-- A new chapter in the saga of calibration versus verification of critical measurement equipment has been opened by the marketing of new liquid flow meters that imply there is no longer a need to calibrate in-situ pipeline flow meters.
The traditional flow meter “wet calibration” process can be tedious, time consuming and result in weeks of downtime, especially if sterile environments become contaminated. Some new flow meter designs in today’s market offer self-verification circuits designed to provide an accuracy check on the flow meter without removing the meter from the process. Marketing of the self-verification method purports the risks associated with traditional in-situ flow meter calibration can be eliminated using these new meters, but others in the industry are warning of the business risks to such an approach.
Brandon Goodman, founder and president of Morristown, TN based Precision Calibration Systems warns “The only way to properly calibrate a meter or a system is to compare the measurements it provides against NIST traceable standards and make adjustments to the nominal until the differences observed are within tolerance.”
The danger associated with on board verification is that the end user often uses the verification data in place of actual NIST traceable calibration data when assessing drift. If a meter or instrument isn’t calibrated against a NIST traceable standard, the accuracy of drift over time cannot be accurately accessed. This practice can pose a serious risk to manufacturers who could be unknowingly producing non-conforming product which results in the loss of competency of quality control systems, consumer confidence and ultimately the loss of company revenues.
Calibration requirements are placed on all instruments that measure critical parameters that directly affect the quality of the product being produced by FDA, IATF 16949 and ISO 9001 compliant quality systems. The industrial sectors with most to lose from eliminating calibration of in-situ flow meters include pharmaceutical, semiconductor, oil and gas, fresh water and sewage industries.
As previously mentioned, traditional wet calibration methods in which the meters are removed from their respective processes can certainly be invasive and cause excessive downtime. Goodman suggests a better approach is to use external ‘clamp-on’ master flow meters that maintain measurement integrity and NIST traceability. Advancing technology has made it possible to get accurate flow readings with uncertainties as low as 0.6% even in “ultra-pure” water applications. These highly advanced systems use ultrasonic waves to measure flow without ripping the pipeline apart. The master is calibrated to NIST standards and can therefore transfer that integrity to the in-situ meter.
Goodman notes “It may appear attractive to replace calibration with instrument verification, but where does the argument end and what could be the cost to customers and consumers?” ‘Will we soon see manufacturers of other instruments declare their systems capable of performing self-verification, thus completely eliminating calibration and accountability?’“Calibration is vital to ensure quality is maintained and product integrity is preserved; it enables businesses to have confidence in the results that they monitor, record and subsequently control.”
Precision Calibration Systems offers their Signature Service on many meters and instruments. Expedited service is the norm at PCS and is not charged at a premium rate. The company provides the fastest, documented calibration service in the USA.
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