Circuit diagram is shown Here input of FAN is connected to current sensor through a regulator My question is..
- Is it ok to measure AC current through this sensing IC(ACS712) When fan speed changes ?
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Your picture shows ACS712, so I will stick to it as ACS741 is of non-existence (or, did you mean ACS714?)
ACS712 allows of measuring current from +/- 5A (part x05B) to +/-30A (part x30A).
ACS712 provides economical and precise solutions for AC or DC current sensing
So, yes, you can use it to measure AC current when fan speed changes, providing your fan doesn't draw more than 5A (for part x05B).