Velocity sensors or velocimeters measure absolute casing vibration and – in combination with a trigger measurement – magnitude and phase.

Velocity sensors are mounted to the measured object. They usually have a rugged design, are highly sensitive at low frequencies, are simple to mount and don’t need an external power supply.

Measurement principle:

The magnet of the velocity sensor is suspended on a membrane (spring) which moves through a coil of wire. Due to the vibration, the coil of wire moves through the magnetic field of the permanent magnet and generates (induces) a voltage signal which is proportional to the vibration (velocity).

The measurement direction is important: Some types are mounted vertically, others horizontally!