Hi guys,
just a quick question about the power factor using emonlib.
I know using emonlib that we cannot tell if the load is leading or lagging or if the load is more inductive than capactive. In such as case however, the PF will always read as a positive number however?
I was just looking at the results from a Fluke energy logger and it can determine if the load is indeed leading or lagging and hence fires out negative values or positive PF values depending on the load.
The PF reading from Emonlib will always be positive wont it?
I am using a mega with a CT and VT and emonlib.
Thanks guys
Regards
No, but not for the same reason!
EmonLib calculates power factor according to the definition, i.e. the ratio of real power to apparent power. Apparent power must always be positive, because rms values are always positive. If real power happens to be negative (either you’re exporting or the phase of your c.t. is wrong), then the value will be negative.
The only way to detect leading or lagging is to compare against a quadrature voltage, which you can do (but we don’t) by storing the voltage samples for ¼ cycle so that the voltage phasor is aligned on the imaginary axis, and then running the same calculation as real power on the delayed samples. That will give you the imaginary (reactive) power, signed just like real power is, but indicating leading or lagging.
Then of course by looking at the signs of both real and imaginary powers, you can see which of the 4 quadrants your load is in.
It can’t be both at the same time - overall, it’s got to be one or the other - or neither if it’s purely resistive. 
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Hi Robert,
just after I typed the question I remember a post you replied to stating that the power factor will be correct but just not the sign. Come to think of it, that may have been a question or part of one i asked here in the past. The PF reading is still very useful the way it is calculated by emonlib, just not the sign.
Thanks again for replying. I appreciate your input, as always