Explaining the difference between the transduscers , sensors and actuators

1. Transducers , Sensors & Actuators
According to the opinion of some experts, a transducer is a device which
transforms non-electrical energy into electrical energy or vice versa. Another
definition of this term transducer is a device which transforms energy from one
domain into another. Typical energy domains are mechanical, electrical, chemical,
fluid, and thermal. A transducer can be defined also as a device which transforms
energy from one type to another, even if both energy types are in the same
domain.
According to the above definitions, transducer is a device that converts a signal
from one physical form to a corresponding signal having a different physical form.
Therefore it is an energy converter. This means that the input signal always has
energy or power.
Transducers may generally be divided into two class – Sensors, which monitor the
system – Actuators, which impose a condition on a system. Sensors and actuators
are comprehensive classes of transducers. Some transducers can operate as a
sensor or as a actuator, but not as both simultaneously.
Sensor examples: – Hotwire anemometers (measure flow velocity) – Microphones
(measure fluid pressure) – Accelerometers (measure the acceleration of a
structure) – Gas sensors (measure concentration of specific gas or gases) –
Humidity sensor – Temperature sensors, etc
Actuator examples – Motors (which impose a torque) – Force heads (which
impose a force) – Pumps (which impose either a pressure or a fluid velocity).

2. Any device converting signal of one kind to signal of a different kind is considered
to be a transducer. The output signals can be of any useful physical form. The
transducer can be placed as input transducer or output transducer. An input
transducer converts physical signal to electric signal while an output transducer
converts electric signal to physical signal.
Another name of input and output transducers are sensor and actuator. Sensor is
used to refer to the input transducer while actuator refers to the output
transducer. Sensors are intended to acquire information, usually designed to
handle low power and intended to consume energy as low as possible. Actuators
are designed to power conversion and to handle (relatively) high power.
In other words, The word “Transducer” is the collective term used for both
Sensors which can be used to sense a wide range of different energy forms such
as movement, electrical signals, radiant energy, thermal or magnetic energy etc,
and Actuators which can be used to switch voltages or currents.
There are many different types of sensors and transducers, both analogue and
digital and input and output available to choose from. The type of input or output
transducer being used, really depends upon the type of signal or process being
“Sensed” or “Controlled” but we can define a sensor and transducers as devices
that converts one physical quantity into another.
Devices which perform an “Input” function are commonly called Sensors because
they “sense” a physical change in some characteristic that changes in response to
some excitation, for example heat or force and covert that into an electrical
signal. Devices which perform an “Output” function are generally called Actuators
and are used to control some external device, for example movement or sound.

3. Electrical Transducers are used to convert energy of one kind into energy of
another kind, so for example, a microphone (input device) converts sound waves
into electrical signals for the amplifier to amplify (a process), and a loudspeaker
(output device) converts these electrical signals back into sound waves and an
example of this type of simple Input/Output (I/O) system is given below.