Physics
Pressure Gauges
Pressure gauges are instruments used to measure the pressure of a fluid or gas within a closed system. They typically consist of a dial or digital display that indicates the pressure in units such as pounds per square inch (psi) or pascals. Pressure gauges are commonly used in various applications, including industrial processes, automotive systems, and scientific research.
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12 Key excerpts on "Pressure Gauges"
eBook - PDFInstrument Technology
Measurement of Pressure, Level, Flow and Temperature
- E. B. Jones(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
This is, of course, a differential pressure measurement, the 'gauge pressure' being the difference between the absolute pressure of the fluid and the atmospheric pressure. Therefore: Gauge pressure = absolute pressure of fluid —pressure of the atmosphere, Absolute pressure of fluid = Gauge pressure + pressure of the atmosphere (l.la) In gauges which are sometimes spoken of as indicating vacuum or suction, they are really indicating the amount the absolute pressure of the fluid is less than atmospheric pressure, and Gauge pressure = pressure of atmosphere —pressure of fluid therefore Absolute pressure of fluid = pressure of atmosphere —Gauge pressure (1.1b) 22 MEASUREMENT OF PRESSURE In other forms of differential pressure measurement the gauge is used to measure the difference between the absolute pressures of two samples of the same fluid, or, the difference between the absolute pressures of two fluids. Figure 1.1 shows a U tube used for the various types of pressure measurement. The same principle applies when other forms of pressure measuring elements are used. 1.2 M E T H O D S OF MEASUREMENT OF PRESSURE Pressure may be measured directly in two ways. In the first place, the pressure due to a fluid may be balanced by the pressure produced by a column of liquid of known density. In the second place, the pressure may be permitted to act over a known area, and since Force Pressure = — Area or, Force = Pressure x Area, a force will be produced whose magnitude depends upon the pressure. This force may be measured by balancing it against a known weight, or, by the strain or deformation it produces in an elastic medium. Other methods of measuring pressure depend upon indirect means. Methods of measuring pressure may, therefore, be classified as follows: 1. Pressure measurement by balancing against a column of liquid of known density, Simple U tube with vertical or inclined limb, The simple U tube in practice.
eBook - PDF- Stefano Discetti, Andrea Ianiro, Stefano Discetti, Andrea Ianiro(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
SECTION II Scalar measurements CHAPTER FIVE Pressure measurements Daniele Ragni Contents 5.1 Introduction 109 The concept of pressure 109 Pressure units and standards 110 Atmospheric pressure, static pressure, and total pressure 112 5.2 Direct pressure measurement devices 118 Deadweight gauges 118 Manometers and barometers 119 McLeod gauge 123 5.3 Indirect pressure measurement devices 124 Elastic transducers 124 Bourdon tubes 124 Diaphragms 124 Strain gauges 125 Emission-based techniques: pressure-sensitive paint 127 5.4 Dynamic pressure measurements 128 Resonant transducers and vibrating cylinder 130 Microphones, capacitor type 132 Inductive and reluctive transducers 135 5.5 Some aspects on measurement procedures 136 Problems 138 Additional exercises 140 References 141 5.1 Introduction The concept The “pressure” concept is very relevant in physics and aerodynamics, since it lays the basis of pressure for the generation of fuid forces and loads on objects. “Pressure” is a derived quantity defned as force per unit area. “Force” and “area” are also derived from three fundamental quantities: “length,” “mass,” and “time”; therefore, the frst one is usually written as a combination of the last three ones. Typically, the concept of pressure is wrongly confused with the one of “force,” mainly due to the historical ways of measuring pressures by applying forces on known areas. While pressure stresses can be measured in solids by exploiting the stiffness characteristics of materials and structures, in fuids (i.e., gas and liquids) the measuring procedure is rather different. When considering fuids indeed, the movement of their constituting molecules can-not be neglected. An interesting relation can be derived, that states how the statistical kinetic motion of the molecules constituting the fuid medium can be linked to its resultant pressure.
