Extra Sight Pin
Pressure measurement
Absolute, gauge and differential pressures - Null Reference
Although pressure is an absolute quantity, everyday pressure measurements, such as tire pressure, are usually made relative to ambient pressure. In other cases, measurements made relative to a vacuum or some other ad hoc reference. If the distinction between these zero references, The following terms are used:
Absolute pressure is zero referenced against a perfect vacuum, it is equal to atmospheric pressure plus gauge.
Gauge pressure Reference is made to zero atmospheric pressure, it is equal to absolute pressure minus atmospheric pressure. Negative symptoms are usually omitted.
Differential pressure is the pressure difference between two points.
The zero-reference in use is usually implied by the context, and these words are only added when clarification is needed. Tire pressure and blood pressure by convention, while atmospheric pressure, low vacuum pressure, pressure and altimeter must be absolute. Differential pressures are often in the industrial use Process Systems. Differential pressure gauges have two inlet openings, each with one of the volumes to monitor the pressure. In effect, such a doctrine, the mathematical operation of subtraction through mechanical means, so that observing no need for an operator or control system in two separate gauges and To determine the difference in readings. Moderate vacuum pressures are often ambiguous because they can represent absolute pressure or gauge pressure, without a negative sign. Such a vacuum 26 Gauge inHg an absolute pressure of 30 inHg (typical atmospheric pressure) 26 inHg = 4 inHg.
The air pressure is usually about 100 kPa at sea level, but with the amount is variable and weather. If the absolute pressure of a liquid remains constant, the pressure of the same fluid pressure changes varies. For example, if a car runs a mountain, go on the tire pressure. Some standard values of atmospheric pressure and as 101.325 kPa or 100 kPa have been defined, and some instruments in a The following standard values as a constant zero reference instead of the actual variable ambient air pressure. This affects the accuracy of these instruments, especially when in high altitudes used.
Use of the atmosphere as a reference in a rule by one (called g), after the pressure unit eg 30 psi g, which means that the measured pressure is the total pressure minus atmospheric pressure. There are two types of gauge reference pressure: vented gauge (vg) and sealed gauge (SG).
A ventilated Pressure transmitter, for example, allows the outside air pressure on the negative side of the pressure sensing diaphragm are exposed through a cable or a vent hole on the Side of the device so that it always measures the pressure to ambient pressure. So a vented gauge reference pressure sensor should always be at zero pressure when the process pressure connection is kept open to the air.
A sealed gauge reference is very similar, except that atmospheric pressure sealed on the negative side of the membrane. This is usually adopted at high pressure areas such as hydraulics, where atmospheric pressure changes will have no significant impact on the accuracy of the reading, so ventilation is not necessary. This also allows for some producers provide secondary pressure containment as an extra precaution for pressure equipment when the safety burst the primary pressure sensing diaphragm is exceeded.
There is another way of creating a sealed gauge reference, and this is a high negative pressure to the Back of the sensor diaphragm. Then the output signal thus compensating the pressure sensor reads close to zero in the measurement of atmospheric pressure.
A sealed gauge reference Pressure sensor will never read exactly zero because atmospheric pressure always changed and the reference in this case is fixed at 1 bar.
An absolute pressure measurement is one of the absolute Vacuum is known. The best example of an absolute pressure reference or atmospheric pressure.
To produce an absolute pressure sensor is one of the manufacturers high vacuum behind the sensing diaphragm. If the process pressure connection of an absolute pressure transmitter is open, the air is, reads the actual air pressure.
Units
Pressure Units
pascal
(Pa)
Bar
(Bar)
technical atmosphere
(At)
Atmosphere
(Atm)
Torr
(Torr)
Pound-force per
Square inch
(Psi)
1 Pa
1 N/m2
105
1.0197105
9.8692106
7.5006103
145.04106
1 bar
100 000
106 dyn/cm2
1.0197
0.98692
750.06
14.5037744
1 at
98,066.5
0.980665
1 kgf/cm2
0.96784
735.56
14.223
1 atm
101 325
1.01325
1.0332
1 atm
760
14.696
1 Torr
133.322
1.3332103
1.3595103
1.3158103
1 Torr; 1 mmHg
19.337103
1 psi
6.894103
68.948103
70.307103
68.046103
51.715
1 lbf/in2
Example reading: 1 Pa = 1 N/m2 = 105 bar = 10.197106 = 9.8692106 at ATMs, etc.
