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Power Factor Measurement

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New Member
Can somebody provide me with circuit for calculating power factor using standard components ?

I tried to build circuit, but could not measure pf correctly. First the output of voltage and a current transformer were amplified and fed to zero crossing detector ( using LM339).

These zero crossing TTL outputs of LM339 were give to microcontroller and time difference calculated using s/w.

However the circuit behaves erratically for inductive loads. My querries are

1. Is filtering of o/ps of voltage & current transformers arre needed ?
2. If yes , the is there an IC which can do this or shall I design my own low pass filter especially to do with inductive loads which produce high noise on the line and I found that the waveforms are distored



Well-Known Member
Yes you need filters. There is a lot of noise on power supply lines.

I suggest either a low pass or band pass. The filters could either be LC or active.

There have been enquiries in the past in this forum about filters. So I suggest you do a search for eithe "filters" or "active filters"

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