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Hi Gerard,

Sorry for the slow reply, I've got round to doing some lab testing today to investigate the problem. 

The problem was caused by a new batch of AC-AC adapters we are using (new adapters are better, the don't have a +2V offset see: http://openenergymonitor.blogspot.com/2011/12/ac-ac-adapters.html), the calibration in the code was not updated to reflect the change. 

The new code is as follows:

The voltage examples on github have been updated and the Single CT Voltage example has been made to work with Arduino 1.0

emon1.setPins(2,0);                    //emonTX AC-AC voltage (ADC2), current pin (CT2 - ADC0)
emon1.calibration(234.89,126.5,1.7);   //voltage calibration , current calibration, power factor calibration
emon1.calc(20,2000,vcc );              //No.of wavelengths, time-out , emonTx supply voltage 

 Hi Glyn,

Thanks for the reply.  I'll give that a go. 

However I'm not using one if your tx's- rather one I had lying around

Would you mind at your convenience just explaining How you arrive at the calibration figures so I can recalibrate for my tx if necessary. 

Kind regards

Gerard

 I came up with the calibration values be comparing the power reading, voltage reading and PF reading with a plug-in energy monitor and a bit of ittrative trail and error. Basicly just change the calibration values untill the energy monitor readings match what the plug-in monitor reads. 

I calibrated the voltage first, then current then PF. 

New calibration value = (Old value/ new value) * current calibration coefficient 

emon1.calibration(voltage cal , current cal ,PF cal); 

The way I calculated the calibration figures was to first of all change the defaults to emon1.calibration(100.00,100.00,1.0); and took note of the figures coming out of the serial monitor, at the same time used a plug in energy monitor to obtain the actual figures being used.

Take for example a Hair Dryer I had, the figures coming out from the serial monitor was VMRS = 105.89, IRMS = 6.89, the plug in monitor gave me Volts = 241 and Amps = 8.42, using that I can calculate the calibration figures.

( Volts * 100) / VRMS = Calibration figure , which is  ( 241 * 100) / 105.89 = 227.59

( Amps * 100) / IRMS = Calibration figure , (8.42 * 100) / 6.89 = 122.20

The reason I was 100.00 as the initial figure and not 1.0 was is gave me better precision in my calculation.

In order to calculate the Power Factor you need to add "powerFactor1 = emontx.real1 / apparent1;" in the Measure from CT1 section and print out the variable in the serial_ouput section using "Serial.print(powerFactor1);"

If you then do the same for other household items such as Vacum Cleaner, Iron, Heater, Fridge etc you get a range of figures but all should be roughly in the same ballpark, my voltage figures were between 227.59 to 230.55, all I did was take the average to get the figure I went with.

As Glyn says there is a bit of trail and error involved, but you can get pretty accurate, for instance my setup is within 5 watts of what my solar inverter is saying its generating.

Hope that helps

Hi all,

Thanks again for your comments - Ive followed the procedure as above and found that the device is now calibrated to the correct readings. A little trial and error was indeed required.

Thanks again for your time

Regards

Gerard