The SI unit for pressure is Pascal (Pa), equal to one Newton per square meter (or Nm2 kgm1s2). This special name for the device was taken in 1971, before that the pressure in SI units was expressed as N / m. If specified, the zero reference is in brackets after the unit, for example 101 kPa (ABS). The pound per square inch (psi) is still widespread in the United States, Canada, especially for cars. A letter is often appended to the PSI unit, the measurement of the zero-reference specified; psia for absolute, psig for Gauge, psid for differential, although this practice is discouraged by the NIST.
Because pressure was commonly measured by its ability to provide a column of fluid to displace in a pressure gauge, are often expressed as a pressure at a depth of a particular fluid (eg inches of water). The most common choice is mercury (Hg) and water, water is nontoxic and readily available, while mercury density allows a shorter column (and thus a smaller manometer) to a certain pressure to measure.
Fluid density and local gravity can vary from one reading to another depending on local conditions, so that the amount of a liquid column not precisely defined pressure. As "millimeters of mercury or inches of mercury 'are quoted today, these devices are not on a physical Mercury, but they were precise definitions that can be expressed in terms of SI units given. The marine units usually assume one of the older Definitions of the kilogram as the weight of one liter of water.
Although not by measurement specialists are favored, these units still manometric you in many areas. Blood pressure is measured in millimeters of mercury in many parts of the world, and lung pressures in centimeters of water are still widespread. Natural gas pipeline pressures measured in inches of water, expressed as "WC" ("Water Column). divers often applies a manometric rule of thumb: the pressure exerted by ten meters of water usage is approximately equal to one atmosphere. In vacuum systems, units, micrometers torr of mercury (micron) and inches of mercury (inHg) are used most often. Torr and Micron normally shows a absolute pressure, while inHg usually a positive pressure.
Atmospheric pressure are generally using kilopascals (kPa), or atmospheres (atm), with Except in American meteorology where the hectopascals (hPa) and millibars (mbar) are preferred. In American and Canadian engineering, stress is often measured in kip. Note That stress is no real pressure, because it is not scalar. In the CGS system the unit of pressure, the barye (BA), was equal to 1 dyncm2. In the MTS system, the unit was for the Pressure of Piez, like Demosthenes 1 per square meter.
Many other hybrid units such as mmHg / cm or grams-force/cm (sometimes as kg / cm and without proper g/mol2 Determination of combined units used). With the name kilogram, gram, kilogram-force, or gram-force (or their symbols) as a unit of force prohibited in SI, the unit of Force in SI is the Newton (N).
Static and dynamic pressure
Static pressure uniformly in all directions, so pressure measurements are independent of the direction in a immovable (static) liquid. Flow, however, applies additional pressure on surfaces perpendicular to the flow direction, while only a minor effect on surfaces parallel to the flow direction. This directional component of pressure in a moving (dynamic) fluid is called dynamic pressure. An instrument before Flow direction measures the sum of the static and dynamic loads, this measurement is defined as the total pressure and dynamic pressure. Since dynamic pressure is referenced to static pressure, It is measured nor absolute, it is a differential pressure.
While static pressure is of primary importance in determining net loads on pipe walls, dynamic Pressure is used for measuring the flow rates and airspeed. Dynamic pressure is the pressure difference between instruments measured parallel and perpendicular to the flow direction be. Pitot-static tubes, for example, perform this measurement on airplanes to determine airspeed. The presence of the meter to flow inevitably acts distract and create turbulence, so his form is crucial for the accuracy and the calibration curves are often non-linear.
Applications
Altimeter
Barometer
MAP Sensor
Pitot tube
Blood Pressure Monitor
Instruments
Many instruments have been invented to measure pressure, with different advantages and disadvantages. Pressure range, sensitivity, dynamics and cost all depending on several orders of magnitude from one instrument to the next design. The oldest form is the liquid column (Filled a vertical tube with mercury) manometer invented by Evangelista Torricelli in 1643. The U-tube was invented by Christian Huygens in 1661.
Hydrostatic
Hydrostatic gauges (such as the mercury manometer to compare), the hydrostatic pressure, force per unit area on the basis of a liquid column. Hydrostatic gauge measurements are measured independently of the nature of the gas is, and can have a very linear calibration. They have poor dynamics.
