Sensors and Sensor Types


Definition of sensor 

A sensor is a device that detects and responds to some type of input from the physical environment. The specific input could be light, heat, motion, moisture, pressure, or any one of a great number of other environmental phenomena. 
A sensor is a device that detects and responds to some type of input from the physical environment. The specific input could be light, heat, motion, moisture, pressure, or any one of a great number of other environmental phenomena. The output is generally a signal that is converted to human-readable display at the sensor location or transmitted electronically over a network for reading or further processing. 

What is a Sensor?

There are numerous definitions as to what a sensor is but I would like to define a Sensor as an input device which provides an output (signal) with respect to a specific physical quantity (input). The term “input device” in the definition of a Sensor means that it is part of a bigger system which provides input to a main control system (like a Processor or a Microcontroller).
Another unique definition of a Sensor is as follows: It is a device that converts signals from one energy domain to electrical domain. The definition of the Sensor can be better understood if we take an example in to consideration.
The simplest example of a sensor is an LDR or a Light Dependent Resistor. It is a device, whose resistance varies according to intensity of light it is subjected to. When the light falling on an LDR is more, its resistance becomes very less and when the light is less, well, the resistance of the LDR becomes very high. We can connect this LDR in a voltage divider (along with other resistor) and check the voltage drop across the LDR. This voltage can be calibrated to the amount of light falling on the LDR. Hence, a Light Sensor.
Now that we have seen what a sensor is, we will proceed further with the classification of Sensors.

Classification of Sensors

There are several classifications of sensors made by different authors and experts. Some are very simple and some are very complex. The following classification of sensors may already be used by an expert in the subject but this is a very simple classification of sensors. In the first classification of the sensors, they are divided in to Active and Passive. Active Sensors are those which require an external excitation signal or a power signal. Passive Sensors, on the other hand, do not require any external power signal and directly generates output response. The other type of classification is based on the means of detection used in the sensor. Some of the means of detection are Electric, Biological, Chemical, Radioactive etc. The next classification is based on conversion phenomenon i.e., the input and the output. Some of the common conversion phenomena are Photoelectric, Thermoelectric, Electrochemical, Electromagnetic, Thermooptic, etc. The final classification of the sensors are Analog and Digital Sensors. Analog Sensors produce an analog output i.e., a continuous output signal (usually voltage but sometimes other quantities like Resistance etc.) with respect to the quantity being measured. Digital Sensors, in contrast to Analog Sensors, work with discrete or digital data. The data in digital sensors, which is used for conversion and transmission, is digital in nature.

Types of Sensors

  • Infrared Sensor(IR Sensor)
  • Temperature & Thermocouple Sensors
  • Proximity Sensor
  • Ultrasonic sensor
  • Accelerometers & Gyroscope Sensor
  • Pressure Sensor
  • Hall Effect Sensor
  • Load cell
  • Light Sensor
  • Color Sensor
  • Touch Sensor
  • Tilt Sensor
  • PIR Motion Detector & Vibration Sensor
  • Metal detector, Water Flow & Heartbeat Sensor
  • Flow and Level Sensor
  • Smoke, Fog, Gas, Ethanol & Alcohol Sensor
  • Humidity, Soil Moisture & Rain Sensor

Infrared Sensor(IR Sensor)

An infrared sensor is an electronic device, that emits in order to sense some aspects of the surroundings. An IR sensor can measure the heat of an object as well as detects the motion. These types of sensors measure only infrared radiation, rather than emitting it that is called a passive IR sensor. 


  • It uses less power
  • The detection of motion is possible in the presence or absence of light approximately with equal reliability.
  • They do not need contact with the object for detection
  • There is no data leakage because of the ray direction
  • These sensors are not affected by oxidation & corrosion
  • Noise immunity is very strong


  • Line of sight is required
  • Range is limited
  • These can be affected by fog, rain, dust, etc
  • Less data transmission rate


  • Obstacle detector 
  • In robotics 
  • Brightness comparison 
  • Distance measurement

Temperature & Thermocouple Sensors>>

Temperature Sensors

A temperature sensor is an electronic device that measures the temperature of its environment and converts the input data into electronic data to record, monitor, or signal temperature changes. 

