Seminar report on Temperature Measuring Devices

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SEMINAR REPORT
ON
TEMPERATURE MEASURING INSTRUMENT
GUIDE – Dr. SUSHANTA TRIPATHY
SUBMITTED BY –
NAME – AMBRISH RAI
ROLL NO – 1102027
SECTION – M1
BRANCH – MECHANICAL
SEMESTER - 8TH

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First, I would like to thank SCHOOL OF MECHANICAL ENGINEERING,
for putting SEMINAR & TRAINING in academic curricula. I would also like
to thank Dr. SUSHANTA TRIPATHY , for being my support
for Seminar & Training.
Apart from this, I would also like to thank GOOGLE & WIKIPEDIA,
because I got adequate information for the preparation of my report from
them..
And last, but not the least I would like to thank my friends who helped me
on this seminar.
Submitted by:
AMBRISH RAI
(1102027)

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SL
NO.
TITLE Page No.
1 Introduction to TEMPERATURE 4
2 SCALE 5-6
3 Types Of Temperature measuring Devices 7
4 LIQUID IN THERMOMETER 8-9
5 Bimetallic Thermometer 10-11
6 Resistance Temperature Detector (RTD) 12-14
7 Pyrometer 15-19

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Introduction:-
Temperature measurement in today’s industrial environment encompasses a wide variety of
needs and applications. To meet this wide array of needs the process controls industry has
developedalarge numberof sensorsanddevicestohandle thisdemand.Inthisexperiment you
will have an opportunity to understand the concepts and uses of many of the common
transducers,andactuallyrunan experimentusingaselectionof these devices.Temperature is a
verycritical and widelymeasuredvariable formostmechanical engineers.Manyprocessesmust
have eitheramonitoredorcontrolledtemperature. This can range from the simple monitoring
of the water temperature of an engine or load device, or as complex as the temperature of a
weld in a laser welding application. More difficult measurements such as the temperature of
smoke stackgas from a powergeneratingstationorblast furnace or the exhaust gas of a rocket
may be needtobe monitored.Muchmore commonare the temperaturesof fluids in processes
or process support applications, or the temperature of solid objects such as metal plates,
bearings and shafts in a piece of machinery.
The history of temperature measurement-
There are a wide varietyof temperature measurementprobesinuse today depending on what
you are trying to measure, how accurately you need to measure it, if you need to use it for
control or just man monitoring, or if you can even touch what you are trying to monitor.
Temperature measurementcanbe classifiedintoafew general categories: a) Thermometers b)
Probes c) Non-contact Thermometers are the oldest of the group. The need to measure and
quantify the temperature of something started around 150 A.D. when Galen determined the
‘complexion’ of someone based on four observable quantities. The actual science of
‘thermometry’ did not evolve until the growth of the sciences in the 1500’s The first actual
thermometerwasanair-thermoscopedescribed in Natural Magic (1558, 1589). This device was
the fore runner of the current class of glass thermometers. Up to 1841 there were 18 different
temperature scalesinuse.Aninstrumentmaker,DanielGabriel Fahrenheit learned to calibrate
thermometers from Ole Romer, a Danish astronomer. Between 1708 and 1724 Fahrenheit
beganproducingthermometersusingRomer’sscale andthenmodifiedthattowhatwe know to
day as the Fahrenheit scale. Fahrenheit greatly improved the thermometer by changing the
reservoirtoa cylinderandreplacedthe spiritsused in the early devices with mercury. This was
done because ithada nearlylinearrate of thermal expansion.Hiscalibrationtechniques were a
trade secret,but itwas known that he used a certain mixture of the melting point of a mixture
of sea salt, ice and water and the armpit temperature of a healthy man as calibration points.
Whenthe scale wasadoptedbyGreat Britainthe temperature of 212 wasdefinedasthe boiling
point of water. This point as well as the melting point of plain ice were used as two known
calibrationpoints.About1740 AndersCelsiusproposedthe centigrade scale. It is not clear who
inventedthe scale,butitdivided the range of the melting point of ice (100) to the steam point

