A range of non-contact multi-turn angle sensors available from Variohm EuroSensor are designed to offer improved resolution, better repeatability and longer life than contact based potentiometer devices.

The RSM 2800 from Novotechnik is a 28mm diameter sensor providing a 12-bit absolute position resolution over a selectable range of up to 15 turns (5400 degrees). With a choice of voltage or current output as standard, a digital version with 0.1 degree resolution is also available.

The sensor uses giant magneto resistance, a technology used in hard disk drives, where thin film deposits of sandwiched magnetic and non-magnetic layers can be combined with sensors on ‘spiral arms’ to return an absolute position value over a single rotation.

To provide an absolute position value over a multi-turn range, a 360 degree Hall effect sensor is included with multiple spiral arms that correspond to each rotation. Furthermore, the position is available with true power-on sensing for first time operation on start up with no calibration required.

See http://www.variohm.com