How Speed Sensors Work

Conventional Sensors
This is based on the principle of electromagnetic induction and uses a rotating gear tooth or phonic wheel to cut a magnetic path, inducing an alternating output voltage. The frequency of the output is proportional to the rotating speed.

The conventional coil is simple but requires a large number of turns to generate a reasonable output voltage.

The output of a conventional speed probe versus a Weston Aerospace transformer speed probe

Weston’s Patented Transformer Probe
The primary circuit operates at low voltage/high current, with a step up transformer on the output to give the desired output voltage.

This gives several benefits:
	Robust sensor for use in hotter / high vibration environments
	Can be fitted in smaller and unusual shaped locations
	Easy to set a given output voltage
	Higher output voltage at low speed