fluid measuring devices
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Measuring
Instrumentsuse in Fluid
Mechanics
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Manometer
Is an instrument that uses a column of liquid to
measure pressure, although the term is currently often used
to mean any pressure measuring instrument.
Types of Manometer1. Simple Manometer - is a tube, open at the top, which is
attached to the top of a vessel containing liquid at a
pressure higher than atmospheric! to be measured
". Micro manometer - # micro-manometer is a device that$s used to
measure very small di%erences in pressure in a gas or liquid
&. 'i%erential manometer -#n instrument in which the di%erence in pressure between two sources isdetermine from the vertical distance between thesurfaces of a liquid in tw
o legs of an erect or inverted (-shaped tube when each of the legs is conn
ected to one of thesources.
). Inverted di%erential manometer -It is used for measuring the
di%erence of low pressure, where accuracy is the prime consideration
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*ther Measuring 'evices
McLeod Gauge A McLeod gauge isolates a sample of gas
and compresses it in a modied mercury manometer until the
pressure is a few millimeters of mercury. The technique is slow
and unsuited to continual monitoring, but is capable of goodaccuracy. nli!e other manometer gauges, the McLeod gauge
reading is dependent on the composition of the gas since the
interpretation relies on the sample compressing as an ideal
gas. "ue to the compression process, the McLeod gauge
completely ignores partial pressures from non-ideal #apors
that condense, such as pump oils, mercury, and e#en water if
compressed enough.
#neroid
#re based on a metallic pressure-sensing element that +ees
elastically under the e%ect of a pressure di%erence across the element.
#neroid means without +uid, and the term originally distinguished these
gauges from the hydrostatic gauges described above. owever, aneroid gauges
can be used to measure the pressure of a liquid as well as a gas, and they are
not the only type of gauge that can operate without +uid. For this reason, they
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are often called mechanical gauges in modern language. #neroid gauges are not
dependent on the type of gas being measured, unli/e thermal and ioni0ation
gauges, and are less li/ely to contaminate the system than hydrostatic gauges.
ourdon 2auge
3he ourdon pressure gauge uses the principle
that a +attened tube tends to straighten or regain its circular form in
cross-section when pressuri0ed. #lthough this change in cross-
section may be hardly noticeable, and thus involving moderate
stresses within the elastic range of easily wor/able materials,
the strain of the material of the tube is magni4ed by forming the
tube into a 5 shape or even a heli, such that the entire tube tends
to straighten out or uncoil, elastically, as it is pressuri0ed.
*ri4ce 6late7
#n orice plate is a device used for measuring
the volumetric +ow rate. It uses the same principle as a
8enturi no00le, namely ernoulli9s principle which states
that there is a relationship between the pressure of the+uid and the velocity of the +uid. :hen the velocity
increases, the pressure decreases and vice versa.
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*ri4ce 6late7
#n orice plate is a device used for measuring the
volumetric +ow rate. It uses the same principle as a 8enturi
no00le, namely ernoulli9s principle which states that thereis a relationship between the pressure of the +uid and the
velocity of the +uid. :hen the velocity increases, the
pressure decreases and vice versa.
;otameter <
is a device that measures the +ow rate of +uid
in a closed tube.
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