Download Bourdon Gauge

Pacific school of Engineering
Sub: I.P.C
Topic: Pressure measurement
Mayani Chintak
Sudani Dhrutik
Bhikadiya Hardik
Kotadiya Hardik
Manavadariya Maulik
131120105027
131120105052
131120105005
131120105023
131120105026
Guided by
Piyush modi
Content
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Overview
Types of Measurement
U-tube Manometer
Bourdon Gauge
Diaphragm and Bellows Element
Strain Gauge
Piezoresistive Gauge
Quartz Gauge
Overview
Pressure (P ) expresses the magnitude of normal force (F-N) per unit area (A-m2)
applied on a surface
F
P 
A
or
F
P 
A
Units: Pa(= N/m2), psi(=lbf/in2), bar (=105 Pa=100 kPa), mbar (=100 Pa=1 hPa),
atm (=101.3 kPa), mmHg (or Torr), inHg, etc.
Pabs  Patm  Pgage
Where Pabs : Absolute pressure
Patm : Atmospheric pressure
(standard is: 101.3 kPa =14.696 psi=760 mmHg=29.92 inHg)
Pgage : Gage pressure
Types of Measurement
• Mechanical
– U-tube manometer, Bourdon tube, Diaphragm and Bellows
Mechanical pressure measurement devices are large and
cumbersome.
Not suited for automated control loops typical in
industry.
• Electrical
– Strain Gauge, Capacitive sensor, Potentiometric, Resonant
Wire, Piezoelectric, Magnetic, Optical
U-tube Manometer
• Measures difference in
pressure between two
points in a pipe.
• Typical in laboratories.
• Principles: Hydrostatic
Law
∆P=ρ g h
U-tube Manometer
Mercury Water Manometer
Air Water Manometer
Applications : air pressure, pipe pressure, etc.
Bourdon Gauge
• Flexible element used as
sensor.
• Pressure changes cause change
in element position.
• Element connected to pointer
to reference pressure.
Bourdon Gauge
• Principles: change in curvature of the tube is proportional to
difference of pressure inside from that outside the tube
• Applications: tire pressure, pressure at the top or along the
walls of tanks or vessels
Bourdon Gauge
-The Bourdon gauge consists of a bent tube with an elliptic cross section
closed at one end and connected at the other open end to the chamber in
which the pressure is to be measured.
-Pressure differences between the environment of the gauge and the interior
cause forces to act on the two walls of the tube so that it is bent by an
amount that depends on the pressure difference between the environment
and the interior.
-The bending is transformed by a lever to a pointer whose position can be
calibrated. The importance of this type of gauge is that it is very robust and
that it covers a range of pressure measurement from pressures higher than
atmospheric pressure down to rough vacuum (about10 mbar).
-The accuracy and reproducibility are relatively poor, so that it is not suitable
for precision measurements, and its usefulness for vacuum measurements is
limited.
Diaphragm and Bellows Element
• Similar concept to Bourdon
type.
• Widely used because they
require less space and can be
made from materials that resist
corrosion.
Diaphragm
If each element is sealed
with a known, fixed internal
pressure, flex will depend
on pressure change on
outside. Stacking amplifies
effect!
Strain Gauge
• Measures deflection of elastic diaphragm due to pressure
difference across diaphragm.
• Widely used in industry.
• Used for small pressure ranges.
• Measurements tend to drift.
Strain Gauge
Principles:
∆ P  ∆ Resistance ∆ Voltage
Applications: Sensors for internal combustion engines,
automotive, research etc.
Piezoresistive Gauge
• Measures the charge developed across quartz crystal due to
change in pressure.
• Charge decays rapidly making unsuitable for static pressure
measurements.
• Sensors are very rugged. Pressure can be applied
longitudinally or transversally.
• Used to measure dynamic pressure changes associated with
explosions and pulsations .
Piezoresistive Gauge
Digital Manometer
Principles: ∆Pressure = ∆Charge = ∆Resistance = ∆Voltage
Applications: Very accurate for small pressure differentials
e.g. Difference between indoor and outdoor pressure
Piezoresistive Gauge
-Similar to the diaphragm gauge the piezoresistive gauge consists of a small
evacuated capsule closed with a thin silicon diaphragm at the side exposed
to the space whose pressure is to be measured.
-On one side of this diaphragm are placed thin film piezoresists produced by
evaporation and which are connected to form a bridge circuit.
-By deformation of the silicon diaphragm the bridge is put out of balance
by an amount depending on the deformation. To avoid destruction of the
silicon diaphragm by corrosive gases there exist models in which a small
volume filled with special oil is placed between the silicon diaphragm and
the vacuum space.
-This volume is closed at the side of the vacuum space whose pressure is to be
measured by a thin stainless-steel diaphragm. The special oil serves as an
incompressible pressure transducer.
-Depending on the gauge construction the pressure reading covers a range of
0.1 to 200 mbar or 1 to 2000 mbar . The pressure reading is independent of
the kind of gas.
Quartz Gauge
Principles:
∆ Pressure  ∆ Charge  ∆ Voltage
Applications: measurements with high accuracy, good repeatability,
high resolution. e g. Quartz Clock