Sensors are classified into various categories based on different considerations. The criteria for considerations may be any one of the following.
Primary measured quantity
Depending on the physical parameter to be measured, sensors may be of different types. To measure temperature the sensor will be a temperature sensor; for measuring light intensity, it will be a light sensor, etc.
Using physical and chemical effects: The principle based upon which the sensor converts the physical parameters to be measured into appropriate signal, is also a classification criterion for sensors. The presence of metal may be detected by using the electromagnetic principle. In that case, the sensor’s transduction is based on electromagnetic induction. In some other cases, chemical effects may be utilized in the transduction process. Therefore sensors for different types of transductions may be classified accordingly
Material and Technology
Sensors are made of different materials and their technology of applications is widely varied. So sensors may be also classified based on used materials and technology.
Sometimes sensors are selected based on the prominent physical property that is present in the observed phenomenon. In some cases the desired parameter may not be possible to take in the phenomena but some other parameters may be more convenient to sense which will give the target measurement in some alternative way. The observer must find the relationship between the measured parameter and the desired parameter. For example rate of respiration is quantified by observing the rate of change of chest volume of a patient by employing image sensor along with image processing technique. However the target output is not to find the rate of respiration but the overall state of health of the patient.