Archived Forum

The calibration coefficients in the sketches are starting values. Follow the calibration procedure here to get the actual correct values for your particular set of components. It's quite possible that all 3 CT inputs will have different coefficients, as each use a different CT and burden resistor.

The value for the voltage calibration in the V2.2 sketch may well be the one for the old Mascot adapter, why there are different values for each CT, I've no idea. The best possibility I can think of is an attack of digitus erroneous whilst editing. They should all be the same.

Just wanted to check, am I supposed to be calibrating the emontx using the same socket that I intend powering the 9v from or from any socket in the house?

Using my Fluke 117 I managed to calibrate the Vrms. But I just wanted to check how this was supposed to be done. 

I took a reading using the LoZ but that keeping jumping around too much. So instead I used the normal Voltage setting and used the Max/Min/Average setting and let the meter run for about a min and used the Avg over 60 seconds as my measured value. 

Moving to the AC current calibration is a bit more tricky. I have never measured AC current before and my normal method of putting the meter in series with the load (as I would have done for DC) doesn't seem to work. The voltage doesn't seem to be flowing through the meter and so the load won't even switch on. What am I doing wrong. My meter leads are on the 10A slots and the meter dial is on the AC Amp setting. 

Yes, I know the feeling if you're using the normal mains (if yours is anything like mine). All you can do is get as close as possible, initially. What's been reported as a method is you then compare accumulated kWh against your supplier's meter (which by definition is 100% accurate even if it actually isn't!) and trim the calibration by small amounts until you get as close as you can. Better than 1% has been claimed.

I'm afraid I don't have a Fluke, so all I can suggest is (a) there is a fuse for the 10 A range - is it intact? and (b) read the manual! But what you're doing sounds right. I assume your load is less than 10 A and has no significant inrush (which might have blown the fuse even if the nominal current is less than 10 A).

Before I can use the meter reading method to start calibration I wanted to get the Vrms, CTs and phase done atleast manually.

Looks like I'm going to have my plug in energy monitor for current instead of my multimeter.

looks like my 11a fuse is blown, so I used my Energenie plug in energy meter. I compared the voltage between my Fluke and the energy meter, they were about 0.5 volts apart, so that was ok.
After calibration my emontx and my inverter reported the same usage after a day, down to the decimal point! Brilliant.
There is about a 0.1 difference between the emoncms feed value and the My Solar App report. But this is a great result, and I've just started.

The important point there is, how did you blow the fuse? You need to know that because if ever you were to rely on a zero current indication and the fuse had just blown (again), you could get yourself into serious trouble. Not quite as serious though as if you relied on a no voltage indication (if you have a fused probe - most meters don't fuse the voltage ranges, I think for exactly this reason) and the circuit was in fact live.

Anyway, I'm glad to hear you're pleased with the result.

My fuse didn't blow trying to do this. It was blown prior to even starting this project!

It was still worth noting the dangers, we don't want to lose you!