Piston
Piston gauges Counterweight to the pressure of a liquid with a solid weight or a spring. Another name for piston gauge is pressure scale. For example, dead-weight tester for the Calibration or tire pressure gauges used.
Liquid column
The difference in height of the liquid in a liquid column manometer is proportional to the pressure difference.
Liquid column gauges consist of a vertical column of liquid in a tube, the ends in different strains suspended. The column will rise or fall until its weight is in equilibrium with the pressure difference between the two ends of the tube. A very simple version is a U-shaped Pipe half full of liquid, one side is the region of interest while connected to the reference value of pressure (which is perhaps the atmospheric pressure or vacuum) be applied with the other. The difference in the liquid represents the applied pressure. The pressure exerted by a liquid column of height h and the density is determined by the hydrostatic pressure equation P = hg. Therefore, can the pressure difference between the applied pressure Pa and the reference pressure P0 in a U-tube manometer by loosening Pa P0 = hg be found. If the liquid is measured much more dense, hydrostatic corrections may have for the height between the moving surface be made of the manometer working fluid and the place where the pressure measurement is desirable.
Although any liquid can be used for mercury its high density (13.534 g / cm 3) and low vapor pressure, preferably pressure. For low pressure differences well above the vapor pressure of water, water is often used (And "inches of water is a common pressure unit). Liquid-column manometers are independent of the type of gas is measured and have a very linear calibration. You have poor dynamics. In measuring the vacuum, the liquid can evaporate and contaminate the vacuum to work when its vapor pressure is too high. In the measurement of liquid Pressure, a loop with a gas or a liquid filled light must isolate the liquids, to prevent them from mingling. Simple devices can measure hydrostatic pressures in the range of a few Torr (a few 100 Pa) to several atmospheres. (Approximately 1,000,000 Pa)
A single leg-liquid-column manometer has a larger Tank instead of the one side of the U-tube and has a scale beside the narrower column. The column may be inclined to further enhance the fluid movement to be. Based on the use and the structure on the type of pressure gauge are
Simple Manometer
Micromanometer
Differential Pressure Meter
Inverted differential manometer
A pressure gauge McLeod, mercury discharged
McLeod gauge
A McLeod gauge isolates a sample of gas to and condenses them into a modified mercury manometer until the pressure only a few mmHg. The gas must be well-behaved during its compression (it must not condense, for example). The technique is slow and not suitable for continuous monitoring, but is capable of good accuracy.
Related Coverage: 4:10 Torr (about 10-2 Pa) as high as 106 Torr (0.1 MPa)
0.1 MPa, the lowest direct Measuring pressure, which is possible with current technology. Other vacuum gauges can measure lower pressures, but only indirectly by measuring pressure-controlled other properties. These indirect measurements must be calibrated to SI units via a direct measurement, usually measured by a McLeod.
Aneroid
Aneroid instruments based on a metallic pressure sensing element that bends elastically under the action of a pressure difference on the element is based. "Aneroid" means "without liquid, "And the term originally distinguished these gauges from the hydrostatic gauges described above. However Aneroid instruments used to the pressure of a liquid to measure and a gas to be, and they are not the only form of teaching that can be operated without liquid. For this reason, they are often called mechanical gauges in the modern Language. Aneroid gauges are not measured depending on the type of gas is, in contrast to thermal ionization and teachings, and are less likely to make the system as a hydrostatic Teacher-contaminate. The pressure sensor element is a Bourdon tube, a diaphragm, a capsule or a set of bellows, which is the shape of the response to the pressure of the region change. The deflection of the pressure sensing element can be connected by a rod with a needle or read can be read from a secondary sensor. The most common secondary transducers in modern vacuum gauges measure a change in capacity of the mechanical deformation. Gauges which rely on a change in capacity are often called Baratron gauges.
Bourdon
Diaphragm Pressure Gauge
A Bourdon gauge uses a coiled tube, which, as it expands due to increase pressure causes a rotation of the arm is connected to the tube. In 1849 the Bourdon tube pressure gauge was patented in France by Eugene Bourdon.
The pressure sensor element is a closed Coiled tube at the chamber or tube is connected to the pressure felt. As the pressure increases the tube will tend to uncoil, while a reduced pressure will cause the tube to coil more tightly. This movement is connected by a link with a transmission counter is a transfer needle. The needle is in front of a card to the Picture with the inscription pressure indications presented in particular in connection with needle deflections. In a barometer, the Bourdon tube at both ends and the absolute pressure of the surrounding Sealed atmosphere is felt. Differential Bourdon gauges use two Bourdon tube and a mechanical linkage that compares the measured values.
