Calibration / Fieldbus / Wireless

Easier Commissioning with Wireless

With a Capable System, the End User Is Mouse-Clicks Away From Knowing 99% of What He Needs to Know About the Device Without Ever Lifting a Wire

I always admired and valued the techs that would show up for the job with a tool apron chock-full of digital multimeters, analog calibrators, trim pot screwdrivers, test leads, handheld communicators, you name it. My friend Al was one of these guys: ready for any contingency and no tedious trips back to the shop to retrieve the necessary tool. In 1980 or 1990, even in 2000, Al's tools and methods were how you went from broken to functional. But today, users and their service providers who set out to impose the paradigms of the 4-20 mA era can be inefficient at best. In the worst case, the old ways can create some angst and frustration.

Al's been retired for a few years now, and to some degree we're retiring some of his tools. Loop check and commissioning teams still need them in their toolbox, but the degree to which the last generation of tools are necessary is declining. Practically every device has a microprocessor in it, and if the end user is exploiting standard protocols for digital integration—Foundation fieldbus (FF), Profibus PA or HART—the vital information is knowable within moments of landing the wires. With a capable system, the end user or start-up technician is mouse clicks away from knowing 99% of what they need to know about the newly terminated device without ever lifting a wire.

It's true that with wired HART you still have some dealings with analog 4-20 mA, but it's common for HART devices to support methods for simulating loop current, as well as an "analog trim" function. As with the more modern protocols, it's common for the user to invoke these functions with mouse clicks. WirelessHART and ISA 100.11a devices are on par with the fieldbuses because they're virtually all digital from the time they're powered up. The suppliers that support these protocols are the leaders in our industry, and they've made great strides in making complex commissioning of digitally integrated devices, whether fieldbus, HART or wireless, as painless and streamlined as possible. You can get most of the job done and find the vast majority of errors whilst sipping your tea in the comfortable, air-conditioned control house.

Once your device is powered up and talking to the host without errors, showing the proper tag number and service, what else do you need to check? Well I'm afraid some trips to the plant are still needed. Maybe you want to pump up some DP cells to do a range validation, but I wouldn't endorse an in-place "calibration" of pressure devices unless such a range check reveals an unacceptable error. But you can't apply pressure to vortex shedding meters, ultrasonic meters, radar or nuclear. What our plants have done for FF is simply to verify "the right tag in the right place" by momentarily disconnecting the device locally, and verifying the corresponding tag in the DCS. We do this again in the field junction box to ensure the pairs are properly tagged. The person in the house can check everything else—alarm settings, linearization, full scale engineering units, interlocks—without ever leaving his seat.

This method does require a systems-savvy individual at the engineering workstation. There's a new way to relieve this person of commissioning duties and make loop check a one-person job. You can use 802.11a/b/g/n wireless Ethernet to port a remote client session from your engineering workstation to the field. The "system" view is portable and can, in theory, be viewed from each device as it's tested. For the commissioning stage, concerns about stringent network security and area classification might be less than the operating phase, but there's a good chance your client will want the wireless network to persist beyond start-up. One's "mesh" access points can be relocated as needed to facilitate the areas that are ready to commission.

Provided we can address concerns about security, the potential for "mobile worker" applications is considerable. Check with your systems supplier about the ways they can help.