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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
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