Contactless electrical switch for detecting positions using the Hall effect: if a current-carrying conductor is exposed to a magnetic field, a "Hall voltage" is generated in the conductor, which — duly amplified — produces an output signal (Figure H 5).
Hall effect sensors operate independently of the rate of change and also over quite large distances. Their accuracy is ±0.2% based, for example, on a measurement range of 0 to 250 mm.
Figure H 5: Hall effect sensor