Passive vs. Active Sensors

Passive

A physical values, $x$, changes a passive property of the device, $f(x)$. For example:

• Resistance
• Capacitance
• Inductance
• Other passive properties: mass, inertia, optical density, etc.

This then requires conversion to a voltage or current signal, $y$ (signal conditioning). Passive sensor modules can include integrated signal conditioning.

Active

A physical effect creates an output signal voltage or current, $y$, directly from a physical value, $x$. Some physics principle couples $x$ and $y$.

For example, piezoelectric material relates mechanical strain and voltage. This may require external power to function.