SENSORS
Week #4
Dr. Koray Gürkan
ELMU3925 – SENSORS
< Temperature Sensors >

Temperature = A measure of the average
energy of the particles in a material.

Thermal Energy = The total energy of all
the particles in a material.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Expansion and Contraction


Contract: Decrease in volume
Expand: Increase in volume

Temperature changes cause things to expand and
contract


Heated – usually causes expansion
Cooled – usually causes contraction

Usually more drastic in gases, then liquids then solids
Dr. Koray Gürkan
ELMU3925 – SENSORS

Heat Capacity: Amount of thermal
energy that warms or cools the object by
one degree Celsius.

Specific Heat Capacity: Amount of
thermal energy that warms or cools one
gram of a material by one degree Celsius.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Specific Heat Capacity
Dr. Koray Gürkan
ELMU3925 – SENSORS
P
V
T1
T2
= 2200 W
= 1 lt
= 25oC
= 100 oC
t = ??? seconds
Dr. Koray Gürkan
ELMU3925 – SENSORS
Heat Transfer

Heat always moves from a warmer place to a cooler place.

Hot objects in a cooler room will cool to room temperature.

Cold objects in a warmer room will heat up to room
temperature.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Question

If a cup of coffee and a ice cream were left on the
table in this room what would happen to them? Why?

The cup of coffee will cool until it reaches room
temperature. The ice cream will melt and then the
liquid will warm to room temperature.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Heat Transfer
Dr. Koray Gürkan
ELMU3925 – SENSORS
Conduction
https://www.youtube.com/watch?v=qW59Y9lJso8
When you heat a metal strip at one end, the heat
travels to the other end.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Conduction and Insulation

Thermal Conduction: The process of transferring
thermal energy through direct collisions between
particles.
 Examples

of good conductors???
Heat Insulators: Are very poor conductors
 Examples
Dr. Koray Gürkan
???
ELMU3925 – SENSORS
Metals are different
The outer e______
lectrons of metal atoms
drift, and are free to move.
When the metal is
heated, this ‘sea of
inetic
electrons’ gain k_____
energy and transfer it
throughout the metal.
Insulators, such as w___
ood and p____,
lastic do not
have this ‘sea of electrons’ which is why they
do not conduct heat as well as metals.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Why does metal feel colder than wood, if they
are both at the same temperature?
Metal is a conductor, wood is an insulator. Metal
conducts the heat away from your hands. Wood
does not conduct the heat away from your hands as
well as the metal, so the wood feels warmer than
the metal.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Convection
https://www.youtube.com/watch?v=0IUP665PQPU
Dr. Koray Gürkan
ELMU3925 – SENSORS
The third method of heat transfer
How does heat energy get
from the Sun to the Earth?
There are no particles
between the Sun and the
Earth so it CAN NOT
travel by conduction or
by convection.
?
Dr. Koray Gürkan
ELMU3925 – SENSORS
RADIATION
Radiant Energy

All forms of radiant energy share several characteristics:
- They behave like waves
- They can be absorbed and reflected by objects
- They travel across empty space at the same high speed of 300,000 km/s
Dr. Koray Gürkan
ELMU3925 – SENSORS
Dr. Koray Gürkan
ELMU3925 – SENSORS
Human Body Temperature


Your brain has its own temperature sensor.
It monitors your own internal temperature. If the temperature
outside changes, the sensor signals your brain to release chemicals
that will help your body adjust to normal temperature (37°C)
Temperature Sensors

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Dr. Koray Gürkan
Thermocouples
Resistance Temperature Detectors (RTDs)
Thermistors
Infrared Sensors
Semiconductors
ELMU3925 – SENSORS

Thermocouples
Dr. Koray Gürkan
ELMU3925 – SENSORS
Thermocouple
Thomas Johann Seebeck
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ELMU3925 – SENSORS
Thermocouple
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ELMU3925 – SENSORS
Thermocouple Junction Materials
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ELMU3925 – SENSORS
Thermocouple
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ELMU3925 – SENSORS
Thermocouple
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ELMU3925 – SENSORS
Thermocouple
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ELMU3925 – SENSORS
Thermocouple
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ELMU3925 – SENSORS
Thermocouples

Two wires of different metal alloys.

