Unit 2
Introduction of Transducers
Introduction, Advantages and Disadvantages of Electrical Transducers,
Classification of Transducers, Static and Dynamic characteristics. Principle
of measurement of displacement. Resistive potentiometers, variable
inductance & variable reluctance pickups, LVDT.
Introduction to Transducers
› A transducer is any device that converts one form of energy
into another.
› Examples of common transducers include the following:
› A microphone converts sound into electrical impulses and a
loudspeaker converts electrical impulses into sound (i.e., sound
energy to electrical energy and vice versa).
› A solar cell converts light into electricity and a thermocouple
converts thermal energy into electrical energy.
› An incandescent light bulb produces light by passing a current
through a filament. Thus, a light bulb is a transducer for
converting electrical energy into optical energy.
› An electric motor is a transducer for conversion of electricity
into mechanical energy or motion..
Advantages of Electrical Transducers
› Electrical signal obtained from electrical transducer can be easily processed
(mainly amplified) and brought to a level suitable for output device which
may be an indicator or recorder.
› The electrical systems can be controlled with a very small level of power
› The electrical output can be easily used, transmitted, and processed for the
purpose of measurement.
› With the advent of IC technology, the electronic systems have become
extremely small in size, requiring small space for their operation.
› No moving mechanical parts are involved in the electrical systems. Therefore
there is no question of mechanical wear and tear and no possibility of
mechanical failure.
› Electrical transducer is almost a must in this modem world. Apart from the
merits described above, some disadvantages do exist in electrical sensors.
Disadvantages of Electrical Transducers
› The electrical transducer is sometimes less reliable than mechanical
type because of the ageing and drift of the active components.
› Also, the sensing elements and the associated signal processing circuitry
are comparatively expensive.
› With the use of better materials, improved technology and circuitry, the
range of accuracy and stability have been increased for electrical
transducers.
› Using negative feedback technique, the accuracy of measurement and
the stability of the system are improved, but all at the expense of
increased circuit complexity, more space, and obviously, more cost.
Transducers
Transducers : Signal Conditioning Unit
• Analog to Digital Converters
• Amplifiers
• Filters
• Rectifiers
• Modulators
Classification of Transducers
Classification of Transducers
1. based on the Principle of Transduction
• The transducer is classified by the transduction medium.
• The transduction medium may be resistive, inductive or capacitive depends on the conversion
process that how input transducer converts the input signal into resistance, inductance and
capacitance respectively.
2. Primary and Secondary Transducer
• Primary Transducer – The transducer consists the mechanical as well as the electrical
devices. The mechanical devices of the transducer change the physical input quantities
into a mechanical signal. This mechanical device is known as the primary transducers.
• Secondary Transducer – The secondary transducer converts the mechanical signal into
an electrical signal. The magnitude of the output signal depends on the input
mechanical signal.
Classification of Transducers
3. Passive and Active Transducer
• Passive Transducer – The transducer which requires the power from an external
supply source is known as the passive transducer. They are also known as the external
power transducer. The capacitive, resistive and inductive transducers are the example
of the passive transducer.
• Active Transducer – The transducer which does not require the external power source
is known as the active transducer. Such type of transducer develops theirs owns
voltage or current, hence known as a self-generating transducer. The output signal is
obtained from the physical input quantity.
The physical quantity like velocity, temperature, force and the intensity of light is induced
with the help of the transducer. The piezoelectric crystal, photo-voltaic cell, tacho
generator, thermocouples, photovoltaic cell are the examples of the active transducers
Classification of Transducers
4. Analog and Digital Transducer
The transducer can also be classified by their output signals. The output signal of the
transducer may be continuous or discrete.
Analog Transducer – The Analog transducer changes the input quantity into a continuous
function. The strain gauge, L.V.D.T, thermocouple, thermistor are the examples of the
analogue transducer.
Digital Transducer – These transducers convert an input quantity into a digital signal or in
the form of the pulse. The digital signals work on high or low power.
Classification of Transducers
5. Transducer and Inverse Transducer
• Transducer – The device which converts the non-electrical quantity into an
electric quantity is known as the transducer.
• Inverse Transducer – The transducer which converts the electric quantity into a
physical quantity, such type of transducers is known as the inverse transducer.
The transducer has high electrical input and low non-electrical output.
Measurement of Displacement
Measurement of displacement using Resistive Transducer , Inductive Transducer, Capacitive
Transducer.
1. Measurement of Displacement using Resistive Transducer
The circuit diagram of resistive transducer, which is used to measure displacement is shown in below
figure.
Measurement of Displacement
Measurement of displacement using Resistive Transducer , Inductive Transducer, Capacitive
Transducer.
1. Measurement of Displacement using Capacitive Transducer
The circuit diagram of resistive transducer, which is used to measure displacement is shown in below
figure.
Measurement of Displacement
3. Measurement of Displacement using Inductive Transducer Transducer
The circuit diagram of Inductive transducer, which is used to measure displacement is shown in
below figure.
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