1

SEMINAR REPORT

ON

TEMPERATURE MEASURING INSTRUMENT

GUIDE – Dr. SUSHANTA TRIPATHY

SUBMITTED BY –

NAME – AMBRISH RAI

ROLL NO – 1102027

SECTION – M1

BRANCH – MECHANICAL

SEMESTER - 8TH

2

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)

3

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

4

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

developed a large number of sensors and devices to handle this demand. In this experiment you

will have an opportunity to understand the concepts and uses of many of the common

transducers, and actually run an experiment using a selection of these devices. Temperature is a

very critical and widely measured variable for most mechanical engineers. Many processes must

have either a monitored or controlled temperature. 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 stack gas from a power generating station or blast furnace or the exhaust gas of a rocket

may be need to be monitored. Much more common are the temperatures of 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 variety of temperature measurement probes in use 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 try ing to monitor.

Temperature measurement can be classified into a few 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

thermometer was an air-thermoscope described 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 scales in use. An instrument maker, Daniel Gabriel Fahrenheit learned to calibrate

thermometers from Ole Romer, a Danish astronomer. Between 1708 and 1724 Fahrenheit

began producing thermometers using Romer’s scale and then modified that to what we know to

day as the Fahrenheit scale. Fahrenheit greatly improved the thermometer by changing the

reservoir to a cylinder and replaced the spirits used in the early devices with mercury. This was

done because it had a nearly linear rate of thermal expansion. His calibration techniques were a

trade secret, but it was known that he used a certain mixture of the melting poi nt of a mixture

of sea salt, ice and water and the armpit temperature of a healthy man as calibration points.

When the scale was adopted by Great Britain the temperature of 212 was defined as the boiling

point of water. This point as well as the melting point of plain ice were used as two known

calibration points. About 1740 Anders Celsius proposed the centigrade scale. It is not clear who

invented the scale, but it divided the range of the melting point of ice (100) to the steam point

5

of water (0) into 100 parts, hence ‘centigrade’. Linnaeus inverted 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. About the time that Fahrenheit was experimenting with his liquid 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

being 1/267 per degree. In 1874 Victor Regnault obtained better experimental 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]

6

7

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.

8

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).

9

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.

10

• 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.

11

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

12

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.

13

14

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.

15

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.

16

• 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.

17

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.

18

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.

19

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

20

(iii)www.nptel.ac.in

21