Something that changes during an experiment is called physical variable. A physical variable is something that is bound to change and not constant.
A transducer is an electronic device that converts energy from one form to another..It is also called sensors in general. An electrical transducer is a device which is capable of converting the physical quantity into a proportional electrical quantity such as voltage or electric current. Hence, it converts any quantity to be measured into the usable electrical signal. This physical quantity which is to be measured can be pressure, level, temperature, displacement etc. The output which is obtained from the transducer is in the electrical form and is equivalent to the measured quantity. For example, a temperature transducer will convert temperature to an equivalent electrical potential. This output signal can be used to control the physical quantity or display it. Transducers are often employed at the boundaries of automation ,measurement , and control systems, where electrical signals are converted to and from other physical quantities (energy, force, torque, light, motion, position, etc.). The process of converting one form of energy to another is known as transduction.
Classification of transducer/sensor:
On the basis of power supply, Sensors can be classified as:
Passive sensors are those which acquires some external power supply for their operation.eg-Resistive sensors, inductive sensors ,capacitive sensors etc.Active sensors are those which doesn’t acquire external power supply for their operation.eg-piezoelectric sensors, thermoelectric sensors etc.
On the basis of applications, Sensors can be classified as Displacement sensors, gas sensors, temperature sensors, humidity sensors, moisture sensors etc.
On the basis of Physical principle involved , Sensors can be classified as:
On the basis of nature of output signal , Sensors can be classified as:
1.S.morris.alan(2001). Measurement and Instrument principle(3 ed.).A division of Reed Educational and Professional Publishing Ltd