SI unit: Flow and density

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VTT
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This article is part of a series detailing the SI units and our calibration services. This article centers around flow and density.

Gas flows and water flows

  • Mass flow is expressed in kilograms per second (kg/s)
  • Volume flow is expressed in litres per second (l/s)

Density of liquids

  • Mass density is expressed in kilograms per cubic metre (kg/m3)

Calibration of gas flow meters, aerometers and density meters

If the relative accuracy level of a gas flowmeter is better than 1 %, the dynamic weighing system (DWS) equipment will be used in the calibration. Typical examples of such flowmeters are high-quality laminar flow elements and some piston-cylinder volume flowmeters.

Most of our customers’ flowmeters are calibrated at VTT MIKES using the calibration equipment for laminar flow elements (LFE) . It is much more convenient to use than the DWS equipment and it does not have such a strict tolerances for environmental conditions.  performing of calibrations are thus more flexible and faster. The equipment has proven to be well suited for calibration of gas flowmeters having relative accuracy above 1 %. Such meters include thermal mass flowmeters and controllers.

Furthermore, MIKES performs liquid density measurements. We calibrate for instance areometers and density meters based on vibrations and determine densities of customers own liquid samples in the density range 600 kg/m3 ... 2000 kg/m3.

Water flow meter calibrations

VTT MIKES Kajaani has three different calibration rigs for liquid flow calibrations. One of the rigs is the national measurement standard of flow. In this rig, the measuring principle is gravimetric and the measurements carried out are traceable to the national standards of mass, temperature and time.

In the closed loop type calibration rigs, the referencemeters are usually magnetic or coriolis mass flow meters. In these rigs, the source of traceaility up to DN200 is based on the national flow standard. For pipe sizes DN200 > , the source of traceability is a foreign NMI, typically PTB from Germany.

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