MCT8316A: Motor Lock Detection

Hi Fengyu,

The term "Lock" doesn't mean the motor getting locked. We have lock mechanisms to protect the device and the motor from failures. MCT8316A monitors the speed continuously by calculating difference in time between subsequent back EMF zero crossings. This fault is to protect the motor from spinning at very high speeds. This fault gets triggered when motor speed exceeds abnormal speed threshold [LOCK_ABN_SPEED]. Another reason to have this fault is when the motor gets stuck in the first electrical cycle, device continues to commutate at frequencies above the configured abnormal speed threshold [LOCK_ABN_SPEED]. You might see the motor vibrate when this happens. To avoid such conditions, we have this fault in place. 

Loss of sync can get triggered when the motor loses synchronization due to improper selection of motor startup and open loop acceleration profiles. Abnormal speed and loss of sync might not always get triggered at the same time. The conditions for detecting both faults are different. However, when the motor vibrates and stalls, we might see both faults get triggered. 

Regards,

Vishnu

Fengyu Leng said:

. I can't understand why motor is over speed when motor Locks. Could you please tell me the principle briefly?

I think originally Motor_Lock is a flag that is set whenever the motor is not turning above a certain speed threshold in the register. But later the designer also added "abnormal motor speed" to set the same flag whenever the motor speed exceeds a threshold - to avoid run-away situation which is dangerous. Instead of using two different flags -- one for Lock and one for abnormal fast, designer conveniently combined them into just one protection flag: Lock.

Brian