Most sensors are either electrical or electronic devices however there are other types in existence. We will focus on electronic sensors. These types of sensors are electronic transducer devices that sense or recognize signals and are able to analyze and measure them. The signals can be in a wide variety of forms such as temperature, force, strain, stress, voltage, light, impedance, etc. Sensors are used in a wide spectrum of industries and applications such as medical, electrical, physics, nuclear research, defense, seismology, acoustics, measurement devices, etc.
Sensors come in two types, direct and indirect. Items such as analog devices, pointers with graduated scales and digital interfaces, etc. are integrated to a sensor so that humans can understand their readings. A good sensor should be sensitive to the property that is being measured and it should be insensitive to all other properties. In addition, a good sensor should not influence the measured property in any way.
Since signals consist of a transfer of energy, sensors can be classified according to the type of energy transfer that they detect. The type of sensor used depends on the application. Some types of sensors are:
- Resistance/current/voltage/power sensors are used to measure electrical resistance, current, voltage and power respectively. Examples are ohmmeter, ammeter, voltmeter and watt-hour meters.
- Magnetic sensors: These are used to measure the magnetic flux. Examples of these include compasses and magnetometers.
- Pressure sensors: These sensors are used to measure the pressure in air and fluids. Examples of these are barometer, pressure gage and variometer.
- Motion and proximity sensors: These are used to measure motion. Common examples of these sensors are speedometer, radar guns, and tachometer, etc.
- Light sensors: These sensors are used to measure the intensity of light like photometers.
- Chemical sensors are used to measure the presence of specific chemicals or classes of chemicals. Examples of these sensors include oxygen sensors which are also known as lambda sensors, ion-selective electrodes, pH glass electrodes, and redox electrodes.
- Other types of sensors are used to measure things such as distance, smell and chemical in medical applications, heat etc.