No longer available |Learn moreVacuum
Fundamental Physics Concept (Concepts and Applications)
- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 4 Pressure Measurement The construction of a bourdon tube gauge, construction elements are made of brass Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called Pressure Gauges or vacuum gauges . A manometer could also be referring to a pressure measuring instrument, usually limited to measuring pressures near to atmospheric. The term manometer is often used to refer specifically to liquid column hydrostatic instruments. ____________________ WORLD TECHNOLOGIES ____________________ A vacuum gauge is used to measure the pressure in a vacuum—which is further divided into two subcategories: high and low vacuum (and sometimes ultra-high vacuum). The applicable pressure range of many of the techniques used to measure vacuums have an 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. Absolute, gauge and differential pressures - zero reference Although pressure is an absolute quantity, everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases measure-ments are made relative to a vacuum or to some other ad hoc reference. When distingui-shing between these zero references, the following terms are used: • Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric 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. • Differential pressure is the difference in pressure between two points. The zero reference in use is usually implied by context, and these words are only added when clarification is needed.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 2 Pressure Measurement The construction of a bourdon tube gauge, construction elements are made of brass Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called Pressure Gauges or vacuum gauges . A manometer could also be referring to a pressure measuring instrument, usually limited to measuring pressures near to atmospheric. The term manometer is often used to refer specifically to liquid column hydrostatic instruments. ________________________ WORLD TECHNOLOGIES ________________________ A vacuum gauge is used to measure the pressure in a vacuum—which is further divided into two subcategories: high and low vacuum (and sometimes ultra-high vacuum). The applicable pressure range of many of the techniques used to measure vacuums have an 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. Absolute, gauge and differential pressures - zero reference Although pressure is an absolute quantity, everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to some other ad hoc reference. When distinguishing between these zero references, the following terms are used: • Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric 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. • Differential pressure is the difference in pressure between two points. The zero reference in use is usually implied by context, and these words are only added when clarification is needed.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 2 Pressure Measurement The construction of a bourdon tube gauge, construction elements are made of brass Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called Pressure Gauges or vacuum gauges . A manometer could also be referring to a pressure measuring instrument, usually limited to measuring pressures near to atmospheric. The term manometer is often used to refer specifically to liquid column hydrostatic instruments. ________________________ WORLD TECHNOLOGIES ________________________ A vacuum gauge is used to measure the pressure in a vacuum—which is further divided into two subcategories: high and low vacuum (and sometimes ultra-high vacuum). The applicable pressure range of many of the techniques used to measure vacuums have an 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. Absolute, gauge and differential pressures - zero reference Although pressure is an absolute quantity, everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases mea-surements are made relative to a vacuum or to some other ad hoc reference. When distinguishing between these zero references, the following terms are used: • Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric 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. • Differential pressure is the difference in pressure between two points. The zero reference in use is usually implied by context, and these words are only added when clarification is needed.
eBook - PDF- D.A. Taylor(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
3 Measuring instruments The various instruments used for the measurement of different parameters and conditions are now considered. Where appropriate, the units of measurement are described and discussed. Often a particular instrument that measures one variable may be used to provide measurement of another, e.g. the measurement of differential pressure as a means of measuring liquid flow or liquid level. The most common parameters of pressure, temperature, level and flow are first described. Displacement, speed, vibration and torsion measurements then follow. General topics such as water purity, gas and oil analysis are then considered. Humidity, viscosity, photoelectric cells and fire detectors complete the instruments described. A final section deals with the testing and calibration of instruments using portable equipment. PRESSURE MEASUREMENT When a liquid or gas is in contact with a surface or boundary it exerts a force perpendicular to the surface. This force expressed in terms of a unit of area is known as pressure. The SI unit of pressure is the pascal (Pa), which is the specific name given to the derived unit of pressure, the newton per square metre (N/m 2 ). Other units commonly used for pressure measurement include the atmosphere (101.325 kPa) and the bar (100 kPa). The measurement of pressure is always relative to some particular datum. Absolute pressure is a total measurement using zero pressure as datum. Gauge pressure is a measurement above the atmospheric pressure which is used as a datum. To express gauge pressure as an absolute value it is therefore necessary to add the atmospheric pressure. A differential pressure is the difference in pressure existing between two points. Various methods of pressure measurement are used. These include the balancing of a column of liquid and the elastic deflection of various elements. 33
