Download Manometer

Lecture 11
Pressure Measurements
Techniques to measure pressure.
Pressure Measurement
• Pressure
Pressure = Force/Area
Units of force per unit area
• Pressure measurements.
– All pressure measurements are relative
measurements.
– The measurement of a pressure at a point is relative
to, or referred to, a reference pressure.
Pressure References
• Absolute Pressure:
– Measured relative to a zero pressure or a
perfect vacuum.
• Gauge Pressure:
– Measured relative to the local ambient
pressure.
• Differential Pressure:
– Measured pressure between two point.
Barometer
• Aneroid from Greek aneros – “not wet”
Mercury Barometer
• Measurement of Atmospheric Pressure
Manometers
• Manometers are one of the oldest
pressure measuring devices.
How could you make a U-tube
manometer more sensitive?
• Change Manometer fluid.
• Incline the manometer.
• Combine inclined and straight sections.
Inclined Manometer
Pressure Transducers
• What is a pressure transducer?
– A pressure transducer is a device that
converts a pressure signal to an electric
signal.
• What type of devices can be used to
create a pressure transducer?
• Strain gage devices
• Capacitance devices
• Piezoelectric devices
Pressure Transducer
Strain gage device
Strain gage is attached to a flexible
membrane. When the membrane is
deflected the resistance in the strain
gage changes.
Pressure Transducer
Capacitance device
The capacitance between two plates changes
with the distance between the plates.
Pressure Transducer
Piezoelectric device
Piezoelectric device take advantage of the
electrical properties of crystals such as
quartz. These crystals generate an
electrical charge when they are strained.
Pressure Sensitive Paint
Pressure Probes to Measure
Velocity
• Pitot Static Probe
Measuring Velocity Components
• Five hole Pressure Probe
How would you calibrate this
probe?
Pressure Models
• Airfoils, wings and complete airplane
models equipped with pressure ports can
be used to determine model loads and
load distribution.
• Pressure models provide more detail on
how the loads are generated than a force
balance.
• Disadvantage is pressure measurement of
model forces is more time consuming.
How to you create a pressure
model?
• Suppose you have designed a new airfoil
section and you want to determine its
aerodynamic performance and its
pressure distribution, how would make
such a model?