Hello,
I am currently working on an off-axis rotor angle sensing project for a motor control application. The measured angle will be used as the position feedback for FOC.
My main requirements are:
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Off-axis / side-shaft magnetic angle measurement
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Target angular accuracy: 0.1°
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Maximum motor speed: approximately 3000 rpm
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Operation close to the motor, where stray magnetic fields from the stator and phase currents may be present
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The motor temperature may increase during long-term operation
According to the MA600A datasheet, the device supports side-shaft mounting and can achieve <0.1° INL after user calibration with the 32-point correction table, which seems suitable for my accuracy target.
However, I still have some concerns:
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Does the <0.1° INL after user calibration represent the residual error of the complete sensor + magnet + mounting configuration at the calibration condition, or only the intrinsic error of the MA600A?
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If the system is calibrated at room temperature, how much angular accuracy can be expected when the motor and sensor temperature increase during operation? Is it realistic to maintain approximately 0.1° total angle accuracy over temperature?
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Does the MA600A have any built-in immunity or rejection mechanism against external / stray magnetic fields, especially magnetic fields generated by a BLDC/PMSM stator and phase currents? If not, what design recommendations would you suggest to minimize this error
Would you consider the MA600A suitable for this application if the final system requirement is approximately 0.1° angular accuracy, or would you recommend another MPS magnetic angle sensor for this type of off-axis motor application?
Thank you for your support.
Best regards
Hello @le.thanh.dat09052,
Does the <0.1° INL after user calibration represent the residual error of the complete sensor + magnet + mounting configuration at the calibration condition, or only the intrinsic error of the MA600A?
The MA600A can indeed achieve less than <0.1 deg of INL after user calibration, this calibration corrects the error caused by the full setup (sensor + magnet + configuration) but it is important to note that not all setups can achieve this level of error.
As a general rule, you can follow these steps:
- Measure initial INL: ~30-60 deg (since no BCT or CORR is configured).
- Set BCT: <10 deg after configuration (see Bias Current Trimming Settings section on the datasheet). You can obtain an initial BCT estimation on our Simulation Tool and then adjust it manually to obtain the optimal value.
- Calibrate: <1 deg afterwards(you can perform this calibration using the Evaluation App).
If steps 1 and 2 present a higher INL error, then the calibration will most likely not accomplish the desired 0.1 deg of INL.
If the system is calibrated at room temperature, how much angular accuracy can be expected when the motor and sensor temperature increase during operation? Is it realistic to maintain approximately 0.1° total angle accuracy over temperature?
This value is actually characterized on the General Characteristics table on the datasheet:
Does the MA600A have any built-in immunity or rejection mechanism against external / stray magnetic fields, especially magnetic fields generated by a BLDC/PMSM stator and phase currents? If not, what design recommendations would you suggest to minimize this error
It does not, we also offer differential sensors for this purpose, but they cannot be placed on side-shaft so they are not valid for your setup.
There are some methods to reduce the stray-field induced error, but they are highly setup dependant:
- Distance: Move the sensor as far as possible from the stray field source.
- Sensor orientation: The MA600A is sensitive to Bx and By so any stray fields oriented on Bz will not affect the sensor performance.
- Shielding: Surrounding the magnet and sensor with ferromagnetic material. It usually recommended only as a last resource due to it causing a distortion on the target field.
