Angle sensors eliminate dynamic errors at high axial speeds

June 23, 2014 // By Graham Prophet
ams' latest magnetic position sensors claim to offer the best-available accuracy at high rotation speeds; AS5047D, AS5147 and AS5247 have a technology ams terms DAEC compensation technology to reduce dynamic angle error to almost zero

These magnetic position sensors are capable of producing extremely accurate angle measurements of rotors spinning at high speed. The “47 series” position sensors include the AS5047D, AS5147 and AS5247 with DAEC (Dynamic Angle Error Compensation), that ams developed to eliminate measurement error attributable to propagation delay.

Use the AS5047D for industrial applications including robots and encoder modules.

AS5147 is an AEC-Q100 qualified part for automotive applications such as electronic power steering and pumps.

The dual-die AS5247 (also AEC-Q100 qualified) is suited for automotive applications requiring the highest level of functional safety compliance.

All three parts are specified with a maximum ±0.17° angle error (excluding integral non-linearity).

This precision measurement performance is the result of implementing the algorithm which performs error compensation internally and responds automatically to changes in the speed of rotation. Traditional magnetic rotary position sensor ICs suffer from a propagation delay (typically 100-200 µsec) as they convert raw measurements of magnetic field strength at their embedded magnetic elements into digital angle measurements. During this delay, a spinning rotor's angular displacement changes, so that its actual position when the digital output leaves the sensor differs from its measured position.

The resulting error increases in a linear fashion with increases in the speed of rotation: for a propagation delay of 100 µsec, at 1,000rpm the dynamic angle error is 1.2° and at 10,000rpm it is 12°.

DAEC almost completely eliminates this source of error, dynamically compensating every measurement sample for the speed of rotation at the time the sample is captured. The 47 series sensors provide angle measurements accurate to ±0.08° at 7,000rpm, to ±0.14° at 12,000rpm and to ±0.17° at 14,500rpm.

With its extreme accuracy, the ams 47 Series is ideally suited to all motor control and angle measurement applications. In high-speed brushless DC (BLDC) motors and permanent magnet synchronous motors (PMSM) the sensor’s high accuracy enables better execution of the commutation scheme, resulting in higher torque and efficiency,