Manometer

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A manometer is a pressure measuring instrument, often also called pressure gauge.

1 Description
2 European (CEN) Standard
3 See also
4 Patents
5 External links

Description

The oldest type is the liquid-column manometer. A very simple version is a U-shaped tube half-full of liquid where the measured pressure is applied to one side of the tube whilst the reference pressure (which might be of the atmosphere) is applied to the other. The difference in liquid level represents the applied pressure. It is quite easy to make a manometer. For low pressure differences, water is a commonly-used liquid (and "inches of water" is a commonly-used pressure unit). For larger pressure differences, the greater density of mercury makes it more useful.

A single-limb liquid-column manometer has a larger reservoir instead of one side of the U-tube and has a scale beside the narrower column. The column may be inclined to further amplify the liquid movement. Liquid-column manometers can be used to measure small differences between great pressures. Image:Manometer 104026.jpg A second type uses the deflection of a flexible membrane that seals a fixed pressure reference volume to determine the pressure. The amount of deflection is repeatable for known pressures so the pressure can be determined using a lookup table.

A third variant (Bourdon gauge) uses a coiled tube which as it expands due to pressure increase causes a rotation of an arm connected to the tube.

One use of manometers is to measure vacuum pressures, especially in the range from 0.001 atmospheres to 1 atm. They are helpful because the deflection of the manometer is not dependent upon the type of gas being measured, unlike other types of vacuum gauges in this pressure range. The deflection of the piston is often one half of a capacitor, so that when the piston moves, the capacitance of the device changes. This is a common way (with proper calibrations) to get a very precise, electronic reading from a manometer, and this configuration is called a capacitive manometer vacuum gauge.

For very low pressures (high vacuums, AKA "hard" vacuums), entirely electronic means (ion gauges) are used to measure the quality of the vacuum.

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European (CEN) Standard

EN 472 : Pessure gauge - Vocabulary.
EN 837-1 : Pressure gauges. Bourdon tube pressure gauges. Dimensions, metrology, requirements and testing.
EN 837-2 : Pressure gauges. Selection and installation recommendations for pressure gauges.
EN 837-3 : Pressure gauges. Diaphragm and capsule pressure gauges. Dimensions, metrology, requirements and testing..

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