Callibration

Hi,

I've build the basic energy monitor - Mains AC: non-invasive 3.0 using a 9 volt AC adapter and a current sensor that outputs a voltage.

My problem is that I can't get the calibration right.

The first problem I've noticed is that the output without a consumer of power isn't floating around 0 and more something like this -3.70 9.08 -0.41 V:237.60 I:0.04.
What can i do to level this closer to 0?

Then I've connect a heater that consumes about 2000 W and calibrated this to match the output of the arduino. But when i than connect a 25 W device I get a 50 W from arduino.

What I'm doing wrong? Any tips?

Thanks!

Regards,
Fred

Re: Callibration

for the residual reading when no load is connected, i would recommend you look at the raw data directly of the analog input.

analog input is probably reading a 1 o 2 value. that when multiplied and done the maths ends up in some decimals of amps.

as for the calibration, you may need to do some further calibration at different loads, plot them in excel, and find a calibration factor that suits in general.

also dependes on the load, if the 25W device is something like a laptop or a old bulb, things can make a big difference

Re: Callibration

Its hard for CTs tr5o read low currents, if you're usinfg a CT.  Are you ure the load is 25 watts.  If using a CT double triple or even tens time wrap the wire thoruhg the CT to fool it into thinking the current is larger. Remeber only resitive loads have power factor of 1.  they are the only loads also that stay constant once they are at operating temp.

Re: Callibration

Any suggestions on the range of the PHASECAL I should test with?