This presentation summarizes different temperature measurement devices. It discusses common thermometers like liquid-in-glass, bimetallic, and pressure spring thermometers. It also covers thermocouples, which measure temperature based on the thermoelectric effect between two dissimilar metals. Resistance thermometers are described as measuring temperature through changes in electrical resistance. Finally, pyrometers are summarized as non-contact devices that measure the infrared radiation emitted from an object to determine its temperature.

1. Presentation Report
Name : Javiya Smit A.
Enrollment No. : 180470105019
Subject : Instrumentation &
Process control
Department : Chemical
Presentation on
Temperature Measurement

2. Temperature Measurement
• On the whole, the temperature is the most important variable
in industry processing, primarily because its is fundamental
condition characteristic of the thermal state of body.
• The thermometer is, the most widely used instrument
processing of all kinds.
• it is simple to use and economical and provides reliable
performance under variety of application conditions.
• Thermometers are employed for the measurement of
temperature.

3. Classification of Temperature
Measurement Devices
1) Thermal expansion devices (thermometers):
 Liquid in glass thermometer
 Bimetallic thermometer
 Pressure spring thermometer
2) Thermocouples
3) Resistance thermometers
 Includes metallic resistance sensors (rtds)

4. Constant Volume Gas Thermometer

5. Constant Volume Gas Thermometer
•The physical change exploited is the variation of pressure of a
fixed volume gas as its temperature changes.
•The volume of the gas is kept constant by raising or lowering the
reservoir B to keep the mercury level at A constant.
•The pressure is indicated by the height difference between
reservoir B and column A.
•The thermometer is calibrated by using a ice water bath and a
steam water bath.
•The pressures of the mercury under each situation are recorded.
•The volume is kept constant by adjusting A.

6. Mercury In Glass Thermometer
• The mercury-in –glass thermometer, widely
used in both laboratory and industry, is one of
the simplest temperature measuring devices.
• It utilizes the volumetric expansion of mercury
with temperature as a means of indicating the
temperature.
• As shown in figure , the typical industrial
thermometer has a bulb formed by a glass
envelope, which contains mercury , enclosed in
a metal well.

7. Mercury In Glass Thermometer
• As heat is transferred through the well and metal stem and into
the mercury, the mercury expands, pushing the column of
mercury higher in the capillary above.
 Its construction is as follow;
• It is contained in a metal case with the bulb inserted into a
metal thermal well.
• A metal scale is mounted behind the upper end of
thermometer, and a glass covers the scale.
• This provides the complete protection for the thermometer
itself, making rugged and compact instrument.
• The steam is generally protected and insulated by packing.

8. Mercury In Glass Thermometer
• Thermal is well provided for purpose of preventing
breakage and providing a sealing means at the point of
installation.
• It is generally of brass or steal although cast iron,
Monel, stainless steal, and aluminium are sometimes
used.
• The temperature range in which the Industrial mercury-
in-glass thermometer is used is -38 to 950 degree F.

9. Bimetallic Thermometer
• The Bimetallic thermometer is commonly
used whenever the industries mercury-in-
glass thermometer is employed.
• Its construction provides a rugged yet
accurate and simple device for the
indication of temperature.
• It is composed of two strips of metal
welded together, each strip made from
metal having different coefficient of
thermal expansion.

10. Bimetallic Thermometer
• For a bimetal in the form of straight cantilever beam,
temperature changes cause to free end to deflect, and this
deflection can be related quantitatively to the temperature
change.
• Deflection with the temperature is nearly linear, depending
mainly on coefficients of linear thermal expansion.
• Invar is universally employed as low expansion metal, it is an
iron-nickel alloy containing about 36% nickel, its temp.
coefficient of expansion is about 1/20 that of ordinary metals
• As high expansion metal, brass is used at lower temp and
nickel at higher temperature.

11. Pressure Spring Thermometer
• The liquid expansion thermometer utilizes the
cubical expansion of liquid, generally mercury
to indicate the temperature.
• The gas expansion thermometer operates at
substantially constant volume , the pressure of
the gas being proportional for temperature.
• Vapor-actuated thermometer is operated by
vapor pressure of liquid.
• A metal bulb contains the thermometer fluid, a
liquid, a gas, or a liquid-vapor, and is inserted at
the point at which temp is to be measured.

12. Pressure Spring Thermometer
• The bulb comes to the temp equilibrium with its surroundings,
thereby developing a given pressure of fluid.
• A metal capillary is connected to the bulb and transmits the
pressure to the bulb to the receiving element at the instrument.
• The receiving element is a form of bourdon tube and is used to
convert pressure of the fluid in the thermometer bulb into a
motion.
• This motion is multiplied by a linkage to operate a pen arm
over a moving chart for recording purposes.
• The thermal system, consisting of bulb, capillary and receiving
element is a hermitically scaled unit.

