Pressure is measured by determining the force exerted per unit area on a surface. The standard unit for measuring pressure is the pascal (Pa), which is equivalent to one Newton per square meter (N/m²).
Methods for Measuring Pressure
Various instruments and techniques are employed to measure pressure, depending on the application and pressure range. Some common methods include:
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Manometers: These devices use liquid columns (typically mercury or water) to measure pressure differences. The height of the liquid column is proportional to the pressure.
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Barometers: Used specifically to measure atmospheric pressure. A common type is the mercury barometer, where atmospheric pressure supports a column of mercury.
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Pressure Gauges: These are instruments that directly indicate pressure on a dial or digital display. Common types include:
- Bourdon tube gauges: Utilize a curved tube that deflects proportionally to the pressure applied.
- Diaphragm gauges: Employ a flexible diaphragm that deflects under pressure.
- Strain gauge pressure sensors: Use strain gauges bonded to a diaphragm or other pressure-sensitive element to measure deformation caused by pressure. The change in resistance of the strain gauge is proportional to the applied pressure.
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Pressure Transducers: These devices convert pressure into an electrical signal. They are often used in automated systems and data acquisition applications.
Units of Pressure
While the pascal (Pa) is the SI unit, other units are commonly used:
- psi (pounds per square inch): Frequently used in the United States.
- torr: Often used in vacuum applications.
- bar: A metric unit close to atmospheric pressure.
- Atmosphere (atm): Approximately equal to the average atmospheric pressure at sea level.
Example
Imagine inflating a tire. A pressure gauge attached to the tire valve measures the air pressure inside the tire. This gauge might display the pressure in psi (pounds per square inch). The gauge works by converting the pressure inside the tire into a mechanical movement, which is then translated into a reading on the dial.
In summary, pressure is quantified by measuring force per unit area. Various instruments, employing different physical principles, are used for this purpose, and the results are often expressed in a variety of units.
