Temperature Measuring Seonsors

Precision Engineering & Metrology
Temperature Measuring Sensors
Zaeemnaqvi@hotmail.com

Presented By
 Zaeem Sajjad Naqvi UET-2K14-ME-076
Swedish College of Engineering &
Technology Wah Cantt

Temperature
 scalar quantity
 Degree of hotness or coldness
 Molecular K.E. = Temperature

How is heat transferred?

Sensors
 A sensor is a device that converts real world data (Analog) into
data that a computer can understand using ADC (Analog to
Digital converter)
 A sensor is a device that detects and responds to some type of
input from the physical environment. The specific input could
be light, heat, motion, moisture, pressure, or any one of a
great number of other environmental phenomena. The output
is generally a signal that is converted to human-readable
display at the sensor location or transmitted electronically over
a network for reading or further processing.

Temperature Sensors
 Temperature Sensors are devices that can sense the
difference amount of heat between application space
and reference.
 They are used to measure temperature and change
of heat transfer of a medium.

Temperature Sensors
Technology Name
A-Mechanical • Thermometer
• Therm
B-Electrical • Thermistor
• Themocouple
• Resistance thermometer(RTD’s)
C-Wirless • Pyrometer

A-Thermometer
 Thermometer is temperature
measuring device
 It is filled with a liquid such as
heat can cause expansion or
evoporation on it. So that,
liquid can pressurized. The
pressure is related to the
temperature and it may be
indicated on a simple gauge.Zaeemnaqvi@hotmail.com

A-Thermometer
 Advanteges ; Low cost , Simple construction
 Disadvantages;No remote measurement
 Range
 According to British Standards, correctly calibrated,
used and maintained liquid-in-glass thermometers
can achieve a measurement uncertainty of ±0.01
°C in the range 0 to 100 °C

A-Therm(bi metallic)
 Therm is also known as bi-metallic
 A bimetallic strip is used to convert a
temperature change into mechanical
displacement. The strip consists of two
strips of different metals which expand
at different rates as they are heated,
usually steel and copper, or in some
cases steel and brass
 Bimetal strips are used in
miniature circuit breakers to protect
circuits from excess current.Zaeemnaqvi@hotmail.com

B-Thermocouple
 A thermocouple is a comparison of at least two
metals joined together to form two junctions one
is connected to the body of known
temperature(hot body) and other junction is
connected with the body of unknown
temperature(cold body).thermocouple measure
the unknown temperature of body with respect to
known temperature body.
 A variety of thermocouples are available, suitable
for different measuring applications
 They are usually selected based on the
temperature range and sensitivity needed

B-Thermocouple
Working principle

B-Thermocouple
ADVANTAGES AND
DISADVANTAGES
 They are simple, strong, need no
batteries, measure over very wide
temperature ranges.
 The main limitation is accuracy; System
errors of less than 1°C can be difficult to
achieve

B-Thermocouple
APPLICATIONS
 Thermocouples are most suitable
for measuring over a large
temperature range, up to 1800 °C
 These are widely used in the steel
industry, heating appliances,
manufacturing of electrical
equipment's like switch gears etc.

B-Thermistor
 A thermistor is a type of resistor with resistance
varying according to its temperature.
 The resistance is measured by passing a small,
measured direct current through it and measuring
the voltage drop produced.
 There are basically two broad types
1. NTC-Negative Temperature Coefficient: used
mostly in temperature sensing
2. PTC-Positive Temperature Coefficient: used
mostly in electric current control.

B-Thermistor
 TYPES OF THERMISTORS
 NEGATIVE TEMPERATURE
COEFFICIENT:
A NTC thermistor is one in which the
zero-power resistance decreases with an
increase in temperature.
 POSITIVE TEMPERATURE
COEFFICIENT:
A PTC thermistor is one in which the
zero-power resistance increases with an
increase in temperature

B-Thermistor
ADVANTAGESAND DISADVANTAGES
• Thermistors, since they can be very small, are used inside many
other devices as temperature sensing and correction devices
• Thermistors typically work over a relatively small temperature
range, compared to other temperature sensors, and can be very
accurate and precise within that range

APPLICATIONS
• PTC thermistors can be used as current-limiting devices for circuit
protection, as replacements for fuses.
• PTC thermistors can be used as heating elements in small temperature-
controlled ovens.
• NTC thermistors are used as resistance thermometers in low-temperature
measurements of the order of 10 K.
• NTC thermistors are regularly used in automotive applications.

