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change the vapor pressure, for temperature and altitude effects on the weight of mercury, and for
deviations from standard gravity (9.80665 m/s
2 or 32.17405 ft/s
2 ). Correction curves are provided
by instrument manufacturers.
Barometers are used as local standards for the measurement of absolute atmospheric pressure.
Under standard conditions for pressure temperature and gravity, the mercury rises 760 mm (29.92
in.) above the reservoir surface. The U.S. National Weather Service always reports a barometric
pressure that has been corrected to sea-level elevation.
Manometer
A manometer is an instrument used to measure differential pressure based on the relationship
between pressure and the hydrostatic equivalent head of fluid. Several design variations are
Glass cylinder
reservoir
Zeroing
pointer
Adjusting
screw
Mercury vapor at
vapor pressure
Closed end
Meniscus
Liquid
mercury
Glass
tube
Scale
Figure 9.4 Fortin barometer.
380 Chapter 9 Pressure and Velocity Measurements
15:4:52 Page 380
change the vapor pressure, for temperature and altitude effects on the weight of mercury, and for
deviations from standard gravity (9.80665 m/s
2 or 32.17405 ft/s
2 ). Correction curves are provided
by instrument manufacturers.
Barometers are used as local standards for the measurement of absolute atmospheric pressure.
Under standard conditions for pressure temperature and gravity, the mercury rises 760 mm (29.92
in.) above the reservoir surface. The U.S. National Weather Service always reports a barometric
pressure that has been corrected to sea-level elevation.
Manometer
A manometer is an instrument used to measure differential pressure based on the relationship
between pressure and the hydrostatic equivalent head of fluid. Several design variations are
Glass cylinder
reservoir
Zeroing
pointer
Adjusting
screw
Mercury vapor at
vapor pressure
Closed end
Meniscus
Liquid
mercury
Glass
tube
Scale
Figure 9.4 Fortin barometer.
380 Chapter 9 Pressure and Velocity Measurements