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of water(0) into100 parts, hence ‘centigrade’.Linnaeusinverted the scale so that 0 was the ice
point and 100 was the steam point. In 1948 the name of the centigrade scale was changed to
Celsius.Aboutthe time thatFahrenheitwasexperimentingwithhisliquid filled devices, Jaspeh
L. Gay-Lussac was working with gas filled tubes. He concluded that at a constant pressure, the
volume of the gas would expand at a particular rate for each degree of temperature rise, that
being1/267 perdegree.In1874 VictorRegnaultobtained betterexperimental results, showing
this number to be 1/273 and concluded that the pressure would approach zero at 1/273.15
degrees C. This lead to the definition of zero pressure at -273.15 degrees C, or what we now
know as the absolute scale.
Scale
 Temperature is a measure of the thermal energy in the body.
Normally measured in degrees [°]using one of the following
scales.
1. Fahrenheit.[°F]
2. Celsius or centigrade. [°C]
3. Kelvin .[°K]

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TYPES OF INSTRUMENT :
• Thermometer - 1.Liquid – in – Glass
Thermometer & /
2.Bimetallic Thermometer
3. Pressure Thermometer -1.Liquid
Pressure & 2.Vapor Pressure
• Thermocouples
• Thermistor
• Resistance temperature detector (RTD)
• Pyrometer
• Langmuir probes (for electron temperature of
a plasma)
• Infrared
Coti
1.Liquid – in – Glass Thermometer
CONSTRUCTION
1.Bulb: The reservoir for containing most of the thermometric liquid
(mercury).
2.Stem: The glass tube having a capillary bore along which the liquid
moves with changes in temperature.

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3. Scale: A narrow-temperature-range scale for reading a reference
• The volume of mercury changes slightly with temperature; the
small change in volume drives the narrow mercury column a
relatively long way up the tube.
• The space above the mercury may be filled with nitrogen or it
may be at less than atmospheric pressure, a partial vacuum.
 Advantages
1) Simplicity in use & low cost.
2) Portable device.
3) Checking physical damage is easy.
4) Power source not require.
 Disadvantages
1) Can not used for automatic recording.
2) Time lag in measurement.
3) Range is limited to about 300 °C .
2.Bimetallic Thermometer
 In an industry, there is always a need to measure and monitor
temperature of a particular spot, field or locality.
 The industrial names given to such temperature sensors are
Temperature Indicators (TI) or Temperature Gauges (TG).

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 All these temperature gauges belong to the class of
instruments that are known as bimetallic sensors.
 Two basic principles of operation is to be followed in case of
a bimetallic sensor.
1) A metal tends to undergo a volumetric dimensional change
(expansion/contraction), according to the change in temperature.
2) Different metals have different co-efficient of temperatures. The
rate of volumetric change depends on this co-efficient of
temperature.

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• The device consists of a bimetallic strip of two different metals .
• They are bonded together to form a spiral or a twisted helix.
• Both these metals are joined together at one end by either
welding or riveting.
• It is bonded so strong that there will not be any relative motion
between the two.
The image of a bimetallic strip is shown below
Construction
 A change in temperature causes the free end of the strip to expand or
contract due to the different coefficients of expansion of the two metals.
 This movement is linear to the change in temperature and the deflection of
the free end can be read out by attaching a pointer to it.

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 This reading will indicate the value of temperature. Bimetallic strips are
available in different forms like helix type, cantilever, spiral, and also flat
type.
 Advantages
1) Power source not required
2) Robust, easy to use and cheap.
3) Can be used to 500 °C.
 Disadvantages
1) Not very accurate.
2) Limited to applications where manual reading is acceptable.
3) Not suitable for very low temperatures because the expansion of
metals tend to be too similar, so the device becomes a rather
insensitive thermometer

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Pressure Thermometer
1. Liquid Pressure Thermometers.
2. Vapour Pressure Thermometers
Resistance Temperature Detector (RTD)
RTD can also be called a resistance thermometer as the temperature
measurement will be a measure of the output resistance.
The main principle of operation of an RTD is that when the temperature
of an object increases or decreases, the resistance also increases or
decreases proportionally.
ie. positive temperature coefficient
RTD Types
RTD types are broadly classified according to the different sensing
elements used.
Platinum, Nickel and Copper are the most commonly used sensing
elements.

