Jim Montague is the executive editor for Control. Email him at [email protected].
Everybody, including me, talks about how great wireless is, and how it can reduce the need for cabling and connectors and the time, labor and expense of installing and maintaining them. We also trumpet the fact that wireless lets users gather sensor data and other signals from places where they couldn’t go before, and fuels all kinds of new capabilities and performance.
However, we tend to forget some important details in all our breathless hype. Chiefly, for users who have been working with reliable hardwired devices for a long time, switching to wireless or making any other equipment change is a pain in the neck. And for users with many types of sensors, machines and production lines in various locations and distances, very different wireless methods, from Wi-Fi to radios to cellular, might be needed. This could compound the required learning and adoption curves.
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Fortunately, some developers merge these different wireless functions into combined components to make them simpler to deploy, to accept different types of wireless signals and to relay data out to more types of interfaces. Aside from facility size, adding wireless to many industrial settings is getting to be just about as easy as adding wireless to your house.
Bill Conley, systems engineering manager at B&B Electronics, reports on a water well-monitoring demonstration project he and his colleagues assembled in Arizona's Sonora desert, which includes a 600-ft-deep well with a differential pressure sensor and ground-pump current sensor, a 10,000-gallon holding tank with a level sensor, pressure pump with current sensor, 1,000-gallon pressure tank with pressure-holding sensor and an IP security camera, which all had to be remotely monitored from a residence about 600 ft away. The well's mechanical and network components must also cope with the desert's extreme temperatures, dust storms, sun damage, wind, rain, snow, lightning and accompanying power surges and electromagnetic interference.
"There are a lot of way systems like this can break," Conley says. "This application's two main weak spots are the pressure pump and the in-ground pump, which would cost $10,000 to lift out of the ground, so their current needs to be monitored. We modeled the performance of the pressure and in-ground pumps based on their SCADA performance data and found their mechanical switch was running them in a very narrow section of the holding tank and causing a lot of starts and stops. More sophisticated controls could manage the pump cycle more efficiently and extend the life of the pump."
In the past, monitoring all these devices via wireless would likely require each one to report back separately to one control room, and that centralized location would have to coordinate all those signals. One of the main ways wireless is becoming simpler is that its components gather these different signals in the field and then relay them back to one switch that can accept them all.
Conley's demonstration uses one of B&B's 900-MHz, 3G cellular routers, which can communicate with any well or other device equipped with its I/O radios within 40 miles, and make their data available via the Internet anywhere it’s needed. These radios combine analog and digital I/O and native Modbus remote terminal unit (RTU) communications, and transmit via 900 MHZ and 2.4 GHz.
"Previously, users had the option to send longer-distance signals like these over miles of fiber-optic cable or hundreds of Ethernet cables with repeaters, or use radio frequency (RF), Wi-Fi or hardwiring with extenders for local networks, and ensure power redundancy with an onsite generator with a fail-safe switch or perhaps a solar panel," Conley adds. "The solution is to have data from all the sensors go from their copper wiring to RF-enabled DAQ devices and I/O radios, and then go to a radio modem and one cellular modem to a central location."
"Consequently, instead of using several types of networks, we now combine all our Modbus telemetry in one package and convert Modbus RTU to Modbus TCP/IP in the cellular router, which allows us to add other Ethernet-based signals and add IP video inputs too. This method also lets us use 128- or 256-bit encryption and virtual private network (VPN) tunneling for security. Basically, a 3G router's ability to convert Modbus RTU to TCP/IP gives users the ability to IP-enable all their sensors from anywhere."
So while switching to wireless might not be as easy as making no changes, it's certainly getting easier to deploy it and enjoy its benefits, and getting harder to rationalize not using it.