B-Resistance Thermometer
 Resistance thermometers, also
called resistance temperature
detectors (RTDs), are sensors used to
measure temperature.
 RTD’s are the resistance of a conductor usually
increase as the temperature increase.
 If the properties of that conductor are known,
the temperature can be calculated from the
measured resistance.
 The most common RTD’s are PT100, PT 1000
and Ni100
 The different RTD’s analyse 0°C with different
resistive values. For example, PT 100 is 100Ω at
0°C.
 The temperature can be found by using The
Callender Van-Dusen equations.

 RTD’s has different wiring and
connection type for sensitivity of
application.
 Lead and reference pins are
depending on measurement
sensitivity.

Common Resistance Materials for
RTDs:
Platinum (most popular and accurate)
Nickel
Copper
Tungsten (rare)
CONSTRUCTION OF RTD

• CONSTRUCTION OF RTD
• RTD elements consist of a length of fine coiled wire wrapped around a
ceramic or glass core
• The element is usually quite fragile, so it is often placed inside a
sheathed probe to protect it
• The RTD element is made from a pure material whose resistance at
various temperatures has been documented.
• The material has a predictable change in resistance as the temperature
changes; it is this predictable change that is used to determine
temperature

C-Pyrometer
 A pyrometer is a type of thermometer used to measure
high temperatures. It is used for measuring temperature
without any physical contact. Its is used for measuring
body temperature by measuring its electromagnetic
radiation
Principle
 Its principle depends upon the relationship between temperature of a
hot body and electromagnetic radiation emitted by the body. When a
body is heated it emits thermal energy known as heat radiation. It is a
technique for determining a body temperature by measuring its
electromagnetic radiation

C-Pyrometer
Types
 Optical pyrometer
 Radiation pyrometer
Radiation pyrometer
Optical pyrometer

C-Pyrometer
 Optical pyrometer
 The Optical Pyrometer is a highly-developed and well
accepted noncontact temperature measurement
device.
 It is widely employed for accurate measurement of
the temperature of furnaces, molten and other
heated materials.
 It is primarily used in the range of 1000 to 5000 ⁰F.

C-Pyrometer

C-Pyrometer
 Working
 Optical Pyrometers work on the basic principle of using the human eye to
match the brightness of the hot object to the brightness of a calibrated lamp
filament inside the instrument.
 The radiation from the source is emitted and the optical objective lens
captures it. The lens helps in focusing the thermal radiation on to the
reference bulb.
 The observer watches the process through the eye piece and 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.
 The observer starts changing the rheostat values and the current in the
reference lamp changes. This in turn, changes its intensity.

C-Pyrometer
 This change in current can be observed in three
different ways :

C-Pyrometer
 Advantages
 Simple assembling of the
device enables easy use of it.
 Provides a very high accuracy
with +/-5 degree Celsius
 There is no need of any direct
body contact between the
optical pyrometer and the
object. Thus, it can be used
in a wide variety of
applications.
Disadvantage
• As the measurement is
based on the light intensity,
the device can be used only
in applications with a
minimum temperature of
700 degree Celsius.
• The device is not useful for
obtaining continuous values
of temperatures at small
intervals

C-Pyrometer
Applications
 Used to measure
temperatures of liquid
metals or highly
heated materials.
 Can be used to
measure furnace
temperatures.
Technician measuring the temperature of molten silicon at
2650°F with a disappearing filament pyrometerZaeemnaqvi@hotmail.com

Temperature Measuring Sensors
Technology Names Range cost
A-Mechanical • Thermometer
• therm
0-100°C
-17.7-537.7°C
Low
Low
B-Electrical • Thermistor
• Thermocouple
• Resistance
thermometer(RTD’s)
-20 to 120°C
-200 to 600°C
Low
High
C-Wireless • Pyrometer Upto 1400°C High

Temperature Measuring Seonsors

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