The document discusses various types of temperature sensors and smoke detectors. It describes optical smoke detectors that use light scattering or blocking to detect smoke, ionization detectors that detect changes in air ionization from smoke, and resistance thermometers that measure temperature changes by measuring changes in electrical resistance of metals like platinum. Thermistors are also covered, which are semiconductors with a negative temperature coefficient of resistance used for temperature sensing. Thermocouples are discussed as devices that generate voltage from the Seebeck effect of dissimilar metals joined at different temperatures.

1. Transducer
Presented by
Amit Kumer Podder
Assistant Professor,
Department of Electrical and Electronic Engineering,
Khulna University of Engineering & Technology.
Course No: TE 2221

2. Smoke Detector/Sensor
• A smoke detector is a device that senses smoke, typically as an indicator of
fire. Commercial and residential security devices issue a signal to a fire alarm
control panel as part of a fire alarm system, while household detectors,
known as smoke alarms, generally issue a local audible or visual alarm from
the detector itself.
• TYPES:
Optical
Ionization
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3. Optical
• Uses incandescent bulb or Light-emitting diode, a lens, and a
photoelectric receiver (typically a photodiode)
• Two types
Scattered light
Blocked light
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4. Scattered Light Method
• Under normal operation, the light passes the photodetector
Smoke scatters the light
Photodetector catches scattered light
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5. Blocked Light Method
• A tight beam of light shines from source to detector
Smoke blocks path, triggering alarm
This type can span large rooms
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6. Pros
Less Prone to false alarms
Less sensitive to steam and cooking fumes
Better at detecting smoke from smoldering fires
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7. Cons
Slower to detect smoke than ionization method
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8. Ionization
A radioactive source ionizes the air between two electrodes.
An ionization smoke detector uses a radioisotope such as
americium-241 to produce ionization in air; a difference due to
smoke is detected and an alarm is generated. Ionization detectors are
more sensitive to the flaming stage of fires than optical detectors,
while optical detectors are more sensitive to fires in the early
smoldering stage.
Changes in the current, due to particulate matter,
trigger an alarm
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10. Pros
Detects particles too small to be visible
Cheaper than optical detector
Better at detecting smoke from hot fires
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11. Cons
Most prone to false alarms
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12. Resistance Thermometer
Resistance-temperature detectors(RTD), or resistance thermometers,
employ a sensitive element of extremely pure platinum, copper, or
nickel that provides definite resistance value at each temperature
within its range.
Principle of working: The resistance of a conductor changes when its
temperature is changed. This property is utilized for measurement of
temperature. The variation of resistance R with temperature T (ºK)
can be represented by the following relationship for most of the
metals as:
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13. Resistance Thermometer
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14. Resistance Thermometer
• The sensing element of a resistance thermometer is selected according to the
intended application. Platinum wire is used for most laboratory work and for
industrial measurements of high accuracy . Nickel wire and copper wire are less
expensive and easier to manufacture than platinum wire elements, and they are
often used in low-range industrial applications.
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15. Resistance Thermometer
• The Table below summarizes the characteristics of the three most commonly
used resistance materials.
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16. Resistance Thermometer
• Platinum RTD is the most widely used.
Advantages:
• Wide operating temperature range.
• Stability at high temperature.
• Linearity.
Disadvantages:
• Low sensitivity.
• Expensive.
• Easily affected by contact resistance
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17. Thermistor
• Thermistor is a contraction of a term “thermal resistor” .
Thermistor are temperature dependent resistors. They are made of
semiconductor material which have negative temperature coefficient of resistivity i.e.
their resistance decreases with increase of temperature.
Thermistor are widely used in application which involve measurement in the
range of 0-60º Thermistor are composed of sintered mixture of metallic oxides
such as manganese, nickle, cobalt, copper, iron and uranium
The thermistor provide a large change in resistance for small change in
temperature. In some cases the resistance of themistor at room temperature may
decreases as much as 6% for each 1ºC rise in temperature.
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18. Thermistor
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19. Thermistor
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20. Thermistor
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21. Applications of Thermistor
• Major applications of thermistors are measurement and control of temperature.
Other applications of thermistors:
• Measurement of power at high frequencies.
• Measurement of thermal conductivity.
• Measurement of level, flow and pressure of liquids.
• Measurement of composition of gases.
• Vacuum measurement
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22. Thermocouples
• See beck Effect
When a pair of dissimilar metals are joined at one end, and there is a temperature
difference between the joined ends and the open ends, thermal emf is generated,
which can be measured in the open ends.
• This forms the basis of thermocouples.
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23. Thermocouples
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24. Thermocouples
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