Pressure Measurement

1. Pressure
Measurement

2.  INTRODUCTION
 UNITS OF PRESSURE
 CLASSIFICATION OF PRESSURE MEASUREMENT

3. INTRODUCTION
Pressure means force per unit area, exerted by a
fluid on the surface of the container.
P=F/A
F - FORCE (in Newton)
A - AREA (in meter²)
Pressure is of two types-
STATIC PRESSURE
DYNAMIC PRESSURE
WHERE,
F

4. Pressure Measurement scale
4#
•
•
•
•
Absolute Pressure
Measured above total vacuum or zero absolute. Zero absolute represents total lack of
pressure.
• Atmospheric Pressure
The pressure exerted by the earth’s atmosphere. Atmospheric pressure at sea level is 14.696
psia. The value of atmospheric pressure decreases with increasing altitude.
Barometric Pressure
Same as atmospheric pressure.
Gauge Pressure
The pressure above atmospheric pressure. Represents positive difference between measured
pressure and existing atmospheric pressure. Can be converted to absolute by adding actual
atmospheric pressure value.
Differential Pressure
The difference in magnitude between some pressure value and some reference
pressure. In a sense, absolute pressure could be considered as a differential pressure
with total vacuum or zero absolute as the reference. Likewise, gauge pressure (defined
above) could be considered as Differential Pressure with atmospheric pressure as the
reference.

5. Pressure is of two types-
1 STATIC PRESSURE
2 DYNAMIC PRESSURE
STATIC PRESSURE- when the force in a system
under pressure is constant or static (i.e. unvarying),
the pressure is said to be static pressure.
DYNAMIC PRESSURE- If the force is varying, on
the other hand, the pressure is said to be dynamic
pressure.

6. 1atm = 14.7Psi at sealevel
= 101.3Kilo Pascal
= 760mm of Hg
= 10.3m of water
= 1013mili bar
1Pascal = 1N/m2
1Bar = 100Pascal

7. MECHANICAL ELECTROMECHANICAL
STATIC DYNAMIC(Force Summing Devices)
MANOMETER
U-TUBE
WELLTYPE
INCLINED
DIAPHRAM BELLOWS BOURDON-TUBE
CLASSIFICATION OF PRESSURE MEASUREMENT
FLAT CORRUGATED CAPSULE
C-TYPE HELICAL
TYPE
SPIRAL
TYPE

8. ELECTROMECHANICAL
POTENTIO
METER
PHOTOELECTRIC CAPACITIVE
TYPE
PIEZOELECTRIC
TYPE
INDUCTIVE

10. This manometer consist of U-
shaped tube in this manometric fluid
is filled.
Water and mercury are used as a
manometric fluid.
Advantage of using these fluid is
that mass density of these fluid can
be obtained easily and they do not
stick to the tube.

11. Since, P = ρgh
h = (P₁ -
P₂)/ρg P₁ - P₂
= ρgh
Where, ρ - mass density of fluid
g - gravity
P₁ - unknown pressure
P₂ - atmospheric
pressure

13. The well type manometer is widely
used because of inconvenience; the
reading of only a single leg is required in
it.
It consist of a very large-diameter vessel
(well) connected on one side to a very
small-sized tube.
Thus the zero level moves very little
when pressure is applied.

15. The force summing devices are those which
converts the applied pressure into
displacements by primary transducers while
generated displacements may be measured by
secondary transducers.
The commonly used force summing devices
are-
1 DIAPHRAGM
2 BALLOWS
3 BOURDON TUBE

16. Diaphragm are widely used for pressure
(gauge pressure), particularly in very low
ranges. They can detect a pressure differential
even in the range of 0 to 4mm.
The diaphragm can be in the form of Flat,
Corrugated and Capsules the choice depends
on the strength and amount of deflection
required.

17. A bellows gauge contains an
elastic element that is a
convoluted unit that expands
and contracts axially with
change in pressure.
The pressure to be measured
can be applied to the outside or
inside of the bellows however,
in practice, most bellows
measuring devices have the
pressure applied to the outside
of the bellows.

18. An elastic transducer , that is
bourdon tube which is fixed and
open at one end to receive the
pressure which is to be measured.
The other end of the bourdon tube
is free and closed.
The bourdon tube is in a bent
form to look like a circular arc.
All the various form of bourdon
tube have the common feature
that they are constructed the tube
of non circular cross-section