Defined as all-in-one battery-powered field devices connected wirelessly to base radio gateways, wireless sensor networks have gone from taboo to default in a rapidly increasing number of applications. "It's the fastest growing product line in our history," said Steve Goodman, senior product manager, Telemetry and Remote SCADA Solutions Group, Schneider Electric, to attendees of his session at the company's 2015 Global Automation Conference, today in Dallas. The CAGR is 40% over the past five years.
The process industries buy most of it to relieve pain points including:
- Processes at a distance where information is stranded due to the cost of wiring;
- Rapid network deployment, for example, for urgent regulatory compliance such as leak detection;
- Easy network deployment, without engineering.
"Wireless is easy to install, configure and maintain," said Goodman. "Today, it offers long battery life, long distances, a wide range of sensors, and immunity to noise as well as harsh and hazardous environments."
The main area of implementation has shifted from water/wastewater to oil & gas, "but it can be used anywhere," Goodman said, "to monitor temperature, pressure, flow, level, on/off, and digital and analog I/O." It also can be used to control a valve, to monitor acoustics, and on moving equipment such as the drum of a cement kiln.
License-free bands include 900 MHz in North America, Australia and Brazil, and 2.4 GHz in the rest of the world. "900 MHz bounces off the walls and travels a kilometer or more, giving a very good signal," Goodman said. "2.4 GHz goes about half as far, which is still good."
Schneider Electric's Accutech field devices are Class I, Div. 1 intrinsically safe. "Their lithium thionyl batteries have tremendous energy density – at least three years at once every 10 seconds – and are easily replaced," Goodman said.
Their proprietary WiSTAR protocol allows one base radio to handle as many as 100 field units, and as many as 256 networks can coexist. "They're not pinged," said Goodman. "They're almost dead when they're sleeping, then wake up on schedule at a time that's previously arranged by the receiver, to deliver their measurement in milliseconds. That's why the batteries last so long."
The units are easily deployed using a built-in interface and two thumbs. "You can connect to them from the base radion using a PC, but most people just use their thumbs on the devices," Goodman said. They mount on a single fitting or with a U-bolt. Remote antennas and sensors are available for odd applications such as manholes and hot areas.
The base radio communicates to a PLC, RTU or long-distance radio via Modbus RS485/232, or to a DCS via an analog/discrete output module. Security comes from not using any IP addresses and through optional use of a built-in capability for a four-digit authentication code.