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 4 Pressure Measurement The construction of a bourdon tube gauge, construction elements are made of brass Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called Pressure Gauges or vacuum gauges . A manometer could also be referring to a pressure measuring instrument, usually limited to measuring pressures near to atmospheric. The term manometer is often used to refer specifically to liquid column hydrostatic instruments. ____________________ WORLD TECHNOLOGIES ____________________ A vacuum gauge is used to measure the pressure in a vacuum—which is further divided into two subcategories: high and low vacuum (and sometimes ultra-high vacuum). The applicable pressure range of many of the techniques used to measure vacuums have an 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. Absolute, gauge and differential pressures – zero reference Although pressure is an absolute quantity, everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to some other ad hoc reference. When distinguishing between these zero references, the following terms are used: • Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric 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. • Differential pressure is the difference in pressure between two points. The zero reference in use is usually implied by context, and these words are only added when clarification is needed.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 7 Pressure Measurement The construction of a bourdon tube gauge, construction elements are made of brass Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure pressure are called Pressure Gauges or vacuum gauges . A manometer could also be referring to a pressure measuring instrument, usually limited to measuring pressures near to atmospheric. The term manometer is often used to refer specifically to liquid column hydrostatic instruments. ________________________ WORLD TECHNOLOGIES ________________________ A vacuum gauge is used to measure the pressure in a vacuum—which is further divided into two subcategories: high and low vacuum (and sometimes ultra-high vacuum). The applicable pressure range of many of the techniques used to measure vacuums have an 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. Absolute, gauge and differential pressures - zero reference Although pressure is an absolute quantity, everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases mea-surements are made relative to a vacuum or to some other ad hoc reference. When distin-guishing between these zero references, the following terms are used: • Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric 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. • Differential pressure is the difference in pressure between two points. The zero reference in use is usually implied by context, and these words are only added when clarification is needed.
eBook - PDF- A. Roth(Author)
- 2012(Publication Date)
- North Holland(Publisher)
The history of low-pressure measurements is presented by Redhead (1984), while the future developments are predicted by Hobson (1984). A possible gauging method using electrostatic lévitation is discussed by Kendall et ai (1987a, b). 6.2. Mechanical gauges 6.2.1. Bourdov gauge The Bourdon gauge consists of a helical coil of hollow tubing of elliptical cross section sealed at one end and connected at the other to the vacuum system to be measured. A pointer is attached by a mechanical linkage to the free sealed end of ( § 2 ) MECHANICAL GAUGES 283 the helix and moves oyer a calibrated scale. If the pressure inside the tubing de-creases below atmospheric, the tube cross section tends to become more flat, which causes the radius of the helix to decrease, and moves the pointer. The readings of the Bourdon gauge are dependent on the pressure difference between the inside and outside of the tube thus on the external atmospheric pres-sure. Variations in atmospheric pressure can be up to 40 Torr. This limits the lower end of Bourdon gauges to about 20 Torr. 6.2.2. Diaphragm gauges Diaphragm gauges measure pressure differences by the deflection of metal (or glass) diaphragms (aneroid capsules) or bellows. The reading is amplified mechanically, optically, or electrically (capacitance, strain gauge, inductance). For the measurement of pressure in vacuum technology, the reference pressure of interest is not the atmospheric pressure, but zero, compared to the sensi-tivity range of the gauge. In the gauge shown in fig. 6.2, an evacuated beryllium-copper capsule (pressure sensitive element) is mounted in the gauge chamber, Fig. 6 . 2 Diaphragm gauge with mechanical indication. 1. Pressure sensitive element; 2. Push rod; 3. Geared sector; 4. Pinion; 5. Pointer; 6. Zero setting adjustment. Reprinted by permission of Wallace & Tiernan Ltd., Tonbridge, Kent, England. 284 MEASUREMENT OF LOW PRESSURES (CH. 6) which is connected to the system within which the pressure is to be measured.
eBook - PDFMechanical Measurements
Jones' Instrument Technology
- B E Noltingk(Author)
- 2016(Publication Date)
- Butterworth-Heinemann(Publisher)
9 Measurement of pressure E. H. HIGHAM 9.1 What is pressure? When a fluid is in contact with a boundary it produces a force at right angles to that boundary. The force per unit area is called the pressure. In the past, the distinction between mass and force has been blurred because we live in an environment in which every object is subjected to gravity and is accelerated towards the centre of the earth unless restrained. As explained in Chapter 8, the confusion is avoided in the SI system of units (Systeme International d'Unites) where the unit of force is the newton and the unit of area is a square metre so that pressure, being force per unit area, is measured in newtons per square metre and the unit, known as the pascal, is independent of the acceleration due to gravity. The relation between the pascal and other units used for pressure measurements is shown in Table 9.1. There are three categories of pressure measure-ments, namely absolute pressure, gauge pressure and differential pressure. The absolute pressure is the difference between the pressure at a particular point in a fluid and the absolute zero of pressure, i.e. a complete vacuum. A barometer is one example of an absolute pressure gauge because the height of the column of mercury measures the difference between the atmospheric pressure and the 'zero' pressure of the Torricellian vacuum that exists above the mercury column. When the pressure-measuring device measures the difference between the unknown pressure and local atmospheric pressure the measurement is known as gauge pressure. When the pressure-measuring device measures the difference between two unknown pressures, neither of which is atmospheric pressure, then the measurement is known as the differential pressure. A mercury manometer is used in Figure 9.1 to illustrate these three measurements. 9.2 Pressure measurement There are three basic methods for pressure measure-ment.
