I'm using the ADE9000 EVAL board.
I'm not using the onboard resistor divider for the voltage channels, but a standard 230V:12V (actual output voltage is around 13.8V) voltage transformer, followed by a 2k:100k resistor divider which is placed in parallel with the dual 1k resistors (by soldering the wire directly to a pad) that the ADE9000 xVAP & xVAN channels are connected across.
The divider gives an output voltage of around 91mV (RMS measured between VxP & VxN) ) when the input of the transformer is connected to 230VAC .
The current channel consists of a 10A CT (1:1500) ratio, with a center tapped 44ohm resistor (dual 22ohm), which is connected to the IxP, AGND & IxN inputs.
I've managed to calibrate & derive the conversion constants for voltage & current using the ADE9000 evaluation software. I did this by connecting all 3 inputs to a single AC phase (to ensure that the voltage & current inputs to all inputs was the same), setting load current to exactly 10A (by setting a variable resistance to obtain 10A from a 230V source). I measured the voltage displayed by the reference meters (around 230VAC), current (which was set to 10A) and pressed the button in 'Quick Startup' to generate the constants. Note that this was done at unity PF.
The constants for voltage & current work & the readings I obtain match what my reference meters display (Fluke & Yokogawa PQ analyzers).
I later noticed that the eval software recommends using 0.5PF to generate the constants, so I adjusted the RL load to obtain 10A at roughly 0.51PF, and pressed the button.
The constants generated for voltage & current were similar to the ones generated using a PF of 1.0, but there is a significant difference in the power & energy constants.
I performed a load test across the input range (10A) in single phase, with the load wire passing through all 4 CTs (A,B,C & N). Using the xWATT constants generated using the original 10A current at 1.0PF, I calculated the value of power using AWATT * conversion constant = actual value, and the value was within 5% of the reference meter. However, when a RL load was used, the values of power began drifting & were incorrect.
I tried using the constants that were generated using 0.5PF 10A load, but those constants also result in incorrect values of converted power.
These are the constants generated:
233V Vin, 10A @ PF = 1.0 | ~233Vin, 10A @ PF = 0.5 |
---|---|
Register Name - Calibration constant - Unit AIRMS 4.616269E-7 A/LSB | Register Name - Calibration constant - Unit AIRMS 4.585139E-7 A/LSB |
Note that although the conversion constants for I & V are the same in both cases, the values for xWATT, xVAR (and the corresponding energy values) differ significantly. The formula for conversion constants in the ADE9000 guide makes no distinction between the values of xWATT, xVAR & xVA; but that's obviously not the case here.
One more issue is that the conversion constant generated here for AWATT (even the correct one that's generated at PF=1.0) is negative for some reason. The Waveform buffer shows that there is no polarity error i.e. voltage & current are in phase, so the negative sign should not be present.
- How do I calculate the value of VLEVEL & what does this influence? The example in the documentation states VLEVEL = x * 1144084, where x is the dynamic range. Since my voltage channel outputs around 91mV at nominal voltage, dynamic range = 0.707/0.091 = 7.76923. Therefore, VLEVEL = 7.769*1144084 = 8888652 = 0x87A14C. Is this calculation correct?
- Why does the evaluation software different conversion constants for xWATT,xVA & xVAR? The technical reference manual's conversion constant section shows a common formula for similar values eg xWATT,xVA & xVAR (and a common value for xKWh,xVAh,xVARh)
- What's the recommended method of calibration? I connected all voltage inputs to a single phase, and the wire that carried the load current was passed through all the CTs. This was done to ensure that I could enter the voltage & current in the eval software, since there is only one field; and I figured it's likely to work better if a common voltage & current is fed to all inputs.
- At what PF should calibration be performed?
- Does the energy constant generated by the eval software need to be multiplied by the AWATTHR_HI directly (instead of taking a reading from AWATTHR_LO?)
Hi avnrdf,
How do I calculate the value of VLEVEL & what does this influence?
VLEVEL register is used for extract the fundamental from the total measured signal to make measurements include fundamental IRMS, Vrms and so on. If you are not interested in fundamental parameters, you can ignore this register.
Why does the evaluation software different conversion constants for xWATT,xVA & xVAR?
The evaluation software is used in some specific situation, you can calculate the conversion constants by yourself, and this will help you get more familiar with the chip.
What's the recommended method of calibration?
You can follow the ADE9000 user guide 1098 to do the calibration, the goal of calibration is get a good accurate data, you don't need to make all the path with the same signal. When you apply your circuit to the real situation, you should calibrate the chip again for different environment.
At what PF should calibration be performed?
That can be determined by in which PF your meter will be used, PF indicates the phase between voltage and current.
Does the energy constant generated by the eval software need to be multiplied by the AWATTHR_HI directly (instead of taking a reading from AWATTHR_LO?)
If you want to improve the precision, you can use AWATTHR_LO register.
Best regards,
Gary