SLVSCP6H July 2014 – June 2020 DRV10983
The motor operation speed is automatically updated in register MotorSpeed1 and MotorSpeed2 while the motor is spinning. MotorSpeed1 contains the 8 most significant bits and MotorSpeed2 contains the 8 least significant bits. The value is determined by the period for calculated BEMF zero crossings on phase U. The electrical speed of the motor is denoted as Velocity (Hz) and is calculated as shown in Equation 8.
As an example consider the following:
MotorSpeed1 = 0x01;
MotorSpeed2 = 0xFF;
Velocity = 512 (0x01FF) / 10 = 51 Hz
For a 4-pole motor, this translates to:
The electrical speed of the motor (Hz) readback from MotorSpeed1 and MotorSpeed2 is not accurate and has up to 6% error. For accurate results, it is recommended to read the Motor electrical period (see Motor Electrical Period Readback) and then calculate the electrical speed of the motor (Hz) manually by calculating the inverse of Motor electrical period or measure the frequency of the FG signal output (see FG Output Frequency).