In the following figures the transparent cover face of the depicted combination pressure and vacuum gauge was removed and the mechanism from the housing to be removed. This particular gauge is combination vacuum and pressure gauges for automobile diagnosis:
Indicator page with map and Dial
Mechanically page Bourdon Tube
the left side of the face, to measure using the vacuum manifold, is calibrated in inches of mercury on its inner circumference and the inches of mercury on its outer scale.
the right part of the face is used to measure fuel pump pressure and is calibrated in fractions of 1 kg / cm on its inner circumference and pounds per square inch on its outer scale.
Mechanically Details
Mechanical Details
Stationary parts:
To A: Receiver block. This connects the cable to the fixed end of the tube spring (1) and secures the base plate (B). The two holes receive screws that secure the case.
B: Chassis plate. The image map is attached. It contains holes for Axes.
C: Secondary base. It supports the outer ends of the axles.
D: Reviews and space to connect the two chassis plates.
Mobile Parts:
Stationary end of Bourdon tube. This communicates with the intake manifold of the recipient block.
Moving end of Bourdon tube. This end is sealed.
Pivot and cones.
Add link pin on the lever (5) with pins to allow joint rotation.
Lever. This expansion of the sector gear (7).
Sector gear axle PIN.
Sector gear.
Indicator needle axis. This has a spur gear that the sector gear (7) engages and extends through the face on the indicator needle drive. Due to the short distance between the lever arm link boss and the pivot pin and the difference between the effective radius of the sector gear and the spur gear, any motion the Bourdon tube is greatly enhanced. A small movement of the tube leads to a great movement of the indicator needle.
Hair spring preload the gear to gear to Lash and eliminate hysteresis.
Diaphragm
A bunch of pressure capsules with corrugated diaphragms in an aneroid barograph.
A second type of aneroid gauge uses the Deflection flexible membrane that separates different regions of the pressure. The deflection is repeatable for known pressures so the pressure by calibration can be determined. The deformation a thin membrane is dependent on the pressure difference between the two faces. The reference face can open atmosphere gauge measuring pressure, open to a second port to measure differential pressure, or can measure are sealed against a vacuum or other fixed reference pressure, absolute pressure. The deformation measured by means of mechanical, optical or capacitive techniques. Ceramic and metallic membranes are used.
Useful range: above 10-2 Torr (about 1 Pa)
For absolute measurements, welded Pressure capsules with diaphragms on both sides are often used.
Form:
Apartment
wavy
flattened tube
Capsule
Bellows
In small equipment for pressure or pressure differences, or require that a measure absolute pressure sense, the transmission and needle are driven by a closed and sealed chamber Bellows, called an aneroid, which means "without liquid". (Early barometers used a column of liquid such as water or the liquid metal mercury exposed through a vacuum.) This bellows configuration is used in aneroid barometer (barometer with an indicating needle and dial-up card), altimeters, altitude record Barograph, and the level-telemetry instruments used in weather balloon radiosondes. These devices use the sealed chamber as the reference pressure and are due to pressure from the outside driven. Other sensitive aircraft instruments such as indicators and airspeed indicators, rate of climb (vertical speed) connections, both for the internal part of Aneroid chamber and an external chamber surrounds.
Electronic pressure sensors
Main article: Pressure sensor
Piezoresistive strain gauges
Uses the piezoresistive Effect of bonded strain gauges or made to be seen by loads applied pressure.
Capacitive
Uses a diaphragm and pressure to create voids to a variable capacitor charge to recognized by applied pressure.
Magnetic
Measures the deflection of a membrane by changes in inductance (reluctance) LVDT, Hall effect, or by eddy current client.
Piezoelectric
Uses the piezoelectric effect in certain materials such as quartz measuring the load on the sensing mechanism by pressure.
Optical
Used to detect the physical change of an optical fiber burden of applied pressure.
Potentiometric
Uses the motion a windshield wiper along a resistive mechanism for determining the burden of the applied pressure causes.
Resonant
Uses the changes in the resonant frequency measured in a stress-sensing mechanism or changes in the gas density, caused by pressure applied.
