Pressure & Temperature Measurement Electrical methodNon electrical method of temperature measurement Optical PyrometerThermoelectric methodPressure Thermometer Ionization gaugePirani Gauges

1. Pressure & Temperature
Measurement
Karmaveer Bhaurao Patil Poly, Satara
Prof. Waghmode D R

2. Pressure Measurement
• Pressure Measurement Pressure is defined as the force acting
per unit area exerted by a fluid on surface.
• Its unit is N/m2 or Pa. 1 mm of Hg (Mercury) = 133 Pa =
133 N/m2 , 1 bar = 105N/m2.
• Atmospheric Pressure (Patm) Atmospheric pressure is the
pressure on the surface of earth due to the atmospheric gases.
• It is normally expressed at sea level. 1atm = 101.36 kPa = 760
mm of Hg Gauge Pressure (Pgauge)
• Gauge pressure is the pressure measured with respect to
atmospheric pressure. It is the difference between absolute
pressureand atmospheric pressure. Pgauge =Pabs -Patm

3. • (A)Low Pressure Gauges.
• (a) McLeod Gauge.
• (b) Thermal conductivity gauge.
• (i) Thermocouple vacuum gauge.
• (ii) Pirani gauge.
• (c) lonization gauge.
• (B) High Pressure Gauges.
• (a) Elastic pressure gauges.
• (i) Diaphragm. (ii) Bellows. (iii) Bourdon tube.
• (b) Electrical pressure gauges
• (i) Resistance type
• (ii) Photo electric type
• (iii) Piezoelectric type
• (iv) Variable capacitor type

4. McLeod gauge
• McLeod gauge use a glass tubing made of tough glass
and mercury is used to trap the known volume of gas.
• The gauge is connected to the unknown gas whose
pressure is to be measured.
• The plunger moves up, lowers the mercury level to the
cut off positions, entering the gas at unknown pressure
through the tube.
• Now plunger is moved down to rise the mercury above
the cut-off point.
• Further pushing of plunger compresses the gas in the
measuring capillary and mercury in the reference
capillary reaches to zero reference line

5. • Pressure in the measuring capillary is higher
than the measured pressure in the reference
capillary. This differences in pressure causes
the difference in mercury level in two tubes

6. McLeod- Gauge

7. Thermal conductivity gauge
• Ability of material to conduct the heat by
conduction.
• That thermal conductivity changes as change
in pressure

8. Thermal conductivity gauge

9. Pirani Gauges
• Pirani gauges consist of platinum enclosed in
chamber. Wire form an arm of wheatstone
bridge.
• The temperature of wire for a given magnitude
of current, depends on rate of heat dissipation
which is depend on conductivity of
surrounding medium and hence pressure.
• So with change in pressure of the medium
there for temperature also change and hence
the resistance of wire chances.
• Which can be measured by using wheatstone
bridge

11. Ionization gauge
• Ionization means process of producing free
electron and a positively charged ions by
knocking off an electron.

13. High pressure Gauge
• Elastic pressure gauge
-diaphragm
-bellows
- Bourdon tube type
• Electrical pressure gauges
• Photoelectric pressure gauge
• Piezoelectric pressure gauge

14. Diaphragm pressure gauges

15. Bellows pressure gauges

16. Bourdon tube pressure gauges

17. Photoelectric Transducer
• When the pressure to be measured is applied
through port to the pressure sensing member,
it changes the position of window. As the
light source and phototube are separated by
a window it changes the amount of light
falling on phototube, causing change in
current.

18. Photoelectric Transducer

19. Strain gauge pressure transducer
• Strain gauge is a resistance type gauge whose
electrical resistance changes when it is
stretched or compressed

20. Strain gauge pressure transducer

21. Piezoelectric Pressure Transducer
• Piezoelectric crystal placed between a solid
base and the pressure sensing element like
diaphragm. under the action of pressure, the
diaphragm deflects producing deformation in
crystal, there by produces an emf which is the
function of applied pressure.

