ADE7878 calibrated with a 230VAC single phase voltage, erroneous reading.

Discussion created by Audioberry on Jun 25, 2018
Latest reply on Jun 26, 2018 by Audioberry

The voltage is connected to all three VAP, VBP, VCP inputs in parallel. Then, if the voltage is removed from VBP-VCP and the VAP channel is separately tested, we get a half reading i.e. 115VAC. Why this?

Is it necessary to calibrate each channel separately? Or a real 3-phase voltage must be applied to all inputs so as the phase angle will be 120? 



We have located the problem. It is the input filter resistor of 1KOhms in parallel with the 22nF capacitor that is connected between the VN (Neutral input) and PCB ground. Probably this resistor work as pull-up and when we have a reading (we did again calibration of channel VAP) of 230V on VAP, in the other channels VBP and VCP although are disconnected, the reading is the half (115V) instead zero. I checked the voltage at all 3 inputs, in VAP is the expected 230mV but in VBP and VCP is 115mV while both are grounded during calibration. We get the measurements directly from the registers of ADE7858A, through SPI, to a Particle P1 Wi-Fi processor and we send them to our IOT application. During code development, we monitor the registers of ADE7858 in the IDE of Particle P1 through the offered Serial Monitor.  

What could we make? If the filter resistor is removed, and the Neutral input will be directly connected to PCB ground, probably the issue will be resolved. 

Is it wise this?

Thanks a lot for any help.