These transducers are shaft industrial encoders which give absolute measurements on more than one revolution of their shaft.
The encoders have a mechanic gear train which transmits the movement of its master disc to a series of slave discs for shaft revolution counting.
An electronic circuit cancels any mechanic backlash of the gear train, thus yielding a detection's.
They are mechanically strong and properly engineered in their electronics, optical and mechanic parts, being thus able to withstand heavy duty conditions.