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ADE7878 Negative Power Reading

Question asked by chris-meters on Sep 17, 2015
Latest reply on Sep 21, 2015 by hmani



I am developing a meter using the ADE7878. The ADE7878 is mounted on a PCB with a circuit borrowed heavily from the development board and I am communicating with the chip using a microcontroller with SPI.


I am taking my voltage source from a wall socket and I am measuring the current using a 50A current transformer with an internal burden resister that outputs a 0.33Vac signal.


I have been using application note AN-1076 to help calibrate the chip. When I was calibrating the WGAIN register I was getting negative readings from the WATTHR register. Reading the ANGLE register it appears that the current and voltage signals are about 180 degrees out of phase which I think is causing the negative reading.


I have checked my CT connection. The positive wire from the CT is connected to a screw terminal on the PCB, from the screw terminal the signal goes through the circuit shown below to pin 7 (IAP) on the chip. The negative wire from the CT connects through to pin 8 (IAN) on the chip. The CT is also facing the right way for the flow of current.

CT circuit.PNG

The voltage connection is shown in the circuit below. My live connection of my voltage source is connected to VAP on the chip pin 23. My neutral connection is connected to VN on the chip pin 18.

Voltage circuit.PNG

I don't know the reason for this 180 degree phase shift between the current and voltage signals.


Does the circuit/setup described above look ok? Is there anything else I should be checking? Is there a settings within the ADE7878 chip I can check?


Any guidance would be much appreciated.


If you require more information please ask and I'll do my best to provide it.


Thanks in advance.