Industrial Applications of Temperature Sensor

  • Boiler Units
  • Power and Utility Stations
  • Mining and Drilling
  • Energy Generation and Distribution
  • Medical Laboratories and Examination
  • Industrial Process Monitoring

Thermocouple Sensors

A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference.

A thermocouple is a temperature-measuring device consisting of two dissimilar conductors that contact each other at one or more spots. It produces a voltage when the temperature of one of the spots differs from the reference temperature at other parts of the circuit.

Thermocouples Advantages 

  • Simple, Rugged 
  • High temperature operation 
  • Low cost 
  • No resistance lead wire problems 
  • Point temperature sensing 
  • Fastest response to temperature changes 

Thermocouples Disadvantages 

  • Least stable, least repeatable 
  • Low sensitivity to small temperature changes
  • Extension wire must be of the same thermocouple type 
  • Wire may pick up radiated electrical noise if not shielded 
  • Lowest accuracy

Thermocouple Applications 

  • Plastic injection molding machinery 
  • Food processing equipment 
  • Deicing 
  • Semiconductor processing 
  • Heat treating 
  • Medical equipment 
  • Industrial heat treating 
  • Packaging equipment

Proximity Sensor

A proximity sensor detects an objects when the object approaches within the detection range and boundary of the sensor.  Proximity sensors include all sensor that perform non contact detection in comparison to sensors such as limit switch, that detects the object by physically contacting them. Proximity sensors are used in various facets of manufacturing for detecting the approach of metal and non metal objects.


  • It can detect both metallic and non metallic targets. 
  • Good stability 
  • High Speed 
  • Capacitive sensors are good in terms of power usage 
  • Low cost 


  • They are affected by temperature and humidity 
  • Difficulties in designing 
  • Capacitive proximity sensors are not as accurate compare to inductive sensors.

Proximity Sensor Applications 

  • Used on automated production lines for object detection, position, inspection, and counting.
  • Proximity sensors are used in smartphones
  • Part detection on industrial conveyor systems.
  • Collision detection on robots.
  • Capacitive proximity sensors are used as touch switches on consumer electronics products.
  • Diffuse sensors are used in public washrooms to control water flow.

Ultrasonic sensor

The ultrasonic sensor sends out sound and receives it back using the receiver. Together, the ultrasonic sensor's sender and receiver look like a pair of eyes, but it is not a sight sensor. Instead, those "eyes" are really more like a speaker and a microphone (a sound sensor).


  • Ultrasonic proximity sensors are not affected by atmospheric dust, snow, rain..etc 
  • Can work in adverse conditions 
  • Sensing distance is more compared to inductive or capacitive proximity sensors 


  • Ultrasonic sensors Has More Difficulties Reading Reflections From Soft, Curved, Thin Or Small Objects.

Accelerometers & Gyroscope Sensor>>

Accelerometer Sensor

An accelerometer is an electro- mechanical device that measures proper acceleration forces. These forces may be static like the constant force of gravity pulling at your feet, or they could be dynamic – caused by moving and vibrating the accelerometer.


  • Rugged and Inexpensive
  • High Impedance
  • High sensitivity
  • High frequency response 


  • Sensitive to temperature
  • Hysteresis error
  • Less longevity
  • Decreased efficiency with time

Application of Accelerometer

  • Acceleration and vibration calculation in vehicles
  • In industries for monitoring machines
  • Building and structural monitoring
  • Medical application and navigation
  • Transport

Gyroscope Sensor

A gyroscope is a device for measuring or maintaining orientation, based on the principles of conservation of angular momentum.

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Pressure Sensor

A pressure sensor is a device for pressure measurement of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical.


  • Pressure sensing
  • Altitude sensing
  • Flow sensing
  • Level / depth sensing
  • Leak testing

Hall Effect Sensor

The basic Hall Element of the Hall Effect magnetic sensors mostly provides very small voltage of only a few micro volts per Gauss, so therefore, these devices are usually manufactured with built-in high gain amplifiers.

