Author Topic: Is the reading of a 'moving iron' type analog ammeter skewed by power factor?  (Read 526 times)

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Offline thomastheoTopic starter

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I had a discussion about this today, and couldn't answer adequately, so perhaps one of you can help. Say you are measuring AC current into an inductive load with a poor power factor, and are using an old-fashioned analog ammeter with a moving iron mechanism, what will the reading show?
 

Offline bdunham7

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In the case of an inductive load, where the power factor is solely due to phase shift and the current is still sinusoidal, the meter should read the actual current normally.  The ammeter only knows what it sees across its shunt, it can't know about the phase difference between the current and the voltage across the load.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline TimFox

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A "moving iron" or "moving vane" meter responds to the average value, i.e. mean of the absolute value of the current through the winding.  The harmonic content of the current waveform will affect the rms value indicated, but the meter does not see the voltage across the load.  A "moving coil" or "d'Arsonval" meter responds to the mean of the current or DC value, so it cannot measure AC directly, only through a rectifier of some kind.
 


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