Transcript Transducer

Transducers
Saneeju M Salu
Transducer
Any device that converts energy in one form
to energy in another from
Physical
Quantity
Transducer
Electrical
Quantity
(Current/ Voltage)
Device which converts one physical quantity
or condition to another
Physical quantity – heat , intensity of light, flow rate, liquid level,
humidity etc
Classification of transducers
1.
2.
3.
4.
Based on principle of transduction
Active & passive
Analog & digital
Based on Electrical Principle
Based on principle used
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Mechanical – strain guage,
Thermal – thermistors,thermocouples
Magnetic – LVDT
Optical – photoconductive, solar
Acoustical - microphone
Chemical - pH
Nuclear – ionization chamber
Biological – ECG, EEG
Passive & Active transducer
Passive
Device which derive power reqd. for
transduction from auxiliary power source
- externally powered
Eg : resistive, inductive, capacitive
Without power they will not work
Active
They do not require external power source
Eg: solar cell
Analog & Digital transducer
Analog
• convert I/p quantity into an analog o/p
• Analog o/p- a continuous fn. Of time
• Eg. Strain gauge, L VDT, thermocouple
Digital
Converts I/p into an electrical o/p in the form
of pulses
Based on Electrical Principle
a) Variable – resistance type
1. Strain & pressure gauge 2) thermistors
3. Photoconductive cell 4) chemical conductive meter
b) Variable – inductance type
1. Linear Variable Differential Transformer (LVDT)
2. Eddy current gauge
c) Variable – capacitance type
1) Capacitor microphone 2) dielectric gauge 3)pressure gauge
d) Voltage – divider type
1) Potentiometer position sensor 2) pressure actuated voltage divider
e) Voltage generating type
1) Solar cell 2) Thermocouple
Tachometer
• A tachometer is a sensor device for measuring the rotation speed
of an object such as the engine shaft in a car. This device
indicates the revolutions per minute (RPM) performed by the
object.
Electromagnetic Flowmeter
• The principle of operation for the magnetic flowmeter is
based on the Faraday’s Law of Electromagnetic Induction.
Flowmeter
When a conductive liquid flows through the magnetic field, a small voltage (u) is
induced. This voltage is proportional to the velocity of the flow and is accurately
measured by two stainless steel electrodes mounted opposite each other inside
the metering pipe
LINEAR VARIABLE DIFFERENTIAL
TRANSFORMER(LVDT)
• AN LVDT transducer
comprises a coil former on to
which three coils are wound.
• The primary coil is excited
with an AC current, the
secondary coils are wound
such that when a ferrite core
is in the central linear
position, an equal voltage is
induced in to each coil.
• The secondary are connected
in opposite so that in the
central position the outputs
of the secondary cancels
each other out.
LVDT contd…
• The excitation is applied to the primary
winding and the armature assists the
induction of current in to secondary
coils.
• When the core is exactly at the center
of the coil then the flux linked to both
the secondary winding will be equal.
Due to equal flux linkage the
secondary induced voltages (eo1 &
eo2) are equal but they have opposite
polarities. Output voltage eo is
therefore zero. This position is called
“null position”
• Now if the core is displaced from its null
position toward sec1 then flux linked to
sec1 increases and flux linked to sec2
decreases. Therefore eo1 > eo2 and the
output voltage of LVDT eo will be positive
• Similarly if the core is displaced toward
sec2 then the eo2 > eo1 and the output
voltage of LVDT eo will be negative.
LVDT
• Advantages
• Applications
1. It gives higher o/p
voltage for small
changes in core position
2. Temp range-265oC to
600oC
3. It is available in
radiation resistant design
for operation in nuclear
reactors
1. In accelerometers
2. Jet engine control
3. Measurement of roll
position
4. Measurement of material
thickness in hot strip
Piezoelectric Transducer
In piezoelectric induction the measure and is converted into a
change in electrostatic charge q or voltage V generated by
crystals when mechanically it is stressed as shown in fig
Strain Gauge
• A strain gauge (or strain gage) is a device
used to measure strain on an object
• Applications
1. It is rugged, easy to use
2. In ac applications, it is capable ofmeasuring
variations upto 100KHz
3. It has a excellent linearity
4. It is less sensitive to shock and undesired
vibrations
5. It is available in multielement
Light dependent resistor (LDR)
Photojunction devices
phototransistor
photodiode
Photovoltaic Solar Cells
• Can convert about 20% of light power into
electricity
• Voltage is low (diode drop, ~0.6V)
Resistance Temperature Detectors
(RTDs)
Thermistor
• A
thermistor
is
a
type
of resistor whose resistance is
dependent on temperature, more so
than in standard resistors
• thermistor is generally a ceramic or
polymer
• the relationship between resistance and
temperature is linear
• R=KT
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•
•
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R- Change in resistance
T- Change in temperature
K- temperature coefficient of resistance
Thermistors can be classified into two types,
If is positive, the resistance increases with increasing temperature, and the
device is called apositive temperature coefficient (PTC) thermistor,
or posistor.
• If is negative, the resistance decreases with increasing temperature, and the
device is called a negative temperature coefficient (NTC) thermistor
• Advantages
1. It is chemically stable
2. Used in nuclear environment
3. Arranged in series-parallel
arrangement for increased
power handling capacity
4. Used for measuring temp
even at all places
inaccessible to other
thermometers
• Applications
1. Measuring temp
2. Thermal
conductivity
3. Attitude and wind
velocity
Thermocouple
• A thermocouple is a device consisting of two
dissimilar conductors or semiconductors that
contact each other at one or more points.
• A thermocouple produces a voltage when the
temperature of one of the contact points differs
from the temperature of another, in a process
known as the thermoelectric effect.
• Thermocouples are a widely used type
of temperature sensor for measurement and
control
Types
•
•
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Type E: (chromel – constantan) has a high output (68 µV/°C) which makes it well suited
to cryogenic use. Additionally, it is non-magnetic. Wide range is −50 °C to +740 °C and
Narrow range is −110 °C to +140 °C.
Type J : (iron – constantan) has a more restricted range (−40 °C to +750 °C) than type K, but
higher sensitivity of about 50 µV/°C. TheCurie point of the iron (770 °C) causes a smooth
change in the characteristic, which determines the upper temperature limit.
Type K : (chromel – alumel) is the most common general purpose thermocouple with a
sensitivity of approximately 41 µV/°C. It is inexpensive, and a wide variety of probes are
available in its −200 °C to +1350 °C / -330 °F to +2460 °F range
Type M: (Ni/Mo 82%/18% – Ni/Co 99.2%/0.8%, by weight) are used in vacuum furnaces for
the same reasons as with type C (described below). Upper temperature is limited to 1400 °C. It
is less commonly used than other types.
Type N: (Nicrosil – Nisil) thermocouples are suitable for use between −270 °C and +1300 °C
owing to its stability and oxidation resistance. Sensitivity is about 39 µV/°C at 900 °C, slightly
lower compared to type K.
Type T (copper – constantan) : thermocouples are suited for measurements in the −200 to
350 °C range
Chromel – gold/iron alloy thermocouples
Tungsten/rhenium alloy thermocouples
Platinum/rhodium alloy thermocouples
Microphone
A microphone is a type of transducer.
Early microphones were invented for
communication purposes.
Later modifications were made to design as
the microphone was used more in
entertainment industry.
Overview of a Microphone


