measure the time between two transitions: ttr
it's the time it takes to go 60 electrical degrees (or 1/6 electrical period)
electrical frequency = (1/6) / ttr
multiply by 2xpi to get rd/s
multiply by number of pole pairs (P) to get mechanical speed
multiply electrical frequency by 60xP to get RPM
please correct me for folllwing example if it is wrong:
For 4 pole motor,
If i got one of 3 hall sensor output with frequency of 125 Hz, then speed will be:
2 pulse = 1 mechanical revolution.
So, for 125 Hz (125 pulse per second), speed = (125/2) revolution per second.
Which will give (62.5 * 60) = 3750 RPM
Thanks a lot!
If the system has to be closed loop then , does above method to decide the motor present speed is accurate?
Or what would be any other more accurate approach?
Yes, you could have closed loop speed control with such a feedback. Just make sure your controller bandwidth isn't too much in conflict with you minimum operating speed (your speed estimation isn't "refreshed" as often at low speeds).