Sensor

Sensor are devices that perform input function in a system as they sense the changes in quantity.

The best example of a sensor is mercury thermometer.

A sensor is a device which can quantitatively measure a certain physical quantity and converts a physical quantity into an electrical signal.

Classification of Sensor

All the sensor can be classified into two types based on the power or signal requirement. They are Active sensor and passive sensor.
Active Sensor:
- this type of sensor produce output signal with help of external excitation supply. In order to operate active sensor, require power signal from an external source.
- Strain gauge is an example of active sensor.
Passive Sensor:
- it produces output signal without the help of external excitation supply. They do not need any extra stimulus or voltage.
- A thermocouple is a passive sensor which generates a voltage value corresponding to heat, applied. It does not need any power supply.

Types of Sensor

1. Position : a position sensor measures the position of an object; the position measurement can be either in absolute terms (absolute position sensor) or in relative terms (displacement sensor). Position sensors can be liner, angular, or multi-axis.

2. Occupancy and motion : Occupancy sensor detects the presence of people and animals in surveillance area, while motion sensor detects movement of people and object.

3. Velocity and Acceleration : Velocity (speed of motion) sensor may be linear or angular, indicating how fast an object moves along a straight line or how fast it rotates.

4. Force : Force sensor detects whether a physical force is applied and whether the magnitude of force is beyond a threshold. Example touch sensor.

5. Pressure : Pressure sensor are related to force sensor and measure the force applied by liquids or gases.

6. Flow : Flow sensor detect the rate of fluid flow. They measure the volume (mass flow) or rate (flow velocity) of fluid that has passed through a system in a given period of time.

7. Acoustic : Acoustic sensor measure sound levels and convert that information into digital or analog data signal.

8. Humidity : Humidity is defined as the amount of water present in the surrounding air.

9. Light : Light sensor detects the presence of light. For example infrared sensor, photo detector.

10. Radiation : Radiation sensor detect radiations in the environment. Radiation can be sensed by scintillating or ionization detection.

11. Temperature : Temperature sensor measure the amount of heat or cold that is present in a system.

12. Chemical : Chemical sensor measure the concentration of chemicals in a system.

13. Image : Image sensor are instruments which are used to convert optical image into electronic signal for displaying or storing files electronically. For example thermal image device, radar, sonar, biometric etc.

14. Optical : Optical sensor measure the physical quantity of light rays and covert it into electrical signal which cab be easily readable by user or an electronic instrument/device is called optical sensor. For example fiber optics, Pyrometer, photo detector etc.

15. Gas : gas sensor plays a major role in detecting the gas leakage. These gas sensor are classified into various type based on the type of gas that to be detected.

16. Ultrasonic : ultrasonic means the range of the frequencies. Its range is greater than audible range (>20 kHz) so even it is switched on, you can’t sense these sound signals.

17. Hall : Hall sensor is used to detect the magnetic field and gives output in terms of voltage.

18. Infrared Sensor (IR) : it is used to certain characteristics of its surroundings by either emitting or detecting infrared radiation.

19. Biosensors : Biosensor detects various biological elements such as organisms, tissue, cells, enzymes, antibodies,

20. Micro and nano-sensors : micro sensor (sometimes also called MEMS) are the miniaturized version of the conventional macro sensor with improved performance and reduced cast.

Criteria to Choose a Sensor

Range
Resolution
Accuracy
Precision
Sensitivity
Ruggedness
Linearity
Hysteresis
Response Time
Bandwidth
Resonance
Stability
Repeatability
Cost
Power Consumption
Type of Sensing
Signal-to-noise ratio
Operating Temperature