Hi kishore.r
Below is an example experiment that I conducted:
| Voltage signal applied | Amplitude |
| Fundamental - V1 | FS/2= 353.55mVrms/2= 0.17677Vrms |
| 3rd harmonic - V3 | FS/10=353.55mVrms/10=0.035355Vrms |
| 5th harmonic- V5 | FS/10=353.55mVrms/10=0.035355Vrms |
| 7th harmonic - V7 | FS/10=353.55mVrms/10=0.035355Vrms |
| Register | Values read back |
| HXVHD | 0.200075 |
| HYVHD | 0.200046 |
| HZVHD | 0.200077 |
| AVRMS | 2032862 |
| FVRMS | 1920092 |
| VTHD | 0.346662 |
Checking THD using applied signals:
Or in other words:
THD = sqrt(V3^2 + V5^2 + V7^2)/ V1 = 0.346410162 ( which is close to the register value read)
Checking THD using HD results:
THD = sqrt(HXVHD^2+HYVHD^2+HZVHD^2)= 0.346524478 ( which again matches with the read back THD value)
Also, VRMS/FVRMS register reading at full scale is : 3766572
The FVRMS register reading observed is 1920092, which is 1920092/3766572 of FS= 0.50977 of FS ( which is correct)
The AVRMS register reading observed is 2032862, which is 2032862/3766572 of FS= 0.539711 of FS.
If you compute VRMS by doing the sum of squares of V1,V3,V5 and V7 and then taking the square root of the result, you get 0.187082 Vrms which is 0.52915 of FS and hence correct as well)
Hope this clarifies your confusion! You can try a similar experiment to verify your results as well.
Regards
hmani