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CHAPTER 5 : PRESSURE MEASUREMENT, Introduction, Moderate Pressure…
CHAPTER 5 : PRESSURE MEASUREMENT
P=F/A
Fluid can be gas or liquid
Unit: Pascal (Pa) or N/m²
Manometer
Simplest device to measure static pressure
h = (p1-p2) /pg
Characteristics
Non-corrosive and not have any chemical reaction
Low viscosity
Negligible surface tension and capillary effects
Bourdon Tube
Measure pressure
When pressure applied the elastic elements will get deformed
The elastic elements
Diaphagram
Bellows
Corrugated diaphragm
Capsule
Bourdon tube
Helical tube
The technique based on the electrical resistance change of a
manganin (alloy of Cu, Ni, Mn) or gold chrome wire, with hydrostatic pressure to accommodate a bulk compression effect
The coil is enclosed in a flexible bellows, filled with kerosene
(medium of transmitting pressure to the coil)
Changes in
resistance of the wire between is measured by usual
methods like Wheatstone bridge
Unit : Torr or Micron
1 Torr = 1mmHg
1 micron = 10¯³ Torr
Vacuum gauges
Thermal Conductivity Gauge or Pirani Gauge
Consists of a metal sensor wire (usually gold plated tungsten or platinum) suspended in a tube which is connected to the system whose vacuum is to be measured. The connection is usually made either by a ground glass joint or a flanged metal connector, sealed with an o-ring. The sensor wire is connected to an electrical circuit from which, after calibration, a pressure reading may be taken.
Ionisation Gauge
In the hot cathode type, a column of gas is introduced into which, a potential difference V is applied with free electron in the space. This causes the electron with a charge e to acquire a kinetic energy Ve
McLeod Gauge
Operate by taking in a sample volume of gas from a vacuum chamber, then compressing it by tilting and infilling with mercury
Knudsen Gauge
Works with the interaction of particles with a surface. Particles that interact with a hotter or colder surface will exert a force on that surface
Introduction
Moderate Pressure Measurement
High Pressure Measurement
Low Pressure Measurement
LVDT measurement range is 100 to 10^8 PA
