Sensor

A sensor is also referred to as a transmitter or pick-up and qualitatively or quantitatively (as values) records specific (physical or chemical) properties of its environment as a technical component, whereby variables not suitable as signals are converted to signals designated for further processing.

Sensor classification based on energy usage

• Active sensor: Active sensors do not require a power source. They provide a signal in the form of an electrical voltage, charge, or current such that only changes in the measurand can be determined.
• Passive sensor: Passive sensors change an electrical parameter such as resistance, capacity, or inductivity and require a power source for this purpose. This also enables the measurement of static or quasi-static measurands and is the reason why these sensors are typically used.
• Optical sensor: Optical sensors transform non-optical variables into optical signals, which are subsequently processed further by opto-electronic devices. 

Sensors (measuring elements) differ according to their measuring principle.

Measuring principles

• Differential transformer, e.g. displacement sensor 
• Inductive sensor, e.g. valve disc positioning
• Capacitive sensor, e.g. pressure or level measurement
• Bubbler control,  e.g. level measurement in waste water plant
• Magnetic field measurement, e.g. distance measurement as proximity sensor
• Magneto-elastic measurement, e.g. torque or force measurement 
• MIF (Magnetic-Inductive Flow measurement)
• Opto-electronic sensor, e.g. light barrier
• Piezoelectric sensor, e.g. pressure, oscillation, and force measurement
• Resistive sensor, e.g. strain gauge
• Temperature sensor, e.g. PT 100
• Thermoelectric principle, e.g. temperature measurement
• Eddy current sensor, e.g. layer thickness measurement

Configured (selected) sensors

• Absolute pressure sensor, e.g. air pressure measurement
• Differential pressure sensor
• NTC thermistor (see NTC resistor), e.g. temperature measurement
• Inductive proximity sensor, e.g. non-contact displacement/position measurement
• Inductive displacement sensor, e.g. displacement/position measurement
• PTC thermistor (see PTC resistor), e.g. temperature measurement
• Level, e.g. water, fill, sound, signal, and voltage levels
• Float switch, e.g. dry running protection for submersible motor pump
• Thermocouple, e.g. temperature measurement

If the sensors are equipped with integrated measured value conditioning, they are referred to as sensor systems.