Applications of Hall Effect Sensor

  • When combined with threshold detection they act as a switch.
  • These are used in ultra-high-reliability applications such as keyboards.
  • Hall Effect sensors are used to time the speed of wheels and shafts.
  • These are used to detect the position of permanent magnet in brushless electric DC motors.
  • Hall Effect sensors are embedded in digital electronic devices along with linear transducers.
  • Sensing the presence of the magnetic field in industrial applications.
  • Used in smartphone to check whether the flip cover accessory is closed.
  • For contactless measurement of DC current in current transformers, Hall Effect sensor is used.
  • This is used as a sensor to detect the fuel levels in automobiles.

Load cell

A load cell is a transducer which converts force into a measurable electrical output. Although there are many varieties of force sensors, strain gauge load cells are the most commonly used type.


  • Dual Tank Level Controller
  • Bag Filling Machine
  • Tank / Silo / Hopper
  • Food Packaging

Light Sensor

The light sensor is a passive devices that convert this “light energy” whether visible or in the infra-red parts of the spectrum into an electrical signal output. Light sensors are more commonly known as “Photoelectric Devices” or “Photo Sensors” because the convert light energy (photons) into electricity (electrons).


Despite the different types of light sensors, it can still be used in a variety of applications as seen below:

  • Consumer electronics
  • Automobiles
  • Agricultural Usages
  • Security applications

Color Sensor

A colour sensor is a type of "photoelectric sensor" which emits light from a transmitter, and then detects the light reflected back from the detection object with a receiver.
A colour sensor can detect the received light intensity for red, blue and green respectively, making it possible to determine the colour of the target object.

Touch Sensor

A touch sensor is an electronic sensor used in detecting and recording physical touch. Also known as tactile sensors, it’s a small, simple, low-cost sensor made to replace old mechanical switches we seen in the past.


  • Gaming controllers 
  • Home entertainment 
  • Home appliances 
  • Cellular handsets 
  • Portable media devices

Tilt Sensor

Tilt sensors are devices that produce an electrical signal that varies with an angular movement. These sensors are used to measure slope and tilt within a limited range of motion. Sometimes, the tilt sensors are referred to as inclinometers because the sensors just generate a signal but inclinometers generate both readout and a signal.


  • Cameras
  • Video Cameras
  • Aircraft Flight Controls
  • Construction Equipment
  • Robotic Technology
  • Automobile Air Bags
  • Videos Game Controllers
  • Studying Human Movement
  • Thermostats
  • Automobile Security Systems

PIR Motion Detector & Vibration Sensor>>

PIR Motion Detector Sensor

PIR sensor detects a human being moving around within approximately 10m from the sensor. This is an average value, as the actual detection range is between 5m and 12m.PIR are fundamentally made of a pyro electric sensor, which can detect levels of infrared radiation. For numerous essential projects or items that need to discover when an individual has left or entered the area. PIR sensors are incredible, they are flat control and minimal effort, have a wide lens range, and are simple to interface with.

Advantages of PIR Sensors

  • Small in size
  • Wide lens range
  • Easy to interface
  • Inexpensive
  • Low-power
  • Easy to use
  • Do not wear out

Areas of Applications of PIR Sensors  

  • All outdoor Lights
  • Lift Lobby
  • Multi Apartment Complexes
  • Common staircases
  • For Basement or Covered Parking Area
  • Shopping Malls
  • For garden lights

Vibration Sensor

The vibration sensor is also called a piezoelectric sensor. These sensors are flexible devices which are used for measuring various processes. This sensor uses the piezoelectric effects while measuring the changes within acceleration, pressure, temperature, force otherwise strain by changing to an electrical charge


  • The applications of vibration sensors include different industries for measuring the vibration. The exclusive industrial characteristics will decide sensor characteristics.
  • For instance, this sensor is used in industries like wind power and mining for slow rotation of turbines with 1 Hz or less frequency response.
  • In disparity, the industries like gas and oil need high frequency ranges from 10 Hz to 10 kHz uses these sensors to handle with the speed rotation of gears and turbines.
  • The industries which use the vibration sensor mainly include food & beverage, mining, metalworking, gas & oil, paper, wind power, power generation, etc.

Metal detector, Water Flow & Heartbeat Sensor>>

Metal detector Sensor

Metal detector is a device that can detect metal, the basics can make a sound when it is near some metal. Metal detectors work on the principle of transmitting a magnetic field and analysing a return signal from the target and environment.

