Sensors are a kind of electronic components that detect the presence or absence of something. Depending upon the sensitivity of a sensor, it can also detect changes that happen with respect to time.
There is also a thing called transducer that works very similar to a sensor but both of them have significant differences.
Transducer: A transducer is a component that is capable to convert energy of one kind to another one. Equipped with a sensor, transducer produces human readable data to what we call as the output of the sensor.
Thus, we can understand that a Sensor is not a perfect sensor unless it is coupled with a transducer. Sensor detects whatever it has to detect and transducers then convert that recognized energy into a readable and understandable data that we get as output.
Sensors are grouped into two major categories:
Active Sensors: These sensors do not need a separate power supply to work because the energy sensed by these sensors does not affect their electrical properties. These sensors are okay to work on the energy that has been sensed.
Passive Sensors: These sensors need a separate power supply to work because the energy sensed by these sensors often affects their electrical properties like: resistance, inductance, capacitance etc.
Though there may be numerous sensors but the most common for IoT ecosystem are as follows:
Temperature Sensors: Temperature Sensor is used to sense a significant rise and fall in the temperature of an object. Since a very long while, Mercury based thermometers are being used but later on, many semiconductor-based temperature sensors have been developed.
Thermocouples, RTDs (Resistor Temperature Detectors) or Thermostats are various examples of temperature sensors.
Proximity Sensors: Proximity sensors are used to detect physical presence or absence of something relative to an object. These sensors have a very big use case in vehicles. Proximity sensors are attached to the bumpers and side walls of vehicles so that it can notify the driver whenever another vehicle comes nearby.
Inductive sensors, capacitive sensors, photoelectric sensors and ultrasonic sensors are used as proximity sensors.
Pressure Sensors: Pressure sensors are used to detect an increase or a drop in the pressure that is applied on them. These sensors are used in gas filled cylinders in order to detect whether the pressure in the supply pipe is okay or not.
Chemical Sensors: Chemical sensors are used to detect any chemical changes that happen to an element. In chemical factories, these sensors are always busy detecting any leakage of hazardous chemicals. Even water quality is also detected using chemical sensors.
Gas Sensors: Gas sensors are also a type of chemical sensors but are used specifically for detecting presence of different gases. These sensors play a vital role in factories where chemical formulations are made.
CO2 sensors, CO sensors, Breathalyzers, Air pollution sensors, hygrometers, smoke sensors etc. are different gas sensors.
Level Sensors: Level sensors are used to detect any rise or fall in the level of fluids. Especially in containers that contain gigantic fluids like petroleum products or water, level sensors are used to detect the consumption and remains.
Image Sensors: Image sensors are those that detect a scene and produce some digital data depicting that. These sensors are used widely in digital cameras, biometric devices, medical imagery and night-vision equipment. CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) are the most common image sensing techniques.
Motion Detection Sensors: These sensors are used to detect whether an object is standing or is in motion. Motion detection is on supreme priority when it comes to security breaches. Even on assembly lines in industries, where automated robo-arms are functioning, motion detection sensors are used to keep track of the precision required in moving parts.
Accelerometer Sensors: These sensors are used to detect acceleration in moving things. Now a days, accelerometers are used in many smart gadgets like, smartphones, earbuds, smartwatches etc.
Hall Effect accelerometers, capacitive accelerometers and piezoelectric accelerometers are most common sensors of this kind.
Gyroscope Sensors: Gyroscope sensors are used to detect angular positioning and angular motion of an object. Gyroscope is also pretty common in a variety of gadgets like smartphones, smart watches etc.
Optical Sensors: Optical sensors detect presence or absence of light in a space. The most common use case of optical sensors is in home security systems. LDR (Light Detecting Resistance) is a semiconductor component that is used primarily as an optical sensor.