Physical variables and transducer

unit 3
Physical Variables and transducers 

Sensor

Sensors are electrical devices that have the capability of sensing different physical variables. The sensor may be classified on different bases one of them is a physical quantity. Hence on the basis of a physical quantity or physical vibration involved the sensors are classified as:

• Resistive sensor 

The input being measured is transformed into a change in resistance.

examples: potentiometer, resistance thermometer, strain gauge, etc.

• Inductive sensor

The input being measured is transformed into a change in resistance.

example LVDT.

• Capacitive Sensor

The input being measured is transformed into a change in capacitance.

example: capacitive Displacement sensor.

On the basis of power supply required:

• Active Sensor

Active sensors are those which do not require an external power supply. 

example: thermo-couple

• Passive Sensor

Passive Sensors are those which require a power supply.

example: Potentiometer.

Physical variables and their types

The measurement of any instrumentation system makes its first contact with primary sensing element or an input device.

The physical variables are the quantities required to be measured. All these quantities require primary detection elements to be converted into another analogous form which is acceptable by a later stage of the measurement system.