PRACTICAL THERMOMETERS

TOPIC 10 : TEMPERATURE

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1Sunday, February 20, 2011

SO MANY TYPES OF THERMOMETERS !

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2Sunday, February 20, 2011

WHAT ARE THE COMMON SIMILARITIES BETWEEN THEM?

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3Sunday, February 20, 2011

FEATURES OF A THERMOMETERGood thermometers have the following features:

Safe to Use

Easy to read scale

Able to measure a wide range of temperature

Responsive to temperature

changes

Sensitive to small temperature

changes

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4Sunday, February 20, 2011

WHAT CHARACTERISTICS CAN BE USED TO DESCRIBE

THERMOMETERS ?

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5Sunday, February 20, 2011

CHARACTERISTICS OF THERMOMETER

COMMON CHARACTERISTICS

SENSITIVITY

RANGE

LINEARITY

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6Sunday, February 20, 2011

RANGE

The lowest reading to the highest reading that can be measured.Definition

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7Sunday, February 20, 2011

RANGEWhat is the range of this thermometers?

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8Sunday, February 20, 2011

RANGEWhat is the range of this thermometers?

Thermometer A Thermometer B

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9Sunday, February 20, 2011

SENSITIVITY

How large the change in reading is when there is a small change in temperature.

Definition

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10Sunday, February 20, 2011

LINEARITY

Uniform increase/decrease of the thermometric properties used with equal increase/decrease in temperature

Definition

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11Sunday, February 20, 2011

LIQUID-IN-GLASS THERMOMETERS

Laboratory Thermometer Clinical Thermometer

LENGTH

Physical property used to measure temperature:

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12Sunday, February 20, 2011

LABORATORY THERMOMETER

Laboratory Thermometer

To measure temperatures or changes in

temperatures with high degrees of accuracy.

Function

Normally used in

laboratories.

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13Sunday, February 20, 2011

LABORATORY THERMOMETERIts Structure & Function

Thin wall glass bulb

Allow conduction of heat quickly through

the glass

Function

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14Sunday, February 20, 2011

LABORATORY THERMOMETERIts Structure & Function

Small bulbStore small amount of

liquid.Small amount of liquid is more responsive to

heat

Function

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15Sunday, February 20, 2011

LABORATORY THERMOMETERIts Structure & Function

Fine & Uniform Capillary bore

Allows noticeable movement of liquid column for small

change in temperature

FunctionAllows

even expansion of the liquid.

Function

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16Sunday, February 20, 2011

LABORATORY THERMOMETERIts Structure & Function

Thick long tube walls

Acts as a magnifying glass for easy reading

of scales.

Function

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17Sunday, February 20, 2011

LABORATORY THERMOMETERIts Structure & Function

Small-sized thermometer

Portable and cheap to produce.

Function

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18Sunday, February 20, 2011

CLINICAL THERMOMETERS

Clinical Thermometer

To measure body temperature.

Function

Normally used at home

or in hospitals / clinics. Pre

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19Sunday, February 20, 2011

CLINICAL THERMOMETERIts Structure & Function

Thin wall glass bulb Allow rapid conduction

of heat through the glass

Function

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20Sunday, February 20, 2011

CLINICAL THERMOMETERIts Structure & Function

Very fine capillary bore

Allows for greater measurement

sensitivity

Function

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21Sunday, February 20, 2011

CLINICAL THERMOMETERIts Structure & Function

Limited short scale range

Allows for greater measurement

accuracy

Function

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22Sunday, February 20, 2011

CLINICAL THERMOMETERIts Structure & Function

Narrow constriction above the bulb

Prevents the liquid from entering the bulb

too quickly.

FunctionProvides

a more steady temperature reading

Function

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23Sunday, February 20, 2011

CLINICAL THERMOMETERIts Structure & Function

Pear-shaped cross-section of the stem.

Acts as a magnifying glass in one direction

for easy reading of temperature scales.

