• 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. ... In a mercury-based glass thermometer,
the input is temperature.
3. INTRODUCTION OF TRANSDUCERS
• A transducer is a device that convert one form of energy to other form. It
converts the measurand to a usable electrical signal.
• A transducer is a device which transforms a non-electrical physical quantity (i.e.
temperature, sound or light) into an electrical signal (i.e. voltage, current,
• In other word it is a device that is capable of converting the physical quantity into
a proportional electrical quantity such as voltage or current.
4. BLOCK DIAGRAM OF TRANSDUCERS
• Transducer contains two parts that are closely related to each other i.e. the sensing
element and transduction element.
• The sensing element is called as the sensor. It is device producing measurable
response to change in physical conditions.
• The transduction element convert the sensor output to suitable electrical form.
6. CLASSIFICATION OF TRANSDUCERS
The transducers can be classified as:
I. Active and passive transducers.
II. Analog and digital transducers.
III. On the basis of transduction principle used.
IV.Primary and secondary transducer
V. Transducers and inverse transducers.
7. Active transducers :
• These transducers do not need any external source of power for their operation.
Therefore they are also called as self generating type transducers.
• The active transducer are self generating devices which operate under the energy
• As the output of active transducers we get an equivalent electrical output signal
e.g. temperature or strain to electric potential, without any external source of
energy being used.
9. Passive Transducers :
I. These transducers need external source of power for their operation. So they
are not self generating type transducers.
II. A DC power supply or an audio frequency generator is used as an external
III. These transducers produce the output signal in the form of variation in
resistance, capacitance, inductance or some other electrical parameter in
response to the quantity to be measured.
12. PRIMARY AND SECONDARY
• Some transducers contain the mechanical as well as electrical device.
The mechanical device converts the physical quantity to be measured
into a mechanical signal. Such mechanical device are called as the
primary transducers, because they deal with the physical quantity to be
• The electrical device then convert this mechanical signal into a
corresponding electrical signal. Such electrical device are known as
secondary transducers. (eg. potentiometer – transforms displacement
14. CLASSIFICATION OF TRANSDUCERS
Transducer and Inverse Transducer
•Transducers convert non electrical quantity to electrical quantity.
• Inverse transducers convert electrical quantity to a non electrical quantity
17. VARIABLE RESISTANCE TRANSDUCERS
• The variable resistance transducers are one of the most commonly
used types of transducers. The variable resistance transducers are
also called as resistive transducers or resistive sensors.
• They can be used for measuring various physical quantities like
temperature, pressure, displacement, force, vibrations etc.
• These transducers are usually used as the secondary transducers,
where the output from the primary mechanical transducer acts as the
input for the variable resistance transducer.
18. Principle of Working of Variable Resistance
• The variable resistance transducer elements work on the principle
that the resistance of the conductor is directly proportional to the
length of the conductor and inversely proportional to the area of the
conductor. Thus if L is the length of the conductor (in m) and A is its
area (in m square), its resistance (in ohms) is given by:
• R = ρL/A
• Where ρ is called as resistivity of the material and it is constant for
the materials and is measured in ohm-m.
• The resistance of some materials also changes with the change in
their temperature. This principle is primarily used for the
measurement of temperature.
20. SLIDING CONTACT DEVICES
• Sliding contact resistive transducers convert a mechanical
displacement input into an electrical output, either voltage or
• This is accomplished by changing the effective length L of the
conductor. Some form of electric resistance element is used with
which a brush maintains electrical contact as it moves.
• In simple, the device may consist of a stretched wire and slider.
• The effective resistance existing between either end of the wire and
the brush thereby becomes a measure of the mechanical
• Devices of this type are used to measure larger displacements.
25. RESISTANCE STRAIN GAUGE
• A strain gauge is a device used to measure strain on an object. The most common type of
strain gauge consists of an insulating flexible backing which supports a metallic foil pattern.
• The gauge is attached to the object by a suitable adhesive. As the object is deformed, the foil
is deformed, causing its electrical resistance to change.
• This resistance change, usually measured using a Wheatstone bridge, is related to the strain
by the quantity known as the gauge factor.
• A strain gauge takes advantage of the physical property of electrical conductance and its
dependence on the conductor's geometry.
• When an electrical conductor is stretched within the limits of its elasticity such that it does
not break or permanently deform, it will become narrower and longer, which increases its
electrical resistance end-to-end.
• Conversely, when a conductor is compressed such that it does not buckle, it will broaden and
shorten, which decreases its electrical resistance end-to-end. From the measured electrical
resistance of the strain gauge, the amount of induced stress may be inferred.
26. • The Strain Gauge is an example of a passive transducer that uses
electrical resistance variation in wires to sense the strain produced by
a force on the wire.
• It is a very versatile detector and transducer for measuring weight,
pressure, mechanical force or displacement.
33. What is Inductor?
If a time varying current flows through a coil there is an emf induced
in it. The induced emf across the coil is directly proportional to the rate of
change of current with respect to time. Due to the property inducing emf,
all types of electrical coil can be referred as inductor. An inductor is an
energy storage device which stores energy in form of magnetic field.
What is Inductance?
The induced emf across a coil is directly proportional to the rate of
change of current through it. The proportionality constant in that relation is
known as inductance.
47. Capacitance is the ability of a component or circuit to collect and store
energy in the form of an electrical charge.
Capacitors are energy-storing devices available in many sizes and shapes.
They consist of two plates of conducting material (usually a thin metal)
sandwiched between an insulator made of ceramic, film, glass or other
materials, even air.