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ADE7758 Watt Gain Calibration

Question asked by pico20191 on Aug 5, 2014
Latest reply on Aug 12, 2014 by hmani

I have been trying to optimize a calibration routine for the ADE 7758.  The results are not good.


Let me start with a simple question regarding how to derive the Watt Gain register setting using Line Accumulation and an Accurate Source.


I do not need the pulse output for anything. Can I ignore the CF registers (leave as default)?  If not, what should I set them to?


Also, what is the (4 * Meter Constant) in the equation required for?  I have no meter to provide me with a constant, so I simply chose 3200.  Is this okay?


My setup is power factor = 1, providing about 120V, at about 10 Amps, and the line frequency is 60Hz.  I am calibrating one phase at a time.  My accumulation time is 15 seconds.  I have no WDIV factor applied right now, so the register has been left at the default setting.


If I calculate the expected value based on equations 60 and 61, I get either 64d or 4032d depending on whether I include the 0x3f default in the APCFDEN register as a factor in the equation. However, when I read the raw value from the WATTHR register after 15 seconds, I get 0x4060, or 16,480d.  If I then try to compute a register value using expected and the accumulated WATTHR number, the result is obviously wrong.


For example,

((4032 / 16,480) - 1) * 2^12 = -3094.  That is a register overflow given a signed 12 bit register.


I know from experiments that the proper adjustment is typically not < -150 or > +150.


I have made sure that the WATTHR register is cleared before i begin the accumulation step.


Can someone advise me as to what I am doing wrong?


Thanks so much!