of the 2.4-gigahertz band, the IEEE 802.11b specification allows users to transmit approximately 11 megabits per second of raw wireless data at indoor distances from several dozen to several hundred feet and at outdoor distances of up to tens of miles. The distance depends on impediments, materials, and line of sight.
802.11b is an extension of wired Ethernet, bringing the same principles to wireless communication. It is primarily used for transmission control protocol/Internet protocol, but can also handle AppleTalk or PC file sharing standards. The standard is backwards compatible to earlier specifications, known as 802.11, allowing speeds of 1, 2, 5.5, and 11 megabits per second on the same transmitters. Multiple 802.11b access points can operate in the same overlapping area over different channels, which are subdivisions of the 2.4-gigahertz band available in each country. There are 14 channels, which are staggered at a few megahertz intervals, from 2.4000 to 2.4835 gigahertz. Different channels are legal in different countries, and only channels 1, 6, and 11 have no overlap among them.
Wireless facts vs. fiction
One of the most common myths surrounding wireless networks is that they will eventually replace all wired connections. However, there are several key reasons why this line of thinking is more fiction than reality.
FACT: The main reason that wireless will not replace wired is the cost difference. Wired is still cheaper than wireless, especially because wireless users have to purchase additional modems and interface equipment. Also, chips for wireless protocols cost about seven times more than chips included in hardwired products. And while the prices of wireless chips continue to fall, the wireless versus wired gap will remain significant—depending on market demand and the related volume. Because of these cost differences, wireless will be reserved to those applications that absolutely need wireless.
FACT: The capacity of a wireless network is smaller than the capacity of its wired predecessor. When network signals are sent on a wire, there is virtually no limit to the number of networks that can be installed in any plant. However, if there are too many wireless networks and devices in the same area, they will interfere with each other.
FACT: Wireless is lacking one key ingredient for the plant floor—power. No matter what type of equipment is on the plant floor, it still has to be supplied with power. Simply put, completely eliminating wires is not an option.
Source: Rockwell Automation
Comparison a moot point
Let's stop the debilitating debate over whether 802.11b or Bluetooth will win, and recognize that the two technologies are aimed at different situations. Without both technologies, the mobile device market will take far longer to develop while we wait for one of the standards to replicate the other's features. The only thing that is common is this: via a radio frequency, they both enable two or more devices to connect to each other without using a cable. That's it. The big difference is this: You use 802.11b when you want constant access to the Internet (device to server). You use Bluetooth when you have two or more small, mobile devices requiring direct connectivity for a short amount of time (device to device).
The basic differences between the two wireless communications standards are power consumption and, as a direct result, communications range. The current debate over which one will win is rather like a tempest in a teapot. We need, and have room for, both standards in the broad mobile market.
—Rebecca Taylor, Impart Technology