OPEN SOFTWARE OPENS YOUR CHOICES
From a systems point of view, data from wired and wireless sensors alike is transmitted to a measurement system. The measurement system is typically a programmable logic controller (PLC), an industrial PC, or some kind of programmable automation controller (PAC). Often, this sensor data is also needed at the enterprise layer.
According to Robert Jackson, product manager of National Instruments, you can use software that supports multiple standards. This allows users to select the best wireless protocols for the application. NI’s LabVIEW software can be used to connect ZigBee or other 802.15.4 battery-powered nodes through Lab- VIEW instrument drivers that are available for Banner, Crossbow, Accutech, and Accsense gateways. Or, they can select Modbus to connect to other wireless gateways.
By using LabVIEW on a PC or a real-time PAC, you can then integrate wireless data from different vendors, combine it with wired measurement data, and share it at the enterprise layer (Fig. 2). Wi-Fi 802.11 is often selected to share data between distributed measurement systems and PCs and laptops due to its broad availability.
New Wi-Fi devices like NI’s WAP3701 industrial-grade wireless access point provide what’s needed to deploy Wi-Fi in industrial environments. With this approach, you can integrate wireless technologies into existing systems and select multiple protocols to best fit the application.
THE LATEST PRODUCTS
B&B Electronics, a longtime supplier of wire, cable, and communications I/O for industrial applications, now carries a wide range of wireless options. For example, its proprietary Zlink radio modems and I/O module units use the popular Modbus protocol (Fig. 3).
Models are available to operate in the 900-MHz or 2.4-GHz bands with different power levels. Modulation is frequency shift keying (FSK), and data rates of 9600 bits/s to 115 kbits/s are available. Different power output options let you select a model for the range you need. The I/O serial communications can be RS-232, RS-422, or RS-485.
According to Dennis Fairfield, B&B’s wireless product manager, the Zlink products’ key feature is a wide range of matching I/O modules to accommodate both digital and analog I/O. Analog I/O may be 4 to 20 mA, 0 to 20 mA, or 0 to 10 V. Digital inputs in the 0- to 48-V range can be used, and digital outputs in the 10- to 48-V range are possible. Options for temperature sensors, including resistance temperature detectors (RTDs), are available.
Banner Engineering’s SureCross Wireless network is a rugged wireless I/O solution that can fit a wide range of applications. The SureCross Network uses a node transceiver to collect data that’s then transmitted to a gateway system controller. This bidirectional system can be used to build a variety of monitoring and control systems. The radios are available in either 900-MHz or 2.4-GHz models. They all use a proprietary protocol.
The technology is frequency-hopping spread spectrum with FSK modulation. A time-division multiple-access (TDMA) scheme provides two-way time slots for data and control signals. With standard antennas, the 900-MHz version can achieve a range to three miles, while the 2.4-GHz version can reach a maximum of two miles.
The SureCross system is compatible with an extensive range of sensors, including RTD, themistor, thermocouple, photoelectric, ultrasonic, capacitive, inductive, pressure, contact closure, and flow. Models are available with a mix of both analog and digital I/O lines. SureCross also supports other serial communications formats, such as Modbus RTU RS-485, Modbus RTURS- 232, Modbus TCP/IP, and Ethernet/ IP. Banner has a new wireless developer’s evaluation kit for the SureCross system, designated DX70, as well.
Digi International’s recent acquisition of Maxstream gives it a real ZigBee presence. Its XBee Znet and XBee-PRO modules are designed for OEM applications (Fig. 4). They drop right into other products or can be used to quickly and easily set up full-blown mesh networks. The company’s XBee Wall Router plugs into an ac outlet and provides repeater functions to extend a mesh network.
Meanwhile, the Digi Connect WAN 3G wireless router supplies connectivity to remote sites and devices (Fig. 5). This Ethernet- to-cellular router supports both HSDPA and EV-DO 3G cell-phone technologies. It also provides primary wireless wide-area network (WAN) connections to remote sites containing Ethernet and serial devices, such as construction sites, power utility substations, retail point-of-sale (POS) sites, temporary facilities, and other remote places where a wired network isn’t feasible.
The Digi Connect WAN 3G features a built-in virtual private network (VPN) for secure connections, one Ethernet port, one serial port, a sensor port for connecting Digi’s Watchport sensors, and a USB port for connecting to Digi’s Watchport USB camera or for an external GPS device. According to Lynn Linse, principal engineer with Digi, the company makes a full line of other wireless products, both standard wireless and proprietary, for just about any application, plus all of the support software.
Freewave Technologies’ licensed FGRIO-S30 Modbus Industrial radio uses the 900-MHz band. Also, its 1-W transmitter can extend range to 40 miles or more. It’s ideal for long-range remote control and monitoring of tanks, lifting stations, pumps, flow meters, fluid levels, water sources, temperature and pressure, and the water/wastewater, oil, and gas industries.
Like other wireless industrial products, its main function is to reduce costs for wiring while providing solid, reliable connections to the system. The FGRIO-S30 can deliver data from remote analog (4 to 20 mA or 1 to 5 V dc) and digital sensors or third-party equipment over a wireless link to a remote terminal unit (RTU) or PLC. It can operate in either the Modbus mode or the wire replacement mode.
In addition, it offers two analog outputs in the 0- to 22-mA range and two digital inputs up to 1000 Hz for counters. Furthermore, it can program digital outputs to self-shutoff after a programmed interval to safeguard intermittent-rated loads. All analog inputs are read as both 32-bit floating point and 16-bit integer formats to reduce the computation required at the RTU. The FGRIO-S30 is available now.
Micrel’s MICRF218 receiver, which is part of the company’s QwikRadio family, is the first programmable receiver with jam avoidance. This amplitude-shift-keying/on-off keying (ASK/ OOK) receiver operates in the 300- to 450-MHz range and targets garage door openers, tire-pressure monitoring systems, and a variety of critical industrial-control applications. It also has a selectable IF bandwidth.
Its maximum data rate is 10 kbits/s using Manchester coding. An analog received signal strength indicator (RSSI) output is provided. This unique chip can detect interference on one channel and switch to another. It also can accommodate two different crystals to set the operating frequency using an external switch. The IF bandwidth and data filtering are selectable. The chip is available now for $1.71 in 10,000-unit quantities.
RF Technology’s TinyOne Lite 433-MHz low-power radio module boasts an output power of 10 mW and receiver sensitivity as great as –102 dBm, achieving a maximum range of about 500 meters depending on environment and antennas. It supports data rates of 10, 38.4, 100, and 115.2 kbits/s. The modulation is Gaussian frequency-shift keying (GFSK) in the 433.5- to 434.7-MHz ISM range. The input is RS-232 and TTL.
Finally, One RF Technology offers the S-One and M-One stacks. The M-One stack is ideal for mesh networks in home applications, sensor networks, and irrigation systems. One RF Technology also provides other radio modems for the 868- and 915-MHz and 2.4-GHz bands, including ZigBee.
Need More Information?
B&B Electronics • www.bb-elec.com
Banner Engineering • www.bannerengineering.com
Digi International • www.digi.com
Freewave Technologies • www.freewave.com
Micrel Inc. • www.micrel.com
National Instruments • www.ni.com
One RF Technology • www.one-rf.com
Wireless Industrial Networking Alliance • www.wina.org
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