The tank farm was riddled with thermal relief safety valves—self-contained devices designed to ensure a blocked-in pipeline wouldn’t exceed its pressure rating due to thermal expansion. Most of them relieved to atmosphere, garnering the attention of the fugitive emissions-aware regulatory agency of the region. How could Sandra’s company assure the agency that these valves weren’t a continuous source of emissions?
Last month, we followed Sandra’s efforts to choose a network for a “pervasive networking” project. It seemed like fieldbus was easily the least expensive option for a temperature monitoring application, but she ran into resistance.
Maintenance didn’t possess a handheld licensed to connect to fieldbus segments, and was intimidated by the unfamiliar protocol that was unlike anything their technicians encountered. The ops manager was overburdened with day-to-day training and personnel concerns, let alone all the corporate initiatives that required her attendance in numerous meetings and phone conferences.
No amount of savings could persuade them to take on a perceived challenge they didn’t want or understand. The people she served were content to “do what we always did,” and her ambitions to employ a robust and substantially more capable and powerful protocol were unwelcome.
There’s a lot of reasons advocates find fieldbus—or any uncommon technology—unwelcome. In western manufacturing cultures, especially in North America, sites have been starved of personnel, and it’s been years since our numbers have been sufficient for many individuals to become subject matter experts (SMEs) in any specialty. The oft-cited expression “staffed to run, not staffed to change” applies on many levels.
With the dwindling numbers of SMEs confident enough to chart a course to deliver “certainty of outcome” for a fieldbus project, which experienced practitioners will assure you is not rocket science, solutions like WirelessHART can still find some traction. Why? Unlike bus technologies, wireless has ubiquity from laptop WiFi to cellular to the wireless router. They’re used by everyone, including Sandra’s overburdened ops manager and maintenance guys. With so many everyday appliances touting wireless, it’s a lower hurdle to overcome any FUD (fear-uncertainty-doubt) about wireless field devices in a process plant.
For Sandra’s original challenge, she was fortunate to have her device supplier suggest the more-or-less self-contained Rosemount 708 acoustic sensor, which includes an integral surface temperature sensor. This allowed it to mount to her project’s bleed valve piping without needing any process connection or thermowell. Aside from mounting and interconnecting a WirelessHART gateway and configuring a Modbus interface for the new measurements, installation was completely wireless. There were no terminations, cable or conduit to run, and since she purchased the gateway along with the sensors, both came preconfigured to interconnect on the same network.
In the months that followed, the project to install instrumentation to monitor the tank farm pipeline thermal reliefs was funded. The same instrument seemed like a great fit, but would another gateway be needed? Having obtained a new 708, Sandra found it didn’t connect immediately to their existing wireless gateway like the originals. The unique network ID and join key from the original job wasn’t entered in the new device. And there was another hurdle—the new instrument was a later revision. Its device description (DD) wasn’t loaded in Sandra’s laptop, nor was the maintenance shop’s handheld equipped to interact with it. Fortunately, her vendor’s tech support had experts on call who quickly pointed her to the website where new DDs could be downloaded, with instruction on how to add them to her laptop.
Like fieldbus, industrial wireless networks like WirelessHART are composed of digital devices on a digital network. It might be an easier technology to sell, and deployment can be easier as well. However, engineers will still need to become subject matter experts to effectively support a unique digital protocol.