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Water Flow Sensor

Water flow sensors are installed at the water source or pipes to measure the rate of flow of water and calculate the amount of water flowed through the pipe. Rate of flow of water is measured as liters per hour or cubic meters. Water flow sensor consists of a copper body, a water rotor, and a hall-effect sensor. When water flows through the rotor, rotor rolls, its speed changes with different rate of flow.

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Heartbeat Sensor

Heart beat sensor is designed to give digital output of heat beat when a finger is placed on it. When the heart beat detector is working, the beat LED flashes in unison with each heart beat. This digital output can be connected to microcontroller directly to measure the Beats Per Minute (BPM) rate. It works on the principle of light modulation by blood flow through finger at each pulse.


  • Digital Heart Rate monitor 
  • Patient Monitoring System 
  • Bio-Feedback control of robotics and applications

Level Sensor

A level sensor is a device that is designed to monitor, maintain, and measure liquid (and sometimes solid) levels. Once the liquid level is detected, the sensor converts the perceived data into an electric signal. Level sensors are used primarily in the manufacturing and automotive industries, but they can be found in many household appliances as well, such as ice makers in refrigerators


  • They are commonly used in applications like vaporous, Moist, and dusty environments. 
  • They are also used in systems in which temperatures differ.

Smoke, Fog, Gas, Ethanol & Alcohol Sensor Humidity, Soil Moisture & Rain Sensor

Gas Sensor

The chemical sensor device which comprises a transducer and active layer to convert chemical information into any other form of electronic signal such as frequency change, voltage or current change is known as gas sensor.

Applications of Gas Sensors

  • Used in industries to monitor the concentration of the toxic gases.
  • Used in households to detect an emergency incidents.
  • Used at oil rig locations to monitor the concentration of the gases those are released.
  • Used at hotels to avoid customers from smoking.
  • Used in air quality check at offices.
  • Used in air conditioners to monitor the CO2 levels.
  • Used in detecting fire.
  • Used to check concentration of gases in mines.
  • Breath analyzer.

Smoke Sensor

A smoke detector is a device that senses smoke, typically as an indicator of fire

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Alcohol Sensor

An alcohol sensor detects the attentiveness of alcohol gas in the air and an analog voltage is an output reading. The sensor can activate at temperatures ranging from -10 to 50° C with a power supply is less than 150 Ma to 5V. The sensing range is from 0.04 mg/L to 4 mg/L, which is suitable for breathalyzers

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Soil Moisture Sensor

The soil moisture sensor is one kind of sensor used to gauge the volumetric content of water within the soil. As the straight gravimetric dimension of soil moisture needs eliminating, drying, as well as sample weighting. These sensors measure the volumetric water content not directly with the help of some other rules of soil like dielectric constant, electrical resistance, otherwise interaction with neutrons, and replacement of the moisture content.

Soil Moisture Sensor Applications

  • Agriculture
  • Landscape irrigation
  • Research
  • Simple sensors for gardeners

Rain Sensor

A rain sensor is one kind of switching device which is used to detect the rainfall. It works like a switch and the working principle of this sensor is, whenever there is rain, the switch will be normally closed


  • This sensor is used as a water preservation device and this is connected to the irrigation system to shut down the system in the event of rainfall.
  • This sensor is used to guard the internal parts of an automobile against the rainfall as well as to support the regular windscreen wiper’s mode.
  • This sensor is used in specialized satellite communications aerials for activating a rain blower over the opening of the aerial feed, to get rid of water droplets from the mylar wrap to keep pressurized as well as dry air within the waveguides

Humidity Sensor

A humidity sensor is an electronic device that measures the humidity in its environment and converts its findings into a corresponding electrical signal.Relative humidity is calculated by comparing the live humidity reading at a given temperature to the maximum amount of humidity for air at the same temperature.


  • Industrial process control systems. Storage and warehouses
  • Climate control for green houses
  • Meteorological applications
  • Office automation, room comfort control
  • Automotive cabin air control
  • Home appliances, Air conditioners
  • Food processing
  • Medical applications
  • Chicken Coops, Pig Barns

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low-cost sensors