22. Piezoelectric Pressure Transducer

23. Temperature
Measurement

24. Non electrical method of temperature
measurement
1 Expansion type thermometer
a) Expansion of solid
Bimetallic thermometer.
b) Expansion of liquid
liquid in glass thermometer.
c) Expansion of gas

25. Bimetallic Thermometer
• Two different material having different coefficient
of thermal expansion rigidly joined together one
on other to form a bimetallic strip.
• When bimetallic strip is fixed at one end and
heated from free end its bend in the direction of
material having low thermal coefficient of
expansion.
• The bending movement of free end is connected
to the pointer which moves over calibrated scale.

26. Bimetallic Thermometer

27. Pressure Thermometer
• The bulb is connected by means of a capillary
tube to a pressure measuring device, like a
bourdon tube pressure gauge. An increase in
temperature causes the liquid to expand, thereby
increasing the pressure on the gauge.
• The bulb is partially filled so that when the bulb
senses the temp. vapour will be formed in the
remaining space in the bulb, and passed through
a capillary tube to the indicator with a bourdon
tube.

28. Pressure Thermometer

29. Liquid in glass thermometer

30. Electrical method
• Thermocouple
• Resistance thermometer
• termister

31. RTD(Resistance temperature
detector)
• RTD measure the temperature by measuring
the electrical resistance of the pure platinum
wire.
• RTD work on positive temperature coefficient
of resistance I e as temp increases resistance
offered by thermometer also increases.
•

32. RTD(Resistance temperature
detector)

33. Thermister
• 1 Negative temperature coefficient Thermister
In this type of thermister as temperature
increases its resistance decreases. It made of
semi- conducting material like as sintering
powder mixture of metallic oxide such as
manganes, nickel, cobalt, copper, iron.
• Made in different size and shape

34. Thermister

35. Thermoelectric method
• These type devise work on principle of
thermoelectric effect in which e.m.f generated
across the two junction of dissimilar metal
wire and magnitude of e.m.f measured
directly proportional to change in temperature

36. • Seebeck effect- if two
dissimilar wire are
joined together at each
end and form a
complete electric circuit
then current flows in
the circuit when the
two junction are kept at
different temperature.
• Emf is in the circuit is a
function of temp
difference.

37. • Peltier Effect:
• It is reverse of Seebeck
effect. According to this,
when an electric
current is passed
through thermo-couple
, one junction become
hot while other become
cold.

38. Thermocouple

39. • The law of intermediate
temperatures states that
the emf generated in a
thermocouple with
junctions
at temperatures T1 and T3
is equal to the sum of emfs
generated by similar
thermocouples, one with
its junctions
at temperatures T1 and T2,
and other with its junctions
at temperatures T2 and T3

40. • Law of Intermediate Metal-
The Introduction of a third
metal into the thermocouple
circuit will have no effect on
the emf generated as long as
the junctions of third metal
with thermocouple metals are
at the same temperature

41. A pyrometer is a type of remote-sensing thermometer
used to measure the temperature of a surface

43. Optical Pyrometer

44. • The working principle of optical pyrometer state that the brightness of
light of a given color emitted by a hot source, gives an indication of
temperature.
• Working:
• It consists of a tube, one end of this tube has objective lens and other end
has a sighting eye piece to observe the filament.
• The filament is viewed through filter and eye piece. The lens side of tube
is projected towards the hot body whose temperature is to be measured.
• An image of radiating source is produced by a lens and made to coincide
with the filament of an electric lamp.
• The current through the lamp filament is made variable so that lamp
intensity can be adjusted. The current through filament is adjusted until
the filament and the image are of equal brightness.
• During the operation of optical pyrometer following conditions occurs.
1. When the temperature of the filament is higher than that required for
equal brightness then the filament is too bright as shown in the figure.
2. When the temperature of filament is lower, the filament becomes too
dark as shown in fig.
3. When the brightness of image produced by the source and brightness
produced by the filament are equal, the outline of the filament
disappear.

45. Radiation Pyrometer