This article was printed in CONTROL's August 2009 edition.
By Jim Montague
Wireless is getting easier. No kidding. Just a few years ago, when wireless technologies began to migrate from old-time radios to digital nodes and fieldbus-like networks, much of the initial advocacy focused on it as a logical replacement for hardwiring. Consequently, discussions about how to implement it focused on the physics of wireless transmitters, antennas, coverage areas, signal strength, frequencies, bandwidth, data rates, packet sizes, switching and other interference-limiting issues that could make it as reliable and familiar as hardwiring.
Since then, some increasingly brave souls have adopted a variety of wireless methods. And many wireless devices and their underlying software are steadily improving, removing early technical barriers, and making many wireless tools far easier for even novice users to understand, set up, program, configure and deploy. Now, those early adopters are extending their leads because they have the wireless experience, foundation and conceptual know-how to fulfill the original potential of wireless and take it in directions it was probably supposed to go in the first place.
For example, engineers at StatoilHydro ASA's (www.statoilhydro) Gullfaks A, B and C platforms in the Norwegian North Sea were recently losing flow due to a loss of wellhead pressure from the 90 wells supplying the platforms (Figure 1). Early flow-loss detection helps operators flow the well through a test separator, reestablish flow by reducing pressure and bring flow back quickly to improve throughput and production.
However, StatoilHydro reports flow loss at the three platforms was very hard to detect because there were no flowmeters in the well pipes. Also, manual readings were taken only at the beginning and end of a shift, so a flow loss could easily go undetected for a long time. Unfortunately, installing flowmeters in the wells wasn't practical because it would have required a complete and prohibitively costly production shutdown. As a result, the company's engineers decided a non-intrusive solution was required, but also knew that new sensors would need a link back to the control room. However, the wellheads were very crowded and had to be kept clear for safety, so introducing added cabling, trays and junction boxes wasn't possible.
To automate its flow loss monitoring unobtrusively, secure real-time data and reduce personnel presence in hazardous areas, StatoilHydro's engineers implemented a pilot wireless project on its Gullfaks A, B and C platforms by installing Emerson Process Management's (www.emersonprocess.com) 648 wireless temperature transmitters to indirectly indicate flow on lines at each of 40 wells. Equipped with the HART Communication Foundation's (www.hartcomm.org) WirelessHART protocol and Emerson's SmartWireless capabilities, the three platforms' new wireless devices transmit readings every 30 seconds from clamp-on temperature sensors mounted on the surface of the flow pipes and send them back via a Smart Wireless gateway. Tormod Jenssen, staff engineer for plant integrity at the Gullfaks field, adds that, "Emerson's wireless transmitters enabled quick and reliable detection of lost flow and allowed immediate action to re-establish flow and increase production."
Anders Røyrøy, StatoilHydro Norway's project manager for R&D projects, adds, "Installing added wired measurement points at the wellhead would have meant lots of wiring and long cable trays. However, we were able to install the new wireless devices very quickly. Typically, it only took a few hours to install each wireless device, compared to up to two days for each hardwired device. Wireless offers an inherent reduction in cabling infrastructure, complexity and weight, resulting in lower installation costs. Because there's daily radio communication in the well area, it's essential that the wireless field network coexist without reduced performance. Smart Wireless mitigates the impact of interference, and the data reliability is 100%. Rich process information and plant diagnostics are essential for unmanned operation, and by introducing Smart Wireless transmitters to our platforms, we're making broad strides towards our goals."
More recently, StatoilHydro added more Smart Wireless devices at Gullfaks, for a total of 90 wireless transmitters covering all production flow lines on the three platforms.
To secure both the obvious and less-apparent advantages of wireless, veteran users and system integrators have several primary recommendations—even though every process application has its own unique characteristics and needs.
Steve DeHaan, P.E., engineering vice president at Technical Systems Inc. (www.tsicontrols.com) in Lynnwood, Wash., says potential wireless users should first learn the basics of radio frequency propagation for the various frequency ranges, and then understand the various radio frequency (RF) network architectures and communication methods, including point-to-point, point-to-multipoint, mesh, store-and-forward, repeaters and others. TSI is a large system integrator that's worked in the water and wastewater market for nearly 40 years. It has experience in radio telemetry systems, and most of the systems it has installed use FCC-licensed frequencies in the 170 MHz to 460 MHz range due to the site-to-site distances, terrain and tall trees common on the U.S. West Coast. TSI also has experience with 900MHz and 2.4GHz systems for higher bandwidth applications, such as wireless Ethernet.