On Axis and Off Axis Magnetic Encoders: What’s the Difference?

All magnetic encoders have the benefits of working well in harsh environments and being easy to install. There are two fundamental types of rotary magnetic encoders on the market, on axis and off axis. Each has different physical and performance characteristics.

On Axis
As the names suggest, the on axis design has the sensor located directly over the center line of the shaft.

On Axis encoders

  • Sensor and magnet must be aligned with the center line of the rotating shaft.
  • Button-shaped rare earth magnet mounted directly on the end the shaft.
  • Can offer absolute position information and/or quadrature signals

Off Axis
The off axis design has the sensor sitting off to the side of the shaft with the magnetic target in the form of a ring.

Off Axis encoders   (Timken M15 shown)

  • Do not block access to the end of the shaft.
  • Shorter installed height; more tolerant of sensor and magnet position at installation.
  • Higher accuracy and less latency than on axis designs.
  • One chip works with a wide range of pole sizes and diameters.

For a more in-depth comparison see my paper on the same subject.

The charts below offer additional guidelines that may make your choice clearer.

If you still have questions and would like to discuss whether an off axis or an on axis encoder is the right choice for your application, call me at 603.358.4760 or send me at email at [email protected].