how we can find out the speed of fan without using any
measuring instrument

Answer Posted / mr.engineer

If it has a direct coupling with the motor .Use this formula
n=(120*frequency)/(2*number of Poles.)

Number of poles:You can get it from name motor name plate .
Frequency:50Hz or 60hz depends on your system.

(Or you can see Motor Speed and fan speed will be same as
motor speed)

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