Thermal conductivity
Overall, as a real gas rises in the density can show, what a question of increasing pressure their ability to heat increased. With this type of ad, a wire filament is by running electricity through they are heated. A thermocouple or Resistance Temperature Detector (RTD) can then be used to measure the temperature of the filament. This temperature depends on the speed with the filament loses heat to the surrounding gas, and thus on the thermal conductivity. A common variant is the Pirani, which uses a single platinum filament, as both the heated element and RTD. These devices are 10-103 Torr Torr accurate, but they are sensitive to the chemical composition of the exhaust gases measured.
Two wire
A wire coil is used for heating, and the other is used to measure nearby temperature due to convection.
Pirani (one wire)
A Pirani consists of a open metal wire, the pressure is measured. The wire is heated by a current flows through and cools the surrounding gas. If the gas pressure is reduced, the cooling reducing effect, so that the balance will increase temperature of the wire. The resistance of the wire is a function of temperature: by measuring the voltage across the wire and the current through them, the resistance (and thus the gas pressure) can be determined. This type of gauge was invented by Marcello Pirani.
Thermocouple gauges and thermistor gauges Work in a similar way, except is a thermocouple or thermistor used to measure the temperature of the wire.
Useful range: 10-3 - 10 Torr (about 1:10 - 1000 Pa)
Ionization gauge
Ionization gauges are the most sensitive gauges for very low pressures (also referred to as "hard or high vacuum). You feel pressure indirectly by measuring the electrical ions produced when the gas is bombarded with electrons. Fewer ions will be produced by lower density gases. The calibration an ion gauge is unstable and dependent on the nature of the measured gases, which is not always known. You can play against a McLeod gauge, the more stable and is independent calibration of gas chemistry.
Thermionic emissions generated electrons collide with gas atoms and positive ions. The ions are a accordingly biased electrode known as a collector dressed. The current in the collector is proportional to the rate of ionization, which is a function of pressure in the system. The measurement the collector current gives the gas pressure. There are various subtypes of the measured ionization.
Useful range: 10-10 - 10-3 torr (about 10-8 - 10-1 Pa)
Most ion gauges into two types: hot cathode and cold cathode, a third kind that is more sensitive and expensive known as the spinning rotor gauge, but is not discussed here. In the hot Cathode version an electrically heated filament produces an electron beam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected with a negative electrode. The current depends on the number of ions, which depends on the pressure in teaching. Hot cathode gauges are accurate up from 103 Torr 1010 Torr. The principle behind cold cathode version is the same, except that electrons generated in a discharge by a high voltage electric discharge generated. Cold cathode gauges are exactly the 102-109 Torr Torr. Ionization Gauge Calibration is very sensitive to construction geometry, chemical composition of gases is measured, Corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low pressure. The composition of gases at high vacuum will be unpredictable in general, a mass spectrometer must be used in conjunction with the ionization gauge for an accurate measurement.
Hot Cathode
Bayard-Alpert Hot cathode ionization gauge
A hot cathode ionization gauge is mainly composed of three electrodes all as a triode, where the cathode is the filament. The three electrodes are a collector or plate, a thread, and a grid. The collector current is measured in picoamps by an electrometer. The heating voltage to ground is usually at a Potential of 30 volts while the voltage to 180 210 volts DC, unless there is an optional feature, electron bombardment, by heating of the lattice, the high potential have approximately 565 volts. The most common ion gauge is the hot cathode Bayard-Alpert gauge, with a small ion collector inside the grid. A glass envelope with an opening to the vacuum can surround the electrodes, but generally the Nude Gauge is inserted directly into the vacuum chamber, where the pins through a ceramic plate fed in the wall of the chamber. Hot cathode gauges can be damaged or lose their calibration when they are at atmospheric pressure or even low vacuum are exposed to hot. The measurements of a hot cathode ionization gauge is always logarithmic.
Electrons emitted from the filament move several times back and forth movements around the Grid before it finally on the grid. During these movements, some electrons collide with a gaseous molecule, a pair of an ion and an electron (Electron Ionization). The number of these ions is proportional to the density of gaseous molecules, the electron emitted multiplied by the current from the filament and these ions flow into the collector to an ion current form. Since the gaseous molecule density is proportional to the pressure of the pressure by measuring the ionic current is estimated.
