Wireless Smart Devices: Unhand Me, Handheld!
Handhelds: What's Not to Love?
Where's the HART communicator? A little crisis ensued when a multiplexer channel became finicky about detecting a new HART transmitter; we needed to configure the proper range, signal conditioning and tag number. We've grown accustomed to interacting with "smart" devices—both fieldbus and HART 4-20 mA—from the comfort of the engineering or asset management interface. Our head technician stopped sending in our old 275 HART communicators for updates years ago. As with many of the tools of yore, not only do we forget how to operate them, but we also forget where we put them. "I hope the batteries aren't dead," I thought.
Eventually, the 275 turned up, and we even remembered how to store the configuration from one of its triple-redundant siblings and blast it into the new device. Whew! I guess we better take care of those old 275s.
Then a valve came back from vendor's shop with a brand-new, fieldbus-capable DVC6000 positioner on it. Now, every one of the hundreds of devices we've connected to our DCS has dutifully appeared in the engineering interface before, but this positioner didn't. Could there have been a mix-up? Was it actually a HART device? No, physical inspection confirmed it was Foundation fieldbus (FF).
The vendor suggested we might want to check the address. Since our DCS couldn't "see" the device, we didn't know how to do that. We needed—a handheld. Since our 275s don't speak FF, we had to borrow a 375 from a neighbor. Sure enough, the address had been set at the vendor's shop to "123," which happens to be an address where the DCS interface card (the H1 link master) doesn't knock. The 375 allowed us to set a compatible address, and commissioning resumed without issue.
More recently, we wanted to add a new WirelessHART transmitter to our existing WiHART network. We'd set up the original dozens of devices in the comfort of the shop, powering up each device individually and configuring it when it appeared in the browser interface. But now the new transmitter didn't want to join its siblings on the original network. The new device needed to be configured with a compatible network ID and a join key before it could be seen through our gateway. Drat! I believe I need a handheld! This time we had to find a neighbor with a 475, the latest incarnation of Emerson's smart communicators. Lucky I have nice neighbors.
The other routine function for which handhelds prove hard to beat is in-place calibration. It's a challenge to drag a dead-weight tester around in the field, so if you don't want to bring every device into the shop for calibration, you'll likely need a handheld. Calibrators from Fluke, Meriam and GE (Druck) have innate HART capability, and Beamex also includes connectivity for fieldbus.
There's also a cadre of communicators that enable "BYOD." If you have Windows notebooks or tablets that can be safely used in your operating areas, adapters for HART and FF are available, as well as custom software and more standardized FDT-DTM applications. I have a feeling iOS and Android apps for interacting with smart devices are in the not-distant future.
Handhelds: what's not to love? For one thing, they're an agent of database entropy, increasing fragmentation, randomness and undetected/undocumented configuration changes and errors. Without a centrally maintained database, a team of technicians can cause your management-of-change some stress. Conceivably, any organization can develop the procedures and discipline to track instrument changes, but you'd like a method that relies less on the multiple keystrokes of a random instrument specialist on a HART communicator. If only handhelds connected directly to a single host database.
Even with their disadvantages, I can't seem to shake loose of handhelds. It looks like they'll have a "hand" in my budget for many years to come.
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