Catching the Drift

Calibration Software Beats Spreadsheets for Managing Complexity, Reducing “Field Trips” Without Risk and Even Predicting the Next Time an Instrument Will Drift Out of Spec

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“While there’s a big switch to HART and Foundation fieldbus devices underway, acceptance has not reached the tipping point yet,” says Ed Shuler, senior applications engineer with Honeywell Process Solutions. So it stands to reason that users in primarily analog plants represent the largest share of CMS usage.

The availability of calibrators can be a limiting factor because “many do not conform to the open FCINTF [field interface] standard and, therefore, can only be used with a proprietary CMS,” adds Olson.

Likewise, few calibrators on the market to date offer Foundation fieldbus compatibility to fully automate the data from smart instruments. HART-compliant devices are more abundant, albeit with varying degrees of support.
Foundation fieldbus or Profibus connections also can take advantage of calibration automation software features, but availability is still limited. As a result, says Olson, “Many times, maintenance treats the calibration of these devices as if they were working on a 4-20 mA device by manually logging the results of the calibration.”

Regs and the PDA Upload Solution

The U.K. pharmaceutical engineer mentioned above uses an “RX” edition of Honeywell’s DocuMint software, but test results are entered manually. Protocols and documentation are downloaded from the software to the calibrator, but the results are manually keyed into a standard PDA that, unlike calibrators, allows secure user ID sign-in. When data is uploaded to the PC software, its contents, including that user ID, is saved to a primary, uneditable report.

The user says the software helped produce a tremendous turnaround for his regulatory compliance effort; resulted in an always audit-ready operation; and “transformed the standards we have in terms of record keeping, audit trails and compliance overall, which was the primary reason that we put it in.”  

Maintenance Systems Integration

If a company’s requirements include CMS data integration with plant asset maintenance (PAM) or enterprise systems, then this knowledge could help whittle down some of its software choices.

Scharf and her associates at New England Controls gravitate toward Beamex calibrators and software for their interface and calibration database functions. In contrast, she recommends Emerson’s AMS plant maintenance system’s Device Manager with a Calibration Assistant “Snap-On” for plants in that vendor’s DCS environment who want an asset management tool. The latter is an integrated environment that combines calibration management with overall instrument maintenance and process control.

DCS vendors offer CMS/PAM solutions developed in-house or through partnerships to simplify the user experience and consolidate calibration alerts, such as calibration due, with all other asset monitor alerts, such as pressure over-range for each device,” explains Olson. In addition, he adds that all such systems, including his company’s Mobility Device Management System, tie to the higher-level Asset Master. Most DCS/PAM system vendors only support a single, preferred calibration software package.

Instrumentation and calibrator companies are similarly seeing an opportunity for integration, including Endress+Hauser, whose CompuCal connects with the higher-level FieldCare package—and an online portal for storing backup calibration tests and documentation, “so those calibration certificates will never be missing when an inspector comes by,” says Ben Keizers, E+H’s product marketing manager for services. And for a ubiquitous, intranet connection, CalWorks, from Norvada, goes a step further with a full, web-based CMS.
Larger CMS/PAM packages also have added interfaces to IBM’s Maximo asset maintenance system and SAP’s plant maintenance and workflow functions. 

Predicting Drift, the Calibration ‘Grail’

In process control, digital instrument information, including calibration trends, have been touted as helping plants move from scheduled, preventive maintenance to predictive maintenance. But few realize how calibration deviation trends can be used for predictive maintenance.

In a predictive, condition-based maintenance program, a work order is scheduled, based not on calendar dates or hours of operation, but on when the instrument engineer can demonstrate that the calibration will drift. The benefits here include reduced disturbance to sensitive instruments fewer scheduled field trips.

Consider the trend that results from repeated tracking of transmitter output values from a five-point calibration. CMS screens calculate and display the deviations over time, allowing the user to extrapolate when the instrument will drift next. “So in theory, you can go out two weeks before the instrument is going to drift out of spec and recalibrate to bring it back down close to 0% error,” says Honeywell’s Shuler (See “How to Predict the Next Deviation”).

Engineers proficient with condition monitoring from vibration to lubrication oil analysis know that scheduled work orders aren’t eliminated, but in an asset-intensive environment, over time benefits can be gained in compliance, performance and cost reduction.

Whether a plant is operating in full, analog or digital mode, sets its goals on stand-alone or integrated data flows, or cares to embark on predictive calibration maintenance, the first step is to take a look at the benefits CMS can bring.

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