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Firmware Stable

Motor sensors

AC electric motors are manufactured with various rotor position sensor types. The controller supports various interface types and paying attention to the matching selection is necessary.

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  • This common section covers the rotor position sensors only. For information about interfacing motor temperature sensor, please refer to the specific controller's electrical specification and guidelines.
  • All siliXcon controllers feature sophisticated synchronous sampling technology for motor sensor signals. This technique substantially reduces electromagnetic interference concerns when routing sensor signals near power phase wires.

Supported rotor position sensors (according to their interface) are:

Analog sin-cos interface sensors offer versatile position sensing across various technologies (magnetic, optical, or inductive). Sin-Cos signal is composed of two analog signals of sinusoidal shape. Signals are phase-shifted by a quarter of the period and one period of sine (or cosine) signal corresponds to one mechanical turn of the motor (see pic. below). This type of signal is usually produced by a sensor consisting of a cylindrical permanent magnet glued to the rotor and a sensor chip located on the stator at a defined distance from the cylindrical magnet.

SinCos signal

Sin-Cos motor sensor is supported by "a" Motor sensor assembly variant.

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BLDC driver algorithm does not support Sin-Cos sensor

ProsCons
Absolute and continuous position sensing.Typically sense mechanical revolutions. Angle multiplication error could occur when using a motor with many pole pairs.
Suitable for position servo drives.Analog interface – could be sensitive to electrical interference.
Needs output offset calibration (can be done automatically by the controller).
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Selection guidelines​

Based on our experience, the critical consideration when selecting these sensors is the matching of pole pair counts between the sensor and rotor. Many sin-cos sensors detect mechanical revolution rather than electrical angle, requiring the controller to perform angle multiplication for proper motor commutation. For sensors utilizing a single sensing element (such as in-shaft magnet designs), we've found that the practical multiplication limit is typically five times before accuracy degradation becomes problematic. Although a firmware compensation table reduces the symptoms, the inacurracies tend to drift with time (temperature, age, ...). This limitation should be carefully evaluated when selecting sin-cos sensors for applications with high pole pair counts to ensure reliable position feedback and optimal motor performance.

Example parts​

When interfacing with sin-cos analog output sensors, output voltage range is the primary consideration. Optimal performance is achieved with sensors featuring ratiometric output centered at mid-supply voltage (2.5V when using the 5V provided by our controller). For signal integrity, the amplitude swing should remain within 90% of both upper and lower voltage margins, avoiding rail saturation that could introduce non-linearities. The following in-shaft magnet sensors with sin-cos output have been tested and proven reliable in field applications:

  • RLS AM256 or AM4096 chip
  • RLS RMB29 module

Installation Best Practices​

To maintain reliable sensor performance, especially during short-term motor current overload conditions, implement these protective measures against coil induction interference:

  • Install decoupling capacitors on the supply voltage in close proximity to the sensors themselves.
  • For in-shaft magnet sensors, ensure precise magnet alignment, as any mechanical misalignment or temperature instability will be amplified through angle multiplication, potentially introducing significant control errors.
  • For maximum resilience, position magnets at sufficient distance from motor windings to minimize electromagnetic interference with the sensing elements.