A sensor is a device that responds to an input physical property (stimulus) and converts it into an electrical signal, compatible with electronic circuits. In this way, all sensors are energy converters.
A sensor does not function all by itself. It is always part of a data acquisition system in a feedback mechanism that may incorporate many other detectors, signal conditioners, signal processors, memory devices, data recorders, and actuators.
Sensors are of two kinds: passive and active. A passive sensor generates an electric signal in response to an external stimulus without the need for an additional energy source. The active sensors, on the other hand, require external power for their operation and to produce the output signal.
Sensors fundamentally transform the physical world into digital insights. They range from very simple to complex, depending on their purpose. This post explores some of the common types of sensors and their applications.
Thermal sensors
Temperature or thermal sensors are everywhere. They are in household ovens, refrigerators, and thermostats all rely on temperature maintenance and control to function correctly. They are used to measure the temperature of a medium.
- Thermometer – measures absolute temperature.
- Thermocouple gauge– measures temperature by its effect on two dissimilar metals. It directly converts thermal energy into electrical energy.
- Calorimeter – measures the heat of chemical reactions (physical changes) and heat capacity.
- Bolometer – measures the power of incident electromagnetic radiation.
- Bimetallic strip – converts a temperature change into mechanical displacement.
- Infrared thermometer – infers temperature from a portion of the thermal radiation emitted by an object.
- Microwave radiometer – measures microwaves.
- Pyrometer – measures the temperature of distant objects.
Mechanical sensors
Mechanical sensors are devices used to monitor activities of the body, including pressure, position, velocity, force, strain (body deformation), acceleration, and body temperature.
- Pressure sensor – measures the pressure.
- Barometer – determines the level of atmospheric pressure. The aneroid barometer is another type of barometer that senses atmospheric pressure changes by the expansion or compression of an aneroid capsule.
- Altimeter – measures the altitude of an object from a fixed level.
- Gas flow sensor – measures direction, velocity, and flow of gas.
- Liquid flow sensor – measures liquid flow rate.
- Accelerometer – measures acceleration, vibration and shock.
Electrical sensors
- Ohmmeter – measures resistance
- Galvanometer – measures current
- Ammeter – measures the strength of electric current
- Voltmeter – is a specific type of ammeter used for sensing an electrical current.
- Watt-hour meter – measures the amount of electrical energy supplied to and used by a residence or business.
Chemical sensors
Chemical sensors are the devices to detect the presence of certain classes of chemicals and quantify the amount and type of chemical detected. They have numerous medical, industrial, and commercial applications such as environmental, quality control, food processing, and medical diagnosis.
- Oxygen sensor – measures the percentage of oxygen in a gas or liquid.
- Carbon dioxide detector – detects the presence of CO2.
- Breathalyzer – estimates blood alcohol content (BAC) from a breath sample.
- Chemical field-effect transistor – measures chemical concentrations in solution.
- Electrochemical gas sensor – measures the concentration of a target gas by oxidizing and measuring the resulting current.
- Holographic sensor – detects specific molecules or metabolites.
- Ion-selective electrode – converts the activity of a specific ion dissolved in a solution into an electrical potential.
Biosensors
Biosensors are analytical tools for analyzing bio-material samples to understand their bio-composition, structure, and function by converting a biological response into an electrical signal. They are used in the clinic, diagnostic, medical applications, process control, bioreactors, quality control, agriculture and veterinary medicine, bacterial and viral diagnostic, drag production, industrial wastewater, mining, and military defense industry.
- Potentiometric – measures variations in open circuit potential.
- Immunosensors – measures immunochemical reaction.
- Amperometric – measures currents due to oxidation or reduction of electroactive species.
- Magnetic biosensors – measure changes in magnetic properties of magnetically induced effects.
- Thermometric biosensors – measure the temperature change of the solution containing the analyte caused by these enzymatic reactions.
- Acoustic (piezoelectric biosensors) – measure the change in the physical properties of an acoustic wave.
- Optical biosensors – measure the interaction of a visual field with a biorecognition sensing element.
- Colorimetric – measures changes in light adsorption
- Photometric – measures light intensity.
Acoustic sensors
Acoustic sensors measure different frequencies of sound waves created by compression and expansion of solids, liquids, or gases.
- Seismometers – measures seismic waves.
- Acoustic wave sensors – measure the wave velocity in the air or an environment to detect the chemical species present.
- Microphone – measures airwaves in the audible range.
- Hydrophone – measures liquid waves.
- Geophone – converts ground movement (velocity) into voltage.
Optical sensors
Optical sensors convert light rays into an electronic signal. They measure a physical quantity of light and, depending on the type of sensor, then translate it into a readable form by an integrated measuring device. These sensors are commonly used for quality and process control, medico technologies, metrology, imaging, remote sensing, etc.
- Light sensors (photodetectors) – detects light and electromagnetic energy.
- Photocells (photoresistor) – a variable resistor affected by intensity changes in ambient light.
- Infrared sensor – detects infrared radiation.
- Photoconductive – measures the resistance by converting a change of incident light into a change of resistance.
- Photovoltaic – converts an amount of incident light into an output voltage.
- Photodiodes – converts an amount of incident light into an output current.
Other
- Motion – detects motion
- Speedometer – measures speed
- Geiger counter – detects atomic radiation
- Proximity – detects the presence of objects.
- Dynamometer – measures force, power, or torque.