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Resistance Temperature Detector (RTD)
Resistance Temperature Detector-(RTD)-2 Wire
Copper lead wires are satisfactory for all the arrangements.
For a given RTD, all the lead-wires should be of the same gauge and the same length, and
should be run in the same conduit
• Advantages
1. Very high accuracy
2. Excellent stability and reproducibility
3. Interchangeability
4. Ability to be matched to close tolerances for temperature difference
measurements.

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5. Ability to measure narrow spans
6. Suitability for remote measurement
• Disadvantages
1. Susceptibility to mechanical damage
2. Need for lead wire resistance compensation
3. Sometimes expensive
4. Susceptibility to self-heating error
5. Susceptibility to signal noise
6. Unsuitability for bare use in electrically conducting substance
7. Generally not repairable
8. Need for power supply
Pyrometer
• A pyrometer is a device that is used for the temperature measurement of
an object.
• The device actually tracks and measures the amount of heat that is radiated
from an object.
• The thermal heat radiates from the object to the optical system present
inside the pyrometer.
The optical system makes the thermal radiation into a better focus and
passes it to the detector
• In an optical pyrometer, a brightness comparison is made to measure the
temperature.

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• The device compares the brightness produced by the radiation of the
object whose temperature is to be measured,
• For an object, its light intensity always depends on the temperature of the
object.
• After adjusting the temperature, the current passing through it is measured
using a multimeter, as its value will be proportional to the temperature of
the source when calibrated.
• The working of an optical pyrometer is shown in the figure below.
 As shown in the figure above, an optical pyrometer has the following
components.

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1. An eye piece at the left side and an optical lens on the right.
2. A reference lamp, which is powered with the help of a battery.
3. A rheostat to change the current and hence the brightness intensity.
4. So as to increase the temperature range which is to be measured, an
absorption screen is fitted between the optical lens and the reference bulb.
WORKING
1.The radiation from the source is emitted and the optical objective lens
captures it.
2.The lens helps in focusing the thermal radiation on to the referencebulb.
3.The observer watches the process through the eye pieceand corrects it in
such a manner that the reference lamp filament has a sharp focus and the
filament is super-imposed on the temperature source image.
4.The observer starts changing the rheostat values and the current in the
reference lamp changes.
5.This in turn, changes its intensity This change in current can be observed
in three different ways.

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The filament is dark. That is, cooler
than the temperature source.
Filament is bright. That is, hotter than
the temperature source.
Filament disappears. Thus, there is
equal brightness between the filament
and temperature source
At this time, the current that flows in the reference lamp is measured, as its
value is a measure of the temperature of the radiated light in the temperature
source, when calibrated
• Advantages
1. Provides a very high accuracy with +/-5º Celsius.
2. The biggest advantage of this device is that, there is no direct contact
between the pyrometer and the object whose temperature is to be found out.
• Disadvantages
1. As the measurement is based on the light intensity, the device can be used
only in applications with a minimum temperature of 700º Celsius.
2. The device is not useful for obtaining continuous values of temperatures at
small intervals.

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Applications
3. Used to measure temperatures of liquid metals or highly heated materials.
4. Can be used to measure furnace temperatures.
The radiation pyrometer has an optical system, including a
lens, a mirror and an adjustable eye piece. The heat energy
emitted from the hot body is passed on to the optical lens,
which collects it and is focused on to the detector with the
help of the mirror and eye piece arrangement. The detector
may either be a thermistor or photomultiplier tubes.
Though the latter is known for faster detection of fast
moving objects, the former may be used for small scale
applications. Thus, the heat energy is converted to its
corresponding electrical signal by the detector and is sent to
the output temperature display device.
Internet Sites:
(i)www.google.com
(ii)www.wikipedia.org

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(iii)www.nptel.ac.in

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