Inductive Type Velocity Output Vibration Sensors such as IRD544 and IRD544M work on the principle of Electromagnetic Induction.

These sensors do not require an external supply voltage to function and are therefore also known as Self Generating type Vibration Sensors. When placed on a Vibration Surface, the Mechanical motion (Vibration) is converted to an Electrical Signal by the Sensor. The sensor does this by keeping a coil suspended between magnets. The sensor assembly tries to keep the coil stationary when there is vibration. A relative motion is generated between the magnet and the coil which induces an EMF in the coil.

This EMF is proportional to the Magnetic Flux Density (Constant for the Sensor), Length of Conductor (constant for the sensor), Sine of Angle (constant for the sensor) and Velocity (variable). This is why the sensor is called as an Inductive Type Velocity Output Vibration Sensor