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Gearless multi-turn sensors with digital interfaces

Novotechnik (Germany) has developed the GMR sensor technology and offers the multi-turn sensors of its RSM 2800 series equipped with digital interfaces. A version with CANopen interface will be available as well.

Novotechnik offers the multi-turn sensors of its RSM 2800 series equipped with digital interfaces (Photo: Novotechnik)

MULTI-TURN SENSORS THAT UTILIZE THE GMR EFFECT (Giant Magnetoresistance) yield absolute positional values, do not require any type of reference signals, and need neither power supply nor buffer battery for rotational sensing. They are used in so-called True Power On-Systems for a variety of industrial applications.

The measuring range of the released rotary sensors is 14 or 16 revolutions; measurements are output as SPI or SSI signals. These sensors, with their diameter of only 28 mm, are designed for total resolutions in the range of 16 to 18 bits (14 bits for angular sensing, and 1 to 4 bits for revolution counts). Their linearity deviations lie at +/-0,036 % over the entire measuring range. By combining single-turn angle detection and a separate turn detection, these sensors are able to measure angles across multiple turns. The sensors can detect turns in unpowered state and store turns non-volatile. They work internally magnetic and thereby contact-free. Electrical connection is made via a shielded cable, which is potted into the housing. The sensors of this series are designed to comply with protection requirements of up to IP67 and are therefore protected against dust and temporary submersion. The shaft design permits take-up with angular-indexing by a customer-supplied counterpart. Typical applications include mobile machinery, actuators, or hydraulic lifts, as well as robotics. Generally, they are utilized as alternatives to multi-turn potentiometers and encoders. The CANopen version is expected to be available in the middle of this year.

The sensors of this series are the first rotation counters to be based on the company's patented Novoturn technology, which is built on an enhanced giant magnetic resistance effect. Magnetoresistance is a phenomenon in quantum mechanics that occurs in thin film structures when two ferromagnetic layers are separated by a thin non-magnetic film. It is a technology used in hard disk drives. When the two magnetic layers are parallel, resistance drops to a minimal value. As the magnetic layers are turned so they are no longer in parallel alignment, electrical resistance increases. This increase can be used to measure absolute position values, e.g. full rotations.

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