Hi All,
I posted this yesterday in the "General" section but maybe this is more applicable in the "Software" area - I hope the double post is not an issue...
Ive recently completed a build of the EmonTX (previously using Mains Non-Invasive V3).
After looking through the various firmware options I've been using the following firmware https://github.com/openenergymonitor/emonTxFirmware/tree/master/emonTx_1CT_Voltage
as I wish to monitor both voltage and current (one CT). To do this im using a 9v transformer to measure mains voltage. However, my values are off by quite a bit.....for example the EmonTX output monitored via its serial port (real, apparent, VRMS, IRMS, supplyV)
7.59 82.53 343.41 0.24 3164
In relation to the firmware above - could anybody explain the numbers in the calibration code here...
emon1.calibration(357.6,126.5,0);
emon1.calc(20,2000,vcc );
I think I need to substitute these for my own. Im also confused as the previous V3 firmware had declarations for the number of CT turns, burden resistor value etc. to calculate the scaling factor - none of these are mentioned in the firmware above. Thus, where my mains voltage is 240V (238V at present) the EmonTX is returning 343.41.
In addition, I have the CT connected at present to channel 1 (changed code to reflect this), however there is no wire through it at present so it cannot be reading any current. Yet however, Im showing an apparent and real power measurement. Obviously this would introduce errors into the system at times whereby voltage is being measured byt current consumption is zero or practically zero. Indeed with the above example the current consumption is nearly 0 at 0.24a but still the power calculations are off.
I am using an SCT-013-000 CT - it came with the EmonTX kit. Anybody know how many turns is on this CT?
Thanks in advance for your time - hopefully somebody can shed some light on this - or explain how I can calibrate the EmonTX properly.
Kind regards
Gerard Gallagher
Re: EmonTX 1CT Voltage questions regarding calibration
Anybody here has a good method of calibrating?
From what I understand, the calibration parameters set the VCAL, ICAL and PHASECAL variables. However, while VCAL and ICAL are used to get from the measured current and voltage to Irms and Vrms, PHASECAL is used to get from the measured voltage to a phase corrected voltage to calculate the real power. This means that the VCAL and ICAL are not used to calulate the real power usage, as the VCAL and ICAL are applied later on:
This is what I guess:
However, if the measured current is wrong, how can the measured real power ever be correct? Or is this where the V_RATIO and I_RATIO are helping out? What are those values anyway?