eBook - PDF- K. Diels, R. Jaeckel(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
It is, therefore, understandable that various partial pressure measuring methods have been discussed and actually are in use. One of the main features characterizing a partial pressure gauge is that — in contrast to the many designs of well-known mass spectrometers — partial Pressure Gauges form an integral part of the vacuum system. Moreover the main task of these gauges is to analyse the composition of the gas mix-ture prevailing in the vacuum system rather than to analyse gases intro-duced into the system from an outer source. Partial Pressure Gauges must be simple in design and bakeable, and should be sealed to the vacuum system with as short a connection as possible. These requirements are met by the four partial Pressure Gauges described below, and also by small cycloidal mass spectrometers. All partial Pressure Gauges can of course also be used as leak detectors. Hereby the peak of mass 32 (oxygen) usually serves as the actual leak indi-cator. In fact a partial pressure gauge, when adjusted to a fixed mass, shows features similar to a leak detector operating on the mass spectro-meter principle. Generally the sensitivity obtainable with a partial pressure gauge is less than the sensitivity of actual leak detectors. But partial pres-sure gauges show no preference for one particular search gas. The following partial Pressure Gauges seem to comply with the basic requirements : 1. Omegatron 3. Topatron 2. Farvitron 4. Mass filter after PAUL and STEINWEDEL These four gauges differ in their physical performance and their applica-tion potentialities in vacuum techniques, but are complementary to a certain degree. 1.9 PARTIAL Pressure Gauges 113 1.9.1 Omegatron Measuring range: 10 _5 -10 -11 Torr Ion sorting principle: Crossed magnetic and electrical high frequency field (similar to cyclotron). Measured quantity: Ion current. Response time: Depends on the time constant of the amplifier.
eBook - PDFOn-Line Analysis Instrument
Instrument Technology
- E. B. Jones(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
This topic is discussed in V o l u m e 1. T h e pressure of the purge gas is meas u red by a pressure gauge suited to the range of pressure to be meas u red a n d sensitive enough to show small changes of pressure. It m a y be a liquid m a n o m e t e r , a bell type instrument, or a form of bourdon tube. In the assembly used in Figure 2.1(a) a d i a p h r a g m assembly is used. O n the dial are marked two scales, one, S I , showing the total pressure and the other, S2, the portion of the pressure d u e to the specific gravity of the liquid being above unity. T h i s second scale m a y be calibrated in terms of density, specific gravity, or any other convenient hydrometer units. W h e r e the level of the liquid m u s t be allowed to vary, or where the sampling device cannot be maintained at atmospheric pressure, the a r r a n g e m e n t shown in Figure 2.1(b) is used. T w o stand pipes are immersed in the liquid so that the Figure 2.1 Stand pipe methods (Courtesy Negretti and Zambra Ltd.) 38 M E A S U R E M E N T OF D E N S I T Y O R S P E C I F I C G R A V I T Y 39 lower end of one is at a d e p t h D below the end of the other, a n d so that the level of the end of the shorter stand pipe is below the m i n i m u m level of the tank liquid. Gas is fed to both stand pipes, at rates which are constant, small, a n d equal to each other, through the restrictions R l and R2, the difference between the pressures built up in the pipes being m e a s u r e d by a suitable differential pressure gauge. T h i s pressure difference is equal to the pressure due to a column of liquid of d e p t h D, and is shown on scale SI; while the portion of the pressure due to the changes in specific gravity above some fixed value is shown on scale S2. Figure 2.2 Control system using a pneumatic amplifier (Courtesy Negretti and Zambra Ltd.) W h e r e it is required to m e a s u r e small variations of specific gravity the a r r a n g e m e n t shown in Figure 2.1(c) is used.
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