por What are the instruments to measure the pressure?
The instruments to measure pressure They are devices made of different materials that measure the force that a fluid is capable of exerting on a surface, taking atmospheric pressure as a reference. That change is recorded on a calibrated scale or display, and is expressed in units of pressure.
The units of measure in which pressure is expressed indicate a unit of force over a unit of area.
Although the standard unit of measurement is the Pascal (N/m2), it is also measured in pounds per square inch (PSI), in atmospheres (atm), in kilograms per square centimeter (kg/cm²), inches of mercury (Hg) and millimeters of mercury (mm Hg).
It is worth saying that the pressure is the force per unit area. It is experienced when that force is perpendicular to the surface.
pressure types
The different types of pressure are:
Of emptiness.
Absolute.
Dynamic.
static.
atmospheric.
Manometric.
Differential.
barometric.
Stagnation.
There are various instruments for measuring pressure and although most are used to measure relative pressure, there are some designed to measure absolute pressure.
List of instruments for measuring pressure
1. Differential pressure gauge
It is also known by the name of a manometer with two open branches. It is a device used to measure the difference in pressure between two places.
The fluid used by the differential manometer to indicate the values can be any liquid: water, kerosene, alcohol, among others. The essential condition is that it does not mix with the fluid that is under pressure.
If you are trying to measure high pressures or very large pressure differences, the liquid should be very dense. Mercury is often used in these cases.
In a manometer, the measurements can go from 0 to 0.5 KPa (≈ 0.2”H₂O); or from 0 to 7000 KPa (≈ 1000 psi).
2. Truncated manometer
It is a type of manometer that is used to measure small gas pressures. It measures absolute pressures and has shorter branches than the differential.
3. Vacuum gauge
It is a device used to measure vacuum, that is, to measure pressures below atmospheric pressure.
It turns out to be a very useful tool in refrigeration plants or where liquefied gases are worked, because the critical points of gases and steam are calculated based on absolute temperatures and pressures.
Although the measurement range depends on the material from which it is made, it can cover measurements between -0.5 and 0 KPa; and -100 to 0 KPa (≈ -30 to 0 “Hg).
Some of the types of vacuum gauges are:
McLeod vacuum gauge
It is an analog vacuum gauge with direct reading quadratic scale.
piston-cylinder
It is a primitive method of measuring pressure known as a pressure or dead weight balance.
It consists of scales that have a vacuum chamber that is placed on top to eliminate the air buoyancy correction.
4. Pressure sensors
Pressure sensors are devices designed to subject materials to a pressure that deforms them in their elastic range. Such deformation is proportional to the pressure used and is considered linear.
In this way, pressure sensors transform pressure into displacement. The sensor then converts the movement into an electrical signal, such as voltage or current.
The most universal pressure transducers are:
The strain gauge.
Variable Capacitors.
The piezoelectric.
5. U-tube
It consists of a glass tube bent into a U shape, which is partially filled with a liquid of known density.
One end of the tube is connected to the object or space in which you want to measure the pressure, while the other end is left free.
The pressure exerted at the end where there is high pressure will cause the movement of the liquid inside the tube.
This movement will be reflected in a difference in level (or height) marked as h, and which depends on the pressure and density of the liquid in the tube.
6. Bourdon tube
It is a device with a metallic and elastic tube, which is flattened and curved in a special way. When pressure is applied, the tube straightens and its free end moves.
It is this movement that moves the levers and gears, which end up moving a needle that indicates the pressure on the scale.
7. Bellows
This instrument has an elastic component in the form of a bellows or accordion, to which the pressure to be measured is applied.
By applying pressure, the bellows stretches and it is this movement that moves the measurement needle.
8. Diaphragm pressure gauge
This instrument is a variant of the bellows manometer. It has the shape of a disk to which concentric circular corrugations are made.
In this device, the pressure is exerted on an elastic diaphragm, whose deformation results in the movement of the pointer indicating the measurement.
The diaphragm can also be metallic, in which case it uses the elastic characteristic of the material to be measured.
This type of gauge is used to measure low differential pressures or vacuum pressures.
9. Barometer
It is the instrument used to measure atmospheric pressure. There are several types of barometers:
Torricelli tube
It bears that name in honor of its inventor, Evangelista Torricelli, who devised it in 1643.
It consists of a tube 850 mm long which is closed at the top and kept open at the bottom to be filled with mercury. The level of this liquid metal is what indicates the pressure there is.
Fontini Barometer
It is the improved version of the Torricelli tube and is used in weather stations to obtain very precise measurements and on different scales.
metallic barometers
It is a type of barometer that works with gas, so it is less sensitive than mercury, but it is practical.
Altimeter
It is the type of metallic barometer used to measure altitude above sea level.
Aneroid barometer
It is a cylinder with elastic walls that measures variations in atmospheric pressure.
10. Sphygmomanometer or tensiometer
It consists of an inflatable cuff, a manometer, and a stethoscope that allows indirect measurement of blood pressure, by listening to Korotkov sounds.
It can work with mercury or air and requires the use of a stethoscope or stethoscope.
There is a variant of this device that is electronic. It is accurate and very easy to use, which is why it has become very popular. It is a device that is very sensitive to noise and movement.
11. Pitot tube
It is an instrument to measure the speed of the wind, and industrial gases. In conjunction with the barometer, it is useful to accurately know the atmospheric conditions.
References
Dulhoste, JF Pressure measurement. Retrieved from webdelprofesor.ula.ve.
Units and instruments to measure pressure. Recovered from lapresion.wikispaces.com.