pressure measuring devices

1. MINI PROJECT
GROUP MEMBERS:
• Aqeel Ur Rehman
• Naseem khan
• Aqib Ahmad
• Asmat Ullah
• Ubaid Ullah

2. TOPICS
• Pressure measuring devices
• Piston gauge
• Manometers
• Bourdon pressure gauge
• McLeod gauge

3. PRESSURE MEASURING DEVICES
• Instruments used to measure pressure are called pressure gauges or
vacuum gauges
• The oldest type is the liquid column (a vertical tube filled with mercury)
manometer invented by Evangelista Torricelli in 1643.
• The U-Tube was invented by Christian Huygens in 1661.

4. McLeod Gauge
Principle :
A known volume gas is compressed to a smaller volume whose final value provides an
indication of the applied pressure
• A McLeod gauge isolates a sample of gas and compresses it
• McLeod gauge reading is dependent on the composition of the gas
Useful range:
• Useful range is from 10−4Torr (roughly 10−2 Pa) to vacuums as high as 10−6 Torr
• McLeod gauge can measure lower pressure directly

5. McLeod Gauge
COMPONENTS AND
WORKING:
Applied pressure P1
Mercury level is raised by piston
Mercury level reaches zero
reference point
Here we find pressure

6. MEASUREMENT OF PRESSURE
• P1 = ah2/(V1-ah)
Where, h = height of the compressed gas in the measuring capillary tube
P1 = Applied pressure of the gas unknown.
P2 = Pressure of gas at final condition= P1+h
• Since ah is very small when compared to V1, it can be neglected.
Therefore, P1 = ah2/V1
APPLICATION
The McLeod Gauge is used to measure vacuum pressure

7. BOURDON PRESSURE GAUGE
• Bourdon patented his gauge in France in 1849
• Cheap, reliable and accurate
• Principle: flattened tube tends to straighten or regain its circular form in
cross section when pressurized

8. COMPONENTS OF BOURDON GAUGE
• Glass plate
• Face plate
• Screws
• Housing/casing
• Pivot and pivot pin
• Link
• Sector gear
• Pinion
• Needle

9. WORKING
• Increased pressure………….. Flattened tube tends to straightened and
needle rotates clockwise
• Decreased pressure……….... Tube tends to contract and needle rotates counter
clockwise
APPLICATIONS
• Cars
• Industries

10. WORKING
CONTD

11. PISTON GAUGE
• Piston-type gauges counterbalance the
pressure of a fluid with a spring (for example
tire-pressure gauges of comparatively
low accuracy) or a solid weight

12. DEADWEIGHT
TESTER
• Pressure measuring device
and also used for calibration
• Principle: pressure of the
fluid is counter balanced by
the weights and friction drag
COMPONENTS AND
WORKING:

13. CALCULATING PRESSURE
• PA = Mg + F
Hence : P = (Mg + F ) / A
where, P = pressure
M = Mass; Kg
g = Acceleration due to gravity ; m/s²
F = Friction drag; N
A = Equivalent area of piston – cylinder combination; m²
Thus the pressure P which is caused due to the weights placed on the platform is
calculated.

14. APPLICATIONS
• It is used to calibrate all kinds of pressure gauges
such as industrial pressure gauges, engine
indicators and piezoelectric transducers

15. MANOMETERS
DIFFERENTIAL
MANOMETER:
 It is used to measure
pressure difference
between two pipelines or
containers.
 Components:
1) U shaped tube
2) Liquid (mercury or
water)
 Working
 Calculation

16. • PA+ ρAg*(x+h) = PB+ ρBg*y+ ρmg*h
• PA-PB = (ρBg*h+ ρmg*h)- ρAg*(x+h)
• In this way we can find pressure difference

17. MANOMETERS
CONTD
INCLINED
MANOMETER:
 It is slant manometer
 It is used to measure very
small pressure difference
 Components :
 Working:
 Calculation:

18. Pa+ ρ a*g*(Rm+x) =
Pb+ ρb*Rm*g+ ρa*g*x

19. AQIB AHMAD
CLASS NO 14

20. Aneroid Gauges
• Aneroid means “without fluids” and the term originally distinguished
these gauges can be used to measure the pressure of a liquid as well as
gas.
• Aneroid gauges are based on a metallic pressure-sensing element that
flexes elastically under the effect of a pressure difference across the
element.
• Aneroid gauges are often called mechanical gauges in modern languages.
• These are not dependent on the type o gas being measured , unlike thermal
and ionization gauges.

21. • Ionization gauges for measuring low pressure only .
• Thermal gauges are used by the phenomenon that
DENSITY INCREASES PRESSURE INCREASES
HEAT PRODUCED HEAT MEASURED BY WIRE FILAMENT

22. Bellow Pressure Gauge
WORKING:
• Bellows are tubular membranes which are present inside the bellow
pressure gauge.
• Here the pressure to be measured is applied outside the bellows.
• It contains an elastic element that is spring.
• Here the movements of the bellows can be converted into linear
displacement.
• The displacement can be converted in terms of pressure.

23. • Used to measure the flow pressure
of a peaceful river etc.
Application
• It is adaptable for absolute and
differential pressures

24. Spinning Rotor Gauge
• The spinning rotor gauges works by measuring the amount of a rotating ball is
slowed by the viscosity of the gas being measured.
• Here the ball is made of steel and is magnetically levitated inside the steel tube
closed at one end and exposed to the gas to be measured at the other.
• The range of this instrument is 0.000001 Pa to 100 Pa.
• It is accurate and stable enough to be used as a secondary standard.
• Also this instrument requires some special skills and knowledge to use it
correctly.

25. • Spinning rotor
gauge

27. Application of spinning gauge
• High vacuum gauge calibration and metrology.
• Gas kinetics measurements.
• Thermal and chemical research

28. Magnetic coupling
• These gauges use the attraction of two magnets to translate differential
pressure into motion of a dial pointer.
• As differential pressure increases , a magnet attached to either a piston or
rubber diaphragm moves .
• A rotary magnet that is attached to a pointer then moves in union ,to create
different pressure ranges, the spring rate can be increased or decreased.