Food Engineering

Wireless in the air

October 6, 2007


Wireless makes it easy to locate sensors in remote places and allows engineers mobility as well. Source: Emerson Process.

Wireless connectivity for industrial sensors and actuators had everyone attending “sell-out” conference sessions at the Emerson Global Users Exchange held at the Gaylord Texan Resort and Convention Center last month. Representatives from a brewery explained how they’re testing wireless transmitters in monitoring cellar temperature. A potable water authority’s engineer explained why he uses wireless sensors for monitoring pressure in water lines. Other uses for wireless include remote level metering of tanks and silos, machinery monitoring-any application where it can be costly,  impractical and expensive to run wires. Wireless communications also allow maintenance technicians and engineers to roam the plant while staying in touch with the control system.

With all the benefits of wireless, there is a wrinkle. Just like the ongoing lack of a single standard in the high-definition video disc world, there is a lack of wireless standards for plant instrumentation and controls. Many instrumentation vendors have adopted proprietary protocols, making it difficult for users to mix and match equipment from various vendors.

One solution, however, has been offered, and another is not far away. The HART Communication Foundation released its HART 7 specification, which includes the WirelessHART open communication standard specifically designed for process measurement and control (www.hartcomm.org). Many processors are already familiar with the HART protocols for wired sensors (there are 24 million devices installed), and the wireless version includes the HART protocols, IEEE 802.15.4 radio and frequency hopping, spread spectrum and mesh networking technologies. Emerson Process, Invensys and several other automation companies already support WirelessHART.

The ISA 100 standards committee (www.isa.org), Wireless Systems for Automation, has also been working on the standards issue, and is hosting a demonstration booth at its October ISA show in Houston. Unlike the single HART specification, the ISA 100 draft standard is being created as a family of standards, designed to support many applications and protocols through a single, integrated wireless network. The committee’s work will also ensure coexistence with other radio systems operating in the 2.4 GHz ISM (industrial, scientific and medical) band. The ISA 100.11a spec leverages existing technology and standards where possible to allow compliant devices to be produced quickly. Most major instrumentation vendors (process and discrete) are supporting ISA 100.