ADE7816 multiple issues while working on EVB

Hi all,

I am using AD7816 EVB to go through the working of IC. While working on it I am facing few issues while interpreting the values coming from IC.

First let me explain you my setup:

  1. I am using Rogowski coils(100mV/KA) connected on three channels A,B and C. And voltage from stable source i.e. Ponovo make Relay Test Kit.
  2. Voltage = 63v Current = 100A
  3. ADE7816 Register settings:-
    1. WTHR1 = 0x000002
    2. WTHR0 = 0x000000
    3. VARTHR1 = 0x000002
    4. VARTHR0 = 0x000000
    5. PCF_A_COEFF = 0x400CA4 (50Hz)
    6. PCF_B_COEFF = 0x400CA4 (50Hz)
    7. PCF_C_COEFF = 0x400CA4 (50Hz)
    8. PCF_D_COEFF = 0x400CA4 (50Hz)
    9. PCF_E_COEFF = 0x400CA4 (50Hz)
    10. PCF_F_COEFF = 0x400CA4 (50Hz)
    11. DICOEFF = 0xFFF8000
    12. GAIN = 0x49(PGA GAIN 2)
    13. CONFIG = 0x01 (enable integrator)

My issues:- 

  1. RMS value conversions factor:-
    1. From the data sheet I saw two formulas to convert the RMS raw values into real value
      1. Constant = (1/(Raw count/Input value))
      2. Constant = (Input/Count)*K
    2. I don't know which one to use.
  1. Gain Matching:-
    1. After reading AN-1152, it is not clear to me how to do Gain matching for Channel A before doing for others channels as it is mentioned use channel A as reference for gain matching. 
    2. How to do gain matching for Voltage Channel?
    3. Is gain matching is same as like calibration of Voltage and Current channel?
  2. I am not able to calculate frequency(50Hz) from the conversion formula given in