Converts thermal energy into electrical energy.

Requires a temperature difference between
measuring junction and reference junction.

Easy to use and obtain.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Thermocouple Applications

Plastic injection molding machinery

Food processing equipment

Deicing

Semiconductor processing

Heat treating

Medical equipment

Industrial heat treating

Packaging equipment
Dr. Koray Gürkan
ELMU3925 – SENSORS
Thermocouples
Advantages
Simple, Rugged
 High temperature
operation
 Low cost
 No resistance lead wire
problems
 Point temperature sensing
 Fastest response to
temperature changes

Dr. Koray Gürkan
Disadvantages

Least stable, least
repeatable

Low sensitivity to small
temperature changes

Extension wire must be of
the same thermocouple type

Wire may pick up radiated
electrical noise if not
shielded

Lowest accuracy
ELMU3925 – SENSORS
Thermocouples
Dr. Koray Gürkan
ELMU3925 – SENSORS


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
Dr. Koray Gürkan
Thermocouples
Resistance Temperature Detectors (RTDs)
Thermistors
Infrared Sensors
Semiconductors
ELMU3925 – SENSORS
Resistance Temperature Detectors (RTDs)
Dr. Koray Gürkan
ELMU3925 – SENSORS
Resistance Temperature Detectors
(RTDs)

Wire wound and thin film
devices.

Nearly linear over a wide range
of temperatures.

Can be made small enough to
have response times of a
fraction of a second.

Require an electrical current to
produce a voltage drop across
the sensor
Dr. Koray Gürkan
ELMU3925 – SENSORS
RTD Applications

Air conditioning and
refrigeration servicing

Furnace servicing

Foodservice processing

Medical research

Textile production
Dr. Koray Gürkan
ELMU3925 – SENSORS
Dr. Koray Gürkan
ELMU3925 – SENSORS
Dr. Koray Gürkan
ELMU3925 – SENSORS
Dr. Koray Gürkan
ELMU3925 – SENSORS
Dr. Koray Gürkan
ELMU3925 – SENSORS
RTDs
Advantages
Disadvantages
Most stable over time
 Most accurate

High cost

Slowest response time
Most repeatable
temperature
measurement
 Very resistant to
contamination/
 corrosion of the RTD
element

Low sensitivity to small
temperature changes

Sensitive to vibration
(strains the platinum
element wire)

Decalibration if used beyond
sensor’s temperature ratings

Somewhat fragile


Dr. Koray Gürkan
ELMU3925 – SENSORS

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

Dr. Koray Gürkan
Thermocouples
Resistance Temperature Detectors (RTDs)
Thermistors
Infrared Sensors
Semiconductors
ELMU3925 – SENSORS
Thermistors




A semiconductor used as a temperature sensor.
Mixture of metal oxides pressed into a bead, wafer or other shape.
Beads can be very small, less than 1 mm in some cases.
The resistance decreases as temperature increases, negative temperature
coefficient (NTC) thermistor. (PTC ?)
Dr. Koray Gürkan
ELMU3925 – SENSORS
Thermistors

Most are seen in medical
equipment markets.

Thermistors are also used
are for engine coolant, oil,
and air temperature
measurement in the
transportation industry.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Thermistors
Dr. Koray Gürkan
ELMU3925 – SENSORS
 NTC
45
Dr. Koray Gürkan
ELMU3925 – SENSORS
Thermistors
Advantages
High sensitivity to
small temperature
changes
 Temperature
measurements
become more stable
with use
 Copper or nickel
extension wires can be
used

Dr. Koray Gürkan
Disadvantages





Limited temperature
range
Fragile
Some initial accuracy
“drift”
Decalibration if used
beyond the sensor’s
temperature ratings
Lack of standards for
replacement
ELMU3925 – SENSORS
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


Dr. Koray Gürkan
Thermocouples
Resistance Temperature Detectors (RTDs)
Thermistors
Infrared Sensors
Semiconductors
ELMU3925 – SENSORS
Dr. Koray Gürkan
ELMU3925 – SENSORS
Infrared Radiation
Dr. Koray Gürkan
ELMU3925 – SENSORS
Planck's law
F ( ) 
1

