By Dan Hebert, Senior Technical Editor
Frequent instrument calibration using single-function, non-documenting calibrators has been the process industry norm for decades, but three technologies are changing the status quo—fieldbus networks, smart instruments and multifunction documenting calibrators. Fieldbus and smart instruments can pinpoint whether an instrument needs calibration via a reference check, essentially a truncated version of a full field calibration. The reference check can point out the need for further investigation, which can often be performed remotely by fieldbus/smart instrument diagnostics.
For most instruments, the reference check alone will show that field calibration isn't needed. Even if the reference check reveals a problem, diagnostics might show that the problem isn't significant enough to warrant full field calibration, let alone instrument replacement.
Fieldbus and smart instruments reduce the need for field calibration, and this is perhaps a leading reason why many plants have been slow to adapt multifunction documenting calibrators with accompanying calibration management software.
If a plant has 1000 dumb instruments needing to be calibrated annually, it may make sense to invest in a sophisticated calibration system. However, if fieldbus and smart instruments reduce the need for field calibration to 50 instruments a year, then a simpler calibration regime may suffice.
Our 2008 and 2010 Market Intelligence Report surveys showed that about 75% of respondents still used pen and paper to record calibration results in 2010, basically unchanged from 2008. The use of documenting calibrators also remained steady at about 25%, although the use of calibration management software increased somewhat from 43% to 49%.
A process plant may have hundreds or even thousands of instruments that need annual field calibration. This can be the case if the plant isn't using fieldbus/smart instruments; if the plant is very large; or if the plant has particular regulatory or other requirements that necessitate regular calibration.
In these cases, a high-level calibration system makes sense. "While an investment in documenting-type calibration equipment and PC-based resource management software adds additional cost, the predictive and preventative instrument performance knowledge gained are worth it," says David Matherly, the product manager of advanced product solutions at Yokogawa Corporation of America (www.us.yokogawa.com).
"When organizations move to multifunction instruments, their technicians need fewer instruments, and associated maintenance and calibration costs are lower," points out Scott Crone, product line manager for calibration products at Ametek Measurement & Calibration Technologies (www.ametek.com).
"Recordkeeping is easier as test routines can be saved, and the results can be uploaded to a PC," continues Crone. "Instrument manufacturers also typically upgrade and/or improve multifunction instruments more regularly than their single function calibrators. Manufacturers often will include or offer software to make tasks easier, reducing the time technicians need to be on station for a calibration task."
Product manager Heikki Laurila of Beamex (www.beamex.com) weighs in: "Calibration results are stored automatically, so no results have to be written down. The quality and accuracy of calibration improves as there are fewer mistakes due to human error. The calibration procedure can be automatically transferred from the computer to the handheld calibrator, ensuring it is done the same way each time. Multifunction-documenting calibrators also generate instant pass or fail messages in the field."
For process plants that need to calibrate only a few instruments a year, simple single-function calibrators might be the best solution. "Simple calibrators are often cheaper to buy, and they may be easier to use," conclude Laurila.