# Power Factor Meter-how to detect leading or lagging PF

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#### pete

##### Member level 2 power factor pic

Hi! Am trying to design a PIC-based power factor meter. My problem is how to detect which wave comes first. Say, I have two sine waves,one for voltage and the other for current. I can convert these 2 waves into pulses. How would the PIC detects which one of the two pulses comes first. I can get the difference in times to get the power factor but how would I know if the current leads the voltage or the other way around? That is, how would I know if the power factor is leading or lagging without knowing in advance the type of load.
Any help would be much appreciated.

Thanks a lot...

#### Davood Amerion power factor formula

it is simple,
in your program first read voltage sample, then current sample and measure time diffrence .
if (in 50Hz & 20mS period) diffrence was smaller than 5mS current lagged,
and if diffrence was 15mS-20mS first calculate (timeDiff - 20ms)
then you get what you want! #### pete

##### Member level 2 pic based power factor meter

"it is simple,
in your program first read voltage sample, then current sample and measure time diffrence .
if (in 50Hz & 20mS period) diffrence was smaller than 5mS current lagged,
and if diffrence was 15mS-20mS first calculate (timeDiff - 20ms)
then you get what you want!"

Can I generalized it?

For 50hz, sample first the voltage. Then let D be the time difference of voltage time minus current time. If D is less than or equal to 5ms, then current is lagging the voltage. If D is less than or equal to 15ms or if D is less than 20ms, then current is leading the voltage by 20ms minus D. I hope this is correct formula.

#### glenjoy

##### Banned lagging pf

The formula is only based on assuptions of data, chances are the data that will be gathered could be inconsistent and unreliable.

#### Davood Amerion pic power factor

For 50hz, sample first the voltage. Then let D be the time difference of voltage time minus current time. If D is less than or equal to 5ms, then current is lagging the voltage. If D is less than or equal to 15ms ...
note:
diffrence cannot be between 5...15mS! #### pete

##### Member level 2 lagging power factor formula

Davood Amerion said:
For 50hz, sample first the voltage. Then let D be the time difference of voltage time minus current time. If D is less than or equal to 5ms, then current is lagging the voltage. If D is less than or equal to 15ms ...
note:
diffrence cannot be between 5...15mS! You are correct. Putting in formula what I said:
If Δ is Vtime - Itime and f=50hz, then

Current lagging: Δ<=5ms

#### lats

##### Full Member level 4 pf lagging

hi m also trying to build a power factor meter , i have designed the part of measuring pf but how to check whether its lagging or leading. i read the above replies but the doubt in my mind is why cannot the diffrence be between 5...15mS. m conceptually weak in this .please explain me in more detail.

#### pete

##### Member level 2 microcontroller power factor meter

Try to plot a single sine wave with the horizontal axis as time. Calibrate your time axis in milliseconds. One cycle is 1/50hz sec. Draw this in a clear transparent paper. One for the voltage colored blue and the other is for the current colored red. Try to superimpose the two transparencies.With the voltage stationary, move the current wave left to right a little. Then you will understand it.

#### Dicken

##### Newbie level 1 pic power factor measurement

Hi, i'm also do this project to.can you give me your zero crossing detector circuit?

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