Question asked by TeddyB. on Feb 15, 2016
Latest reply on Feb 22, 2016 by dlath

Hello

I am using a board with current transformer and AC/AC voltage transformer with ADE7753. While everything works, calibration gives me some major problems. I am using an accurate source, but I would also try to calibrate it with a reference meter as soon as I got most of the problems solved. Here is what I am struggling with:

- VRMS  register returns a value of about 26000 decimal when the V2P/V1N inputs are internally shorted and there is no signal. I tried with various combinations of CH2OS and VRMSOS, and so far the most effective is CH2OS = 0x24 and VRMSOS = -2048. This gives a value of around 1700 dec in VRMS for no signal condition. I want to make VRMS equal to zero when there is no signal; also ano other number loaded in CH2OS makes the VRMS value go higher and higher. On the other hand, I am able to make the IRMS register stay at zero for no current condition.

- I tried calibrating the meter several times using various loads with PF = 1. The problem after calibrating is that the LAENERGY register contains a value which is slightly higher than the contents of LVAENERGY register (both are scaled using the Wh/LSB and VAh/LSB constants). For example, for a 1 kW load with PF = 1, the values are 1040 W and 1035 VA. When I multiply and scale the current and voltage signals for the same load, I get 1080 VA.

Every time I perform a calibration I end up with more or less the same values for CFDEN and WGAIN. I always have a value of 0 for VAGAIN; is this a strange behavior? Here are the results of my last calibration:

CFDEN = 1916 dec

WGAIN = -2007

VAGAIN = 0

APOS = 23000

Wh/LSB = 0.00016301512780386018

VAh/LSB = 0.00009790546761651741

The PCB configuration is taken from the datasheet and everything else works as expected. I use the routine described at page 47 of the datasheet for calibrating VAGAIN and WGAIN simultaneously. Now I am stuck with this for days and can't continue working on my project. Any help will be greatly appreciated!

Regards