For some applications, the widely available 802.11 Wi-Fi systems are generally easy to adapt to industrial applications. The 802.11b standard has been around for years, and its maximum 11-Mbit/s data rate is almost overkill for most industrial applications. You can easily operate the Wi-Fi transceiver at one of its alternative rates of 5.5 Mbits/s, 2 Mbits/s, or 1 Mbit/s and get extra range and reliability while still providing more than an adequate data-transfer rate. The primary design challenge with using Wi-Fi is interfacing to the industrial equipment, which often involves original design.
What about the faster versions of this standard, like 802.11a and 802.11g? Both offer up to 54-Mbit/s data rates. Few if any industrial applications require this exalted rate. As for the 802.11a standard, it uses the 5-GHz band instead of the 2.4-GHz band. The range is more limited at that frequency, and range is a more important factor than speed in most industrial situations. As for the newer 802.11g, it too has overkill speed, but it does operate in the same 2.4-GHz band used by 802.11b. The really good news is that it's fully backward-compatible with 802.11b. Most Wi-Fi equipment manufacturers and the chip companies have all but totally abandoned the pure 802.11b products. So if you plan to go to Wi-Fi in an industrial setting, you'll be using 802.11g whether you need it or not.
Another option is embedded Wi-Fi. If the application is unique and you have the expertise, chips can be bought and built into the system. But a faster and easier way is to use the module approach.
One such example is DPAC Technologies' Airborne Wireless LAN module (Fig. 2). It includes the fully 802.11b-compatible radio, a baseband processor to handle the MAC functions, and an applications processor. The applications processor runs an RTOS and includes a TCP/IP stack, a command interface, and a wide range of I/O support. It handles a variety of serial I/O, including standard UART, I2C, and SPI. Up to eight parallel I/O ports are available, as are eight channels of analog. A neat feature is the built-in Web server, which allows you to remotely monitor and control any device with a browser via the Internet. With this module, you only need an antenna, a 3.3-V supply, and your I/O.
Andrew Samson, DPAC's product marketing director, indicated that the module is being widely adopted in trucking and automotive applications for diagnostics and fleet management, medical patient monitoring, and farming for automated irrigation systems. Mike Grobler, director of wireless applications for DPAC, says that 802.11b systems provide the greatest range of almost any industrial wireless technology, mainly because it transmits at the highest power permitted by ISM radios (up to 20 dBm). In ordinary situations, the range of Wi-Fi is about 100 feet at 11 Mbits/s. But longer range is possible at the lower rates. And if you use a gain antenna such as a simple Yagi, LOS range can be several miles. Also, the diversity switched antennas help mitigate multipath problems.
The industrial wireless technology with the greatest potential must be ZigBee. This short-range wireless technology was a premeditated design specifically for industrial applications. Over 80 companies have come together in the ZigBee Alliance to promote and support this technology. ZigBee is also known by its IEEE standard designation 802.15.4. The standard defines the PHY and MAC layers, while the ZigBee Alliance sets the standards for the networking, security, and applications layers.
ZigBee comes in three versions. The 868-MHz European version has a data rate of 20 kbits/s. The 915-MHz version with 10 channels has a 40-kbit/s rate. The real speed demon, the 2.4-GHz version, has 16 channels and a 250-kbit/s data rate. All use direct-sequence spread spectrum (DSSS).
Also, ZigBee is a personal-area-network (PAN) technology that can automatically establish links with nearby nodes. It can be configured in a star, tree, or mesh topology, which makes the technology ideal for mini-mesh networks.
Key benefits are ultra-low power consumption and simplicity, which ultimately translates into low cost. Industrial designers can now economically build wireless into the most mundane products, such as light fixtures and wall switches. The low power allows battery operation for up to several years in some cases.
John Adams, director of radio technology and strategy for Freescale Semiconductor (formerly Motorola), indicates that while no commercial products are on the market today, they're soon to come. He also says that the ZigBee Alliance is expected to finalize its standard in the fourth quarter of this year. The alliance will establish a testing and certification program similar to Wi-Fi to ensure standards compliance and full interoperability. Among the first commercial products expected late this year or early in 2005 are residential and commercial lighting controls for energy savings, security and fire alarms, and industrial sensors.
A typical ZigBee product is Freescale Semiconductor's MC13191/92 transceivers. These chips employ the 16-channel, 2.4-GHz band with a data rate of 250 kbits/s. They're designed for use with an 8-bit embedded controller like Freescale's MC9SO8GT family (Fig. 3). Also available is the low-cost MC13191/92 Developer's Starter Kit, which contains two sensor-application reference designs and the CodeWarrior Development Studio of software. ZigBee chips and support products additionally hail from Atmel, Betronic Design BV, Chipcon, CompXs, Microchip Technology, Rincon Research, and ZMD.
An interesting option to ZigBee is Cypress Semiconductor's WirelessUSB chips. Like ZigBee, they operate in the 2.4-GHz band using DSSS but with a data rate of 62.5 kbits/s. For simple point-to-point and multipoint-to-point applications, WirelessUSB is less expensive and simpler still than ZigBee. It doesn't have the automatic networking capability, but it's not a requirement in most applications. Carl Brasek, Cypress' product manager for USB, says that the long-range (LR) version of the CYWYSB86935 can give a range up to 50 meters, and its ultra-low power consumption makes battery power practical.
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