Sensor which converts measured variables for analysable signals with the help of an external energy source. With passive sensors, electrical such as resistance, capacitance and inductance are modified in proportion to the measured variable to be recorded, i.e. an indirect measuring method is used. There is no signal processing, because no electrical is forthcoming until a connection is establish to an external auxiliary circuit. Examples: piezoresistivesensor, position measurement by potentiometer.
Opposite: active sensor