What Are Sensors & Transducers ? Difference Between Active & Passive Transducer - SKengineers

 

SENSORS AND TRANSDUCERS

Ø  SENSORS :

·        A sensor is defined as an element which when subjected to some physical change experiences a relative change.

·        Devices which respond directly to any physical phenomenon such as force, temperature, heat, light etc. are called sensors.

·        The sensor produces a proportional output signal mechanical, electrical or magnetic when exposed to physical phenomenon.

Ø  CLASSIFICATION OF SENSORS :

·       

Sensors can be classified into various groups according to the factors such as measurand, application field, conversion principle, energy domain of the measurand and thermodynamic considerations.

·        Detail classification of sensors in view of their applications in manufacturing is as follows.

A.     Displacement, position and proximity sensors :-

1.      Potentiometer

2.      Strain gauged element

3.      Capacitive element

4.      Differential transformers

5.      Eddy current proximity sensor

6.      Inductive proximity switch

7.      Optical encoders

8.      Pneumatic sensors

9.      Proximity switch (magnetic)

10.   Hall effect sensors

B.     Velocity and motion sensors :-

1.      Incremental encoder

2.      Tacho-generator

3.      Pyroelectric sensors

C.      Force sensor :-

1.      Strain gauge load cell

D.     Fluid pressure sensors :-

1.      Diaphragm pressure gauge

2.      Capsules, bellows, pressure tubes

3.      Piezoelectric sensors

4.      Tactile sensor

E.      Liquid flow sensor :-

1.      Orifice plate

2.      Turbine meter

F.      Liquid level sensor :-

1.      Floats

2.      Differential pressure

G.     Temperature sensors

1.      Bimetallic strips

2.      Resistance temperature detectors

3.      Thermistors

4.      Thermo-diodes and transistors

5.      Thermocouples

6.      Light sensors

7.      Photo diodes

 

 

 

Ø  TRANSDUCERS :

·        Transducers are device which converts one form of energy into other form of energy.

·        For example , microphones, thermometers, position and pressure sensors and antenna ; LEDs etc.

·        The term transducer is synonymously used with sensors although the principles are different.

·        Transducers are physical element and is an essential part of sensor.

·        The transducers refers to sensing element along with signal conditioning circuitry.

Ø  CLASSIFICATION OF TRANSDUCERS :

1.      ACTIVE TRANSDUCERS :-

·        The transducer which generates an electrical signal directly in response to the physical parameter being measured are called as active transducers.

·        Active transducers are self -generating devices i.e. they does not require an external power source for its operation. Active transducers operate under energy conversion principle that generates an equivalent output signal.

v  EXAMPLES :

a)      Photo voltaic cells

b)     Thermocouples

c)      Piezoelectric transducer

2.      PASSIVE TRANSDUCER :-

·        The transducer which requires external energy source for its operation is called as passive transducer.

·        Passive transducer works under energy controlling principle, which makes it necessary to use an external electrical source for its operation.

v  EXAMPLES :-

a)      Thermistor

b)     Strain gauge

c)      Load cell

 

COMPARISON BETWEEN ACTIVE TRANSDUCER AND PASSIVE TRANSDUCER

Sr. No.	ACTIVE TRANSDUCER	PASSIVE TRANSDUCER
1.	Active transducer generates an equivalent electrical output signal without any external energy source.	Passive transducer produces change in electrical parameter i.e. R, I, and C.
2.	Additional external energy input source is not required.	Additional external energy input source is required for its operation.
3.	It operates under energy conversion principle.	It operates under energy controlling principle.
4.	Complicated design and costly transducer.	Simple design and economical.
5.	EXAMPLE : piezoelectric , transducer, thermocouple, photovoltaic cell.	EXAMPLE : strain gauge, thermistor, load cell.