From Flow Measurement
Meter manufacturers and users utilize laboratories with primary flow standards
to calibrate their working flowmeter standards. Such laboratory standards are
designed to have the lowest practical measurement uncertainty so that this high
accuracy can be passed on to the flowmeter being calibrated and subsequently to
the flowmeter application. Laboratory standards are used to assess flowmeter performance
under ideal conditions (generally field performance is not as good).
Presently, the uncertainty of laboratory standards is reported to be typically less
than 0.2% with a 95% level of confidence. All of the uncertainties herein will be
expressed as 95% level of confidence values unless otherwise stated. Laboratory
flow standards exist for liquid flows from approximately 0.1 g/min to 10,000 kg/
min and for gas flows from approximately 1x10-6 g/min to 100 kg/min. The low
uncertainty requirement generally means that these devices are used in tightly
controlled laboratory environments and are not portable. Laboratory flow standards
can be grouped into certain general categories, and examining their principles
and methods of operation is useful for those seeking to establish a flow
calibration laboratory or understand the laboratory calibration process. Laboratory
standards are typically custom-built devices, unique in design, but some commercially-
built laboratory standards...
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