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.
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
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].
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Myself and two of our top engineers in this field will post new topics biweekly. We hope these posts answer some of your questions and generate discussion.
Meet the Timken panel:
Robert Stiffler – Business Development Manager – The Timken Company (2010 – Present)
I manage the day-to-day business of Timken sensors and encoders. I also create and implement business strategy to drive profits and growth in industrial motion control electronics.
John Santos – Chief Engineer – Sensors – The Timken Company (2007 – Present)
John leads all aspects of engineering for Timken’s multimillion-dollar sensor business, from product design to applications and manufacturing engineering, and IP management.
Mark LaCroix – Principal Application Engineer – The Timken Company (1987-Present)
As the lead sensors applications engineer at Timken, Mark has designed and developed magnetic sensors for 28 years including sensor ASIC chips, complex magnets and magnetic patterns and magnetic encoders.
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