Active instrument vs Passive instrument-Difference between Active instrument and Passive instrument

This page compares active instrument vs passive instrument and mentions difference between active instrument and passive instrument. It mentions definitions and examples of active and passive instrument types.

Active instrument

active instrument

Definition: The instrument type in which quantity to be measured modulates or adapts to magnitude of external power source is known as active instrument.

Example: Petrol Tank Level Indicator
The change in petrol level moves a potentiometer arm and the output signal consists of a proportion of the external voltage source applied across the two ends of the potentiometer.
The energy in the output signal comes from the external power source. In this active instrument, primary transducer float system is merely modulating the value of the voltage from this external power source.

Passive instrument

passive instrument

Definition: The instrument type in which output entirely depends on quantity to be measured.

Example: Pressure measuring device
The pressure of the fluid is translated into a movement of a pointer against scale.
The energy expanded in moving the pointer is derived entirely from the change in pressure measured. In this passive instrument,there are no other energy inputs to the system.

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