The low sensitivity Hot cathode gauges is limited by the photoelectric effect. The electrons hit the grid produce x-rays to produce photoelectric noise in the ion collector. This limits the range of older hot cathode gauges to 108 Torr and the Bayard-Alpert to about 1010 Torr. Additional wires at cathode potential in the line of sight between the collector and the lattice ions to prevent this effect. In the extraction of the ion type are not attracted by a wire, but by an open cone. Since the ions do not decide can take which part of the cone, they go through the hole and form an ion beam. This ion beam can be passed, a
Faraday Cup
Microchannel plate Detector with Faraday cup
Quadrupole mass analyzer with Faraday cup
Quadrupole mass analyzer with a microchannel plate detector Faraday cup
Ion lens and acceleration voltage and aimed at a target at a sputtering gun. In this case a valve lets gas into the net cage.
See also: electron ionization
Cold cathode
There are two subtypes of cold-cathode ionization gauges: the Penning gauge (invented by Frans Michel Penning), and measure the inverted magnetron, also known as Redhead. The main difference between the two is the position of the anode with respect to the cathode. Neither has a filament, and each may require a DC potential of about 4 kV for operation. Inverted magnetrons can to 1x1012 Measure Torr.
Such lessons can not function if the ions from the cathode recombine before reaching the anode produced. If the mean free path of the gas- within the track width is smaller than the dimensions of the gauge, then the electrode current will essentially vanish. A practical upper bound on the detectable pressure is, for a Penning gauge, of the order of 103 Torr.
Similarly, cold cathode gauges are reluctant at very low pressures Start, that the near-absence of a gas makes it difficult to establish a current electrode - especially in Penning gauges which use an axisymmetric magnetic field to path lengths for ions in the order to create of meters. In the air suitable ion pairs are formed by ubiquitous cosmic radiation in a Penning gauge design features are used to the set-up of the discharge is to pave way. For example, the electrode of a Penning gauge is usually finely tapered to facilitate the field emission of electrons.
Maintenance cycles of cold cathode gauges are in is usually measured in years, depending on the type of gas, the pressure that they are operated in. Using a cold cathode gauge in gases with substantial organic components, such as Pump oil fractions can result in the growth of delicate carbon films and pieces in the theory that eventually either short-circuit the electrodes of the gauge, or impede the generation of a discharge path.
Calibration
Gauges are either direct or indirect-reading. Hydrostatic and elastic pressure gauge to measure pressure directly by Violence on the surface by incident particle flux affects exercised, and be as direct reading gauges. Thermal ionization gauges read pressure indirectly and through the Measuring a gas property that changes in a predictable way, with gas density. Indirect measurements are susceptible to more errors than the direct measurements.
Tare Tester
McLeod
Ionization mass spectrometry +
Dynamic transients
If the liquid does not flow in equilibrium, local pressures higher or lower than the average pressure in a medium. These disturbances propagate from their source as longitudinal pressure variations along the path of propagation. This will also as sound. Sound pressure level is the instantaneous local pressure deviation from the average pressure caused by a sound wave. Sound pressure level measured with a microphone in the air and a hydrophone in the water are. The effective sound pressure level is the root mean square of the instantaneous sound pressure in a given time interval. Sound pressure levels are usually small and are often expressed in units of Microbar.
Frequency response of pressure sensors
Resonance
History
Further information: Timeline of temperature and pressure measurement technology
European (CEN) Standard
EN 472: Pressure gauge - vocabulary.
EN 837-1: Pressure gauge. Bourdon tube. Dimensions, metrology, requirements and testing.
EN 837-2: manometer. Selection and installation of pressure gauges.
EN 837-3: Pressure gauge. Diaphragm and capsule pressure gauges. Dimensions, metrology, requirements and tests ..
See also
Force gauge
Piezometer
Vacuum technology
External Links
Home Made Manometer
Manometer
References
^ NIST
^ Was ["fluidengineering.co.nr / Manometer.htm. At 1 / 2010, which took me to a bad connection. Type of fluid pressure gauge]
^ Techniques the high vacuum
^ Beckwith, Thomas G., Roy D. Marangoni and John H. Lienhard V (1993). "Measurement of low pressure." Mechanical Measurements (fifth ed.) Reading, MA: Addison-Wesley. pp. 591 595. ISBN 0-201-56947-7.
^ Product brochure from Schoonover, Inc
^ VG Scienta
^ Robert M. Besanon, ed (1990). "Vacuum Techniques "(3rd edition ed.) Van Nostrand Reinhold, New York. Pp. 12,781,284. ISBN 0-442-00522-9.
Wikimedia Commons to: gauge
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