Flow measurement

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Flow mea­sure­ment is the gener­ic term for the mea­sure­ment of a vol­ume flow per unit of time. The most com­mon unit of mea­sure­ment is cu­bic me­ters per sec­ond (m³/s), but oth­er units are al­so common.

In prac­tice, de­vices ac­cord­ing to DIN 1319 are used for flow mea­sure­ment. De­pend­ing on the ap­pli­ca­tion, they are of dif­fer­ent de­sign and fol­low dif­fer­ent mea­sur­ing prin­ci­ples. Among oth­ers, these de­vices are fre­quent­ly found in in­dus­tri­al applications:

• Swash plate me­ter: Us­es wa­ter flow­ing in­to a cham­ber to cause the wob­ble plate to move. The to­tal num­ber of swings in a giv­en pe­ri­od of time in­di­cates the flow rate.
• Elec­tro­mag­net­ic flow me­ter: Us­es a mag­net­ic field that cre­ates a volt­age in the medi­um through pos­i­tive and neg­a­tive charge car­ri­ers. The volt­age is used to in­fer the flow rate via the flow velocity.
• Ul­tra­son­ic flowme­ter: Us­es an acoustic sig­nal. The time it takes for the wave to trav­el through the medi­um in­di­cates the cur­rent flow rate.
• Im­peller me­ter: Us­es an im­peller that gen­er­ates a sig­nal pro­por­tion­al to the flow rate.
• Mass me­ter: Us­es an elec­tri­cal heat­ing wire and two tem­per­a­ture sen­sors. The min­i­mum heat­ing of the vol­ume flow by the heat­ing wire is sensed by the tem­per­a­ture sen­sors and the flow rate is in­ferred from the tem­per­a­ture dif­fer­ence at the two dif­fer­ent points.
• Dif­fer­en­tial pres­sure flow me­ter: Use the pres­sure drop at a de­lib­er­ate­ly con­strict­ed point to in­fer flow rate via Bernoulli’s equation.

What should be considered when selecting a flow meter?

The prop­er­ties of the medi­um be­ing mea­sured are crit­i­cal to the prop­er se­lec­tion of the de­vice. Den­si­ty, tem­per­a­ture, pres­sure, con­duc­tiv­i­ty and vis­cos­i­ty should be considered.

Where are flow measurements performed?

Flow mea­sure­ments of liq­uid and gaseous me­dia are per­formed in many ar­eas. Ex­am­ples would be:

• Wa­ter and waste water
• Chem­istry and petrochemistry
• Oil and gas
• Pow­er and steam generation
• Phar­ma­ceu­ti­cals
• Pulp and paper
• Food and beverage

Flow measurement is also a performance component in on-site visualization

hy­drother­mal process­es in process wa­ter cir­cuits of in­dus­tri­al tem­per­a­ture con­trol sys­tems. Ba­si­cal­ly, flow mea­sure­ment al­ways al­so pro­vides in­for­ma­tion about the ef­fi­cien­cy and per­for­mance of a flu­id pow­er sys­tem. With a da­ta log­ger, the flow can be mea­sured at two dif­fer­ent points and tracked over a longer pe­ri­od of time.

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