13. • The construction thermometer bulb and thermal well is
shown in figure.
• The bulb is composed of cylindrical piece of metal tubing,
closed at one end and with the capillary and extension neck
inserted at the other end.
• The size of bulb varies considerably, depending on type of
filling medium, temp span of instrument, and length of
capillary tubing with which it is used.

14. Thermocouple as Measuring Devices
• The thermocouple pyrometer has the widest
useful range and application of any
temperature-measuring device.
• It provides an accurate and reliable
indication of temperature for many kinds
of industrial applications.
• They can be interchanged since they are
supplied to a standard calibration.

15. Thermoelectricity
• A thermocouple is composed of two dissimilar wires joined
together so as to produce thermal emf.
• A simple thermoelectric circuit composed of two wires of
different metals, A and B. assume that lefthand junction of the
wire is the point of measurement.
• Then the left-hand junction is called measuring junction,
right-hand junction is called reference junction, and its
frequently maintained at either 32 degree F or 68 degree F.

16. • The Thomson Effect is a relation between emf generated in
a single homogeneous wire and temp difference between the
ends of wire.
• The thomson emf is propotional to temp and the temp
difference in wire and differs for different metals.
• The Peltier Effect relates the absorption and evolution of
heat at the junction of a thermocouple to the current flow in
the circuit.
• It is proportional to current alone and is different from joule
heating effect , which is proportional to the square of the
current times the resistance.
• Thus thermocouple employs both Peltier Effect and
Thomson Effect.

17. Laws Of Thermoelectric Circuits
LAW OF HOMOGENEOUS CIRCUIT:
• An electric current cannot be
sustained in a circuit of a single
homogeneous metal, however
varying in section, by application of
heat alone.
LAW OF INTERMEDIATE METALS:
• The algebraic sum of thermal emf’s
in a circuit composed of any number
of dissimilar metals is zero, if all the
circuit is at a uniform temperature.

18. LAW OF INTERMEDIATE TEMPERATURE
• The thermal emf developed by any thermocouple of
homogeneous metals with its junction at any two
temperatures T1 and T3, respectively is the algebraic
sum of the emf of thermocouple with its junctions at
temperature T1 and T2 respectively, and the emf of the
same thermocouple with its junction s at temperatures
T2 and T3 , respectively.

19. Resistance Thermometer Circuits
• Measurement of temperature with a resistance
thermometer reduces to a measurement of
electrical resistance.
• Its techniques of resistance measurement are
well advanced, and high accuracy and
precision are not difficult to obtain.
• The wheatstone bridge with various
modification required for use with a resistance-
thermometer bulb is the most common method
of measurement.
• It is basic system for measurement of
resistance. A battery applies potential across
two of the junction points ,and galvanometer
connects the resistances.

20. Pyrometer
• All matter that has a temperature(T) greater than absolute
zero emits electromagnetic radiation(photon particles) due to
the internal mechanical movement of molecules.
• Radiation thermometers or pyrometers are measurement
instruments which determine the temperature of an object
based on the infrared radiation emitted from that object.
 Types Of Pyrometer:
I. Radiation pyrometer
II. Optical pyrometer

21. Radiation Pyrometer
 Principle:
• Temperature measurement is based on the measurement of
radiation either directly by a sensor or by comparing with the
radiation of a body of known temperature.
• The radiation pyrometer is non-contact type of temperature
measurement.
• The wavelength region having high intensity is between 0.1 to
10 micrometer.
• In this region, 0.1 to 0.4 micrometer is known as ultraviolet
region.
• 0.4 to 0.7 micrometer is known as the visible region. 0.7
micrometer onwards is the infrared region.

22. • With the increasing temperature, the radiation intensity is
stronger towards shorter wavelengths.
• The temperature measurement by radiation pyrometer is limited
within 0.5 to 8 micrometer wave length region.
• Radiation pyrometer consist of optical component to collect the
radiation energy emitted by object , a radiation detector that
converts the radiant energy in to an electrical signal and an
indicator to read the measurement.

23. Optical Pyrometer
• This pyrometer is also known as disappearing filament
pyrometer.
 Main principle :
• In this type of pyrometer, the tungsten filament of an
electric bulb is used as radiator.
• The intensity of radiation of filament is compared with the
intensity of the radiation of the hot surface.
• When both the intensity match, the filament of bulb is
disappears against the background.

25. • The intensity of filament can be controlled by current
flowing through it.
• The maximum temperature of the filament is 2800 to 3000
°C at the rated voltage.
• The minimum visible radiation is at 600°C . Hence we can
measure the temperature in between 600°C.

26. Thank You