Measurement of Atmospheric Pressure

Barometric Measurement

• Atmospheric pressure is measured using a barometer, which is a device that measures the weight of the air column above it.
• The most common type of barometer is the mercury barometer, which consists of a sealed tube filled with mercury.
• The mercury column rises or falls in response to changes in atmospheric pressure, allowing the pressure to be measured.

Manometer Calibration

• A manometer is a device used to measure the pressure difference between two points in a fluid system.
• Calibration of a manometer involves setting the zero point of the instrument to match the atmospheric pressure at the location.
• This is done by adjusting the manometer to read zero when the pressure on both sides of the instrument is equal to the atmospheric pressure.

Fluid Column Manometry

• Fluid column manometry is a method of measuring pressure using a column of fluid (such as water or mercury) of known density.
• The pressure is measured by determining the height of the fluid column, which is proportional to the pressure.
• The formula for calculating pressure using fluid column manometry is: P = ρgh, where P is the pressure, ρ is the density of the fluid, g is the acceleration due to gravity, and h is the height of the fluid column.

Pressure Units Conversion

• Pressure units can be converted between different systems using the following conversion factors:
  • 1 atm = 1013.25 mbar = 101.325 kPa = 760 mmHg
  • 1 psi = 6.89476 kPa = 51.715 mmHg
  • 1 mbar = 0.1 kPa = 0.75 mmHg
• It is important to be able to convert between different pressure units to ensure accurate communication and comparison of data.

Absolute Pressure

• Absolute pressure is the pressure measured relative to a perfect vacuum (0 psia).
• It is the sum of the atmospheric pressure and the gauge pressure.
• The formula for calculating absolute pressure is: P_abs = P_atm + P_gauge, where P_abs is the absolute pressure, P_atm is the atmospheric pressure, and P_gauge is the gauge pressure.
• Absolute pressure is important in engineering and scientific applications, as it provides a reference point for pressure measurements.