Hello all,

I have been trying to calibrate the ADE7758 for use in reading Vrms, Irms, WT/Hr, VA/Hr, and VAR/Hr. I feel that I have figured out the Vrms and the Irms pretty well and am able to get readings to within a volt RMS. My question comes from trying to calibrate the WT/hr reading.

I understand the concept of trying to match a coefficient to turn the register readings into real world values. And I plan on making more than one of these and one app note I read mentioned being able to calculate the coefficient once and then calibrating all the meters such that the coefficient will work for all of them.

So my method of attack on the Vrms and Irms was to calculate the ideal slope of the register readings vs excitation values. I based this calculation off of the approximate max value the Vrms register which was about 1.6 million.

My problem now, is trying to do the same for the WT/hr register. I found equation 60 on page 50 of the datasheet, but I don't think it it the right equation for where it is placed in the datasheet. The equation looks more like an equation of reading the pulse output and calculating that to a real-world value. In my setup, I will have no use for the pulse outputs and don't want to mess with calibrating them. In addition, I plan on using an accurate source for calibrating these devices.

So in short my question is, how can I calculate the ideal value for the xWATTHR register? Without having to 'arbitrarily' pick a MC constant and calibrate the divider for that frequency. Any input would be appreciated.

Hi Trevor,

First off I want to be sure there is no confussion in the parts measurement, the energy register read the Watt*Hour measurement not the Watts per hour.

There are two techniques to go about calibrating the part:

1) To calibrate the part in order to get actual real world values from the register, just note that this may in some cases affect things such as your dynamic range.

2) The other is to calibrate with the maximum register values in mind, to get the best dynamic range and use a calculated Wh/LSB value to convert the register value to a real world reading. A V/LSB and A/LSB for the rms registers which it sounds like you have done.

Which method is up to you and the needs of your application. Equation 60 on page 50 is meant more for a meter being calibrated by reading the pulse outputs and in the case that you are not you can simplify the equation. Once you have calculated a Wh/LSB then you can use the equation below:

With this your calibration will be based on this Wh/LSB value rather than a Impulses/Wh value.

Regards,

Dlath