2 hc
5
e
hc
kT
2
1
Magnitude of radiation at particular
wavelength (λ) and particular temperature
(T).
h is Planck’s constant and c speed of light.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Infrared Radiation
Dr. Koray Gürkan
ELMU3925 – SENSORS
Infrared Radiation



Heat can be “seen” at a distance.
Some of this energy is emitted as photons.
A photon of energy E and frequency f satisfies:
E=hf


where h is Planck’s constant = 6.63 x 10-34 J sec
Thermal photons have frequency ~ 1013 Hz and wavelength ~ 30 m
This is in the far infrared range. Sensors that respond to those
wavelengths can “see” warm objects without other illumination.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Infrared Sensors

An infrared sensor intercepts a portion of the infrared energy radiated by an object.

Many types Optical Pyrometers, Radiation Pyrometers, Total Radiation Pyrometers, Automatic
Infrared Thermometers, Ear Thermometers, Fiber optic Thermometers, Two-Color Pyrometers,
Infra-Snakes, and many more.
Digital Plug & Play Infrared Thermometer
MLX90614
Factory calibrated in wide temperature range:
-40 to 125°C for sensor temperature
-70 to 380°C for object temperature
Dr. Koray Gürkan
ELMU3925 – SENSORS
Thermopile IR Sensor
Dr. Koray Gürkan
ELMU3925 – SENSORS
Thermal imagers
Dr. Koray Gürkan

Far infrared CCD cameras exist for 10 m and above, but are much
more sophisticated (and expensive) than near-infrared CCDs.

Generally many > $1000
ELMU3925 – SENSORS
Bolometer
Dr. Koray Gürkan
ELMU3925 – SENSORS
Dr. Koray Gürkan
ELMU3925 – SENSORS
Emissivity
Dr. Koray Gürkan
ELMU3925 – SENSORS
PIR Sensors

PIR (Pyroelectric InfraRed) sensors can detect IR heat radiation (7-20 m typical).

They are simple, cheap and common. The basis of security system “motion detectors”.

Most PIR sensors contain
two or four sensors with
different viewing regions.

They detect a change
in the difference between
the signals and give a
binary output.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Infrared Sensors
Advantages





No contact with the
product required
Response times as fast or
faster than thermocouples
No corrosion or oxidation
to affect sensor accuracy
Good stability over time
High repeatability
Disadvantages






Dr. Koray Gürkan
High initial cost
More complex - support
electronics required
Emissivity variations affect
temperature measurement
accuracy
Field of view and spot size
may restrict sensor
application
Measuring accuracy affected
by dust, smoke, background
radiation, etc.
ELMU3925 – SENSORS
Semiconductors

Are small and result from the fact that semiconductor diodes have voltagecurrent characteristics that are temperature sensitive.

Temperature measurement ranges that are small compared to thermocouples
and RTDs, but can be quite accurate and inexpensive.
Dr. Koray Gürkan
ELMU3925 – SENSORS
Classic Bandgap Temperature Sensor
Dr. Koray Gürkan
ELMU3925 – SENSORS
Semiconductor Applications

Hard Disk Drives

Personal Computers

Electronic Test Equipment

Office Equipment

Domestic Appliances

Process Control

Cellular Phones
Dr. Koray Gürkan
ELMU3925 – SENSORS
Texas Instruments TMP 100/101
Dr. Koray Gürkan
ELMU3925 – SENSORS
Dr. Koray Gürkan
ELMU3925 – SENSORS
MAX30205
Human Body Temperature Sensor
Clinical Grade Temperature Sensor Offers ±0.1°C (max)
Accuracy for Thermometer Applications
Dr. Koray Gürkan
ELMU3925 – SENSORS
MAX30205
Human Body Temperature Sensor
Clinical Grade Temperature Sensor Offers ±0.1°C (max)
Accuracy for Thermometer Applications
Dr. Koray Gürkan
ELMU3925 – SENSORS