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All You Need to Know About Pressure Measurement

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All You Need to Know About Pressure Measurement

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  1. All About Pressure Measurement Created by Precision Mass

  2. What is Pressure Measurement? • Pressure measurement is the analysis of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. • Instruments used to measure and display pressure in an integral unit are called pressure meters or pressure gauges or vacuum gauges. • A manometer is a good example, as it uses the surface area and weight of a column of liquid to both measure and indicate pressure.

  3. Absolute, gauge and differential pressures — Zero Reference • Everyday pressure measurements, such as for vehicle tire pressure, are usually made relative to ambient air pressure. • In other cases measurements are made relative to a vacuum or to some other specific reference. When distinguishing between these zero references, the following terms are used: • Absolute Pressure • Gauge Pressure • Differential Pressure

  4. Absolute Pressure • Absolute pressure is zero-referenced against a perfect vacuum, using an absolute scale, so it is equal to gauge pressure plus atmospheric pressure.

  5. Gauge Pressure • Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. • Negative signs are usually omitted. • To distinguish a negative pressure, the value may be appended with the word "vacuum" or the gauge may be labeled a "vacuum gauge". These are further divided into two subcategories: high and low vacuum. • The applicable pressure ranges of many of the techniques used to measure vacuums overlap. Hence, by combining several different types of gauge, it is possible to measure system pressure continuously from 10 mbar down to 10−11 mbar.

  6. Differential Pressure • Differential pressure is the difference in pressure between two points. • Differential pressure is more complex than Gauge or Absolute pressure as it has two variables.

  7. Instruments • Many instruments have been invented to measure pressure, with different advantages and disadvantages. • Hydrostagic • Piston • Liquid Column • McLeod • Aneroid • Bourdon • Diaphragm • Bellows • Magnetic Coupling • Spinning Rotor Gauge

  8. Piston Type Gauges • Piston-type gauges counterbalance the pressure of a fluid with a spring (for example tire-pressure gauges of comparatively low accuracy) or a solid weight, in which case it is known as a deadweight tester and may be used for calibration of other gauges.

  9. Liquid Column Gauges • Liquid-column gauges consist of a column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight (a force applied due to gravity) is in equilibrium with the pressure differential between the two ends of the tube (a force applied due to fluid pressure). • A very simple version is a U-shaped tube half-full of liquid, one side of which is connected to the region of interest while the reference pressure (which might be the atmospheric pressure or a vacuum) is applied to the other.

  10. McLeod Gauge • A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few millimeters of mercury. The technique is very slow and unsuited to continual monitoring, but is capable of good accuracy. • Unlike 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.

  11. Bourdon Gauge • The Bourdon pressure gauge uses the principle that a flattened tube tends to straighten or regain its circular form in cross-section when pressurized. • This change in cross-section may be hardly noticeable, involving moderate stresses within the elastic range of easily workable materials. • The strain of the material of the tube is magnified by forming the tube into a C shape or even a helix, such that the entire tube tends to straighten out or uncoil elastically as it is pressurized.

  12. Diaphragm • A second type of aneroid gauge uses deflection of a flexible membrane that separates regions of different pressure. The amount of deflection is repeatable for known pressures so the pressure can be determined by using calibration.

  13. Bellows • In gauges intended to sense small pressures or pressure differences, or require that an absolute pressure be measured, the gear train and needle may be driven by an enclosed and sealed bellows chamber, called an aneroid, which means "without liquid". • Early barometers used a column of liquid such as water or the liquid metal mercury suspended by a vacuum. • This bellows configuration is used in aneroid barometers (barometers with an indicating needle and dial card), altimeters, altitude recording barographs, and the altitude telemetry instruments used in weather balloon radiosondes.

  14. Magnetic Coupling • These gauges use the attraction of two magnets to translate differential pressure into motion of a dial pointer. • As differential pressure increases, a magnet attached to either a piston or rubber diaphragm moves. • A rotary magnet that is attached to a pointer then moves in unison. To create different pressure ranges, the spring rate can be increased or decreased.

  15. Spinning-Rotor Gauge • The spinning-rotor gauge works by measuring the amount a rotating ball is slowed by the viscosity of the gas being measured. The ball is made of steel and is magnetically levitated inside a steel tube closed at one end and exposed to the gas to be measured at the other. • The ball is brought up to speed (about 2500 rad/s), and the speed measured after switching off the drive, by electromagnetic transducers. • The range of the instrument is 10−5 to 102 Pa (103 Pa with less accuracy). • It is accurate and stable enough to be used as a secondary standard.

  16. For More Information on Pressure Measurement, Contact with Us: • Website: https://www.precisionmass.com/ • Address: Plot 2306, GIDC Chhatral, Ta. Kalol, Chhatral, Gujarat 382729. • Phone: 02764 233 681 • Email: sales@precisionmass.com

  17. Content Reference: • https://en.wikipedia.org/wiki/Pressure_measurement • https://www.precisionmass.com/

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