Download Fluid Pressure Measurement

Fluid Pressure
Measurement
How is pressure generated?
 Pressure is force divided by the area over which the force
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acts.
For a fluid in a pressure vessel, the molecules colliding
with the walls cause the force.
Molecules change linear momentum when they bounce
off the walls.
Momentum is mass x velocity
Change of momentum is double
Collision is isothermal = perfectly elastic
The equal but opposite force at the wall creates the
pressure.
Fluid Pressure Measurement
 This force (pressure) depends on the fluid temperature
and density.
 A complete vacuum is absolute zero pressure.
 1 Pa = 1 N/m2
 101.32 kPa = standard atmospheric pressure
Fluid Pressure Measurement
Fluid Pressure Measurement
•Gage pressure can be positive or negative,
depending on whether the absolute pressure is,
respectively, greater than or less than the local
atmospheric pressure.
• When the absolute pressure is below
atmospheric pressure, some engineers use
vacuum pressure (Pvac), defined as the difference
between local atmospheric pressure (Patm) and
absolute pressure (Pabs).
• In equation form, Pgage =Pabs - Patm
• The top case is for Pabs < Patm, and the bottom
case is for Pabs > Patm.
o For the top case (Pabs < Patm), Pgage is negative
and Pvac is positive.
o For the bottom case (Pabs > Patm), Pgage is
positive and Pvac is generally not defined
since it would be negative.
Fluid Pressure Measurement
Fluid Pressure Measurement
Fluid Pressure Measurement
Measurement of Atmospheric Pressure
Measurement of Atmospheric Pressure
Measurement of Differential Pressure
Measurement of Differential
Pressure
Measurement of Differential Pressure
Manometry
Pressure Reference Instruments
Pressure Reference Instruments
Pressure Instruments
Pressure Transducers
 Usually hybrid transducers with the primary sensor
being an elastic element that deforms under pressure.
 A secondary transducer element converts the elastic
element deflection to an electrical or mechanical
output.
Pressure Instruments
Bourdon Tube Pressure Gauge
Aneroid
Potentiometer Pressure Transducer
Diaphragms Pressure Transducer
Diaphragms Pressure Transducer
Diaphragms Pressure Transducer
Diaphragms Pressure Transducer
Diaphragms Pressure Transducer
(using Strain Gauges)
Pressure Transducer Elements
Pressure Transducer Elements
Pressure Transducer Elements
(Capacitance Elements)
Pressure Transducer Elements
Pressure Transducer Elements
(Piezoelectric Crystal)
Pressure Transducer Elements
(Piezoelectric Crystal)
Pressure Transducer Elements
(Piezoelectric Crystal)
Pressure Measurements in
Moving Fluids
Pressure Measurements in Moving
Fluids
Pressure Measurements in Moving
Fluids
Pressure Measurements in Moving
Fluids
Static Pressure Measurement
Static Pressure Measurement (Prandtl Tube)
Static Pressure Measurement