Function

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24Sunday, February 20, 2011

LABORATORY VS CLINICAL

LIST OUT THREE

DIFFERENCES BETWEEN

THEM

Thermometers

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25Sunday, February 20, 2011

IMPROVING THERMOMETER DESIGN

More Responsive to temperature

changes

for Liquid-in-glass thermometers

Decrease the thickness of the

bulb’s wall.

Thinner glass bulb will allow faster and better conduction of heat to the mercury / alcohol

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26Sunday, February 20, 2011

IMPROVING THERMOMETER DESIGN

More Sensitive to small temperature

changes

for Liquid-in-glass thermometers

Decrease the size of the bore.

Smaller bore size will be able to produce larger liquid column change for very small change in temperature.

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27Sunday, February 20, 2011

IMPROVING THERMOMETER DESIGN

Measure larger range of

temperature.

for Liquid-in-glass thermometers

Increase the length of the bore and thermometer.

Longer bore will allow further expansion of the mercury / alcohol column with temperature.

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28Sunday, February 20, 2011

THERMOCOUPLE

Thermocouple Thermometers

VOLTAGE / EMF

Physical property used to measure temperature:

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29Sunday, February 20, 2011

THERMOCOUPLE

To measure wide range of temperatures, rapidly

changing temperatures and temperatures of small

objects.

Function

Normally used in

industries.

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30Sunday, February 20, 2011

THERMOCOUPLEIts Structure

A si

mpl

e th

erm

ocou

ple

ther

mom

eter

Voltmeter

Cold Junction

Hot Junction

Two types of wires

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31Sunday, February 20, 2011

Cold Junction

Hot Junction

THERMOCOUPLECalibrating the temperature scale on a thermocouple

ICE POINTSTEAM POINT

0 degrees Celsius

100 degrees Celsius

Voltmeterreading This value gives us the Calibration Temperature

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32Sunday, February 20, 2011

THERMOCOUPLEUsing a simple thermocouple

Voltmeterreading

Cold Junction

Hot Junction

Keep at ICE POINT

Put in Unknown

Temperature

This value gives us the Temperature Difference

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33Sunday, February 20, 2011

THERMOCOUPLE READINGS

Ice pointSteam point

Unknown temp

-

-X= 100

Unknown temperature

in0C V V

Ice pointVV

Use with the Centrigrade Equation to determine the temperature

Thermocouple thermometer measures the temperature difference between the two junctions.

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34Sunday, February 20, 2011

Cold Junction

Hot Junction

THERMOCOUPLETo determine the temperature in Centrigrade / Celsius:

ICE POINT

STEAM POINT

Voltmeterreading This value gives us the Calibration Temperature

Ice point

Steam point

V V-

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35Sunday, February 20, 2011

THERMOCOUPLE

Voltmeterreading

Cold Junction

Hot Junction

ICE POINT

Unknown Temperature

This value gives us the Temperature Difference

To determine the temperature in Centrigrade / Celsius:

Unknown temp

- Ice pointVV

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36Sunday, February 20, 2011

THERMOCOUPLE READINGS

Ice pointSteam point

Unknown temp

-

-X= 100

Unknown temperature

in0C V V

Ice pointVV

Thermocouple thermometer measures the temperature difference between the two junctions.

Use with the Centrigrade Equation to determine the temperature

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37Sunday, February 20, 2011

THERMOCOUPLEAdvantages of Using Thermocouple Thermometer

Can measure temperatures over a very large range

Can measure temperatures at a

point

Very responsive to rapidly changing temperatures

Can be connected to electrical equipment for

checking rapid temperature changes

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38Sunday, February 20, 2011

IMPROVING THERMOMETER DESIGN

More Sensitive to temperature

changes

for Thermocouple thermometers

Connect several thermocouple

together in series

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Several Thermocouples connected in series is known as a Thermopile.

39Sunday, February 20, 2011