Passive sensor: Generates its own electrical signal from the measured physical quantity.
Example: A piezoelectric sensor is a passive sensor.
Reason: A piezoelectric sensor generates an electrical charge or voltage directly when mechanical pressure, force, or vibration is applied to it. It does not require an external power supply to generate this signal.
A piezoelectric sensor used to detect vibration in a machine.
Therefore, a piezoelectric sensor is classified as a passive transducer because it converts mechanical energy into electrical energy directly.
Active sensor: Requires external excitation or power to operate, such as an RTD (which requires a measuring current).