Hi,

I need to calibrate the ADE7753 for IRMS and VRMS. The input voltage is 230V and the load is a heater of 150W. I am reading out rms register value for both voltage and current. The voltage scaling factor is 0.0585, to convert the VRMS register value to volts. The current scaling factor is 0.606, to convert the IRMS register value to amps. The voltage reading (after factor multiplicaiton) comes out with an offset of +/-5V i.e. some times 225V or 233V etc.

As explained in the data sheet page 45, to compute value for the VRMSOS (equation 65). But computing the value for the VRMSOS is a bit confusing. What values of V1 and V2 should be considered (and the respective VRMS registers value to be noted), so that the value for the VRMSOS be calculated? and same for current IRMS?

If i take input voltage V1=230V and read out the VRMS value, then set input voltage V2=210V and again note the VRMS value. Compute VRMSOS using equation 65 and load the value into the VRMSOS register, but this does not do any calibration for the VRMS.

Any help in this regard will be appreciated.

Regards

Adnan Akhtar

Hi Adnan

The offset here refers to the non-zero reading that you will get in the register reading when very low inputs are applied. This is due to the noise dominance at low signal levels. To counteract this situation, offset calibration can be done. If your full-scale is 500 mV(FS), set V1 corresponding to 250 mV(FS/2) and V2 corresponding to 25 mV( FS/20; V1/10). Now read the corresponding RMS readings and substitute in the equation 65 of the datasheet, to get VRMSOS. Using this value, the rms register readings will be prone to less errors at low signal levels.

Regards

hmani