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Diaphragm—part of microphone which receives the
vibration from sound waves.
Thickness and material of diaphragm are changed
depending on the sound waves you wish to pick up.
How it works?

Electrical circuit is used to change these
detected vibrations into an electrical
signal that “images” the sound with an
output voltage or current.
Characteristics of Microphone
Requisites of a good microphone
• High sensitivity
• High SNR
• Flat frequency response over most of the audible
frequency range
• Very low distortion
• It should have correct o/p impedance to match the
with the line impedance
• The directivity of the microphone should be such
as to meet the requirement of application
Different Types of Microphones
1.
2.
3.
4.
5.
6.
7.
Carbon
Ribbon
Moving Coil
Crystal
Ceramic
Capacitor
Electret
Carbon Microphone—Historical
Design
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
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Thomas Alva Edison and
Sir Emile Berliner filled
patents for Carbon Button
Microphone in 1877.
Edison's design became the
accepted design and patent.
This is a popular
microphone for telephones
as well as early radio and
speeches.
Carbon microphone—Design
Diagram
Ribbon Microphone
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
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Diaphragm: Thin piece of
metal foil suspended in a
magnetic field.
Vibrations in ribbon
produce a small voltage
which is then stepped up
by a transformer.
Diaphragm is very easily
damaged by wind or loud
incoming sounds.
Ribbon Microphone—
Design Diagram
Moving Coil Microphone
Crystal Microphone
Ceramic Microphone
Capacitor Microphone
The Electret Microphone
It is similar to capacitor microphone that it does not require
A polarization voltage for its capacitor
Loudspeaker
It is a transducer which convert electrical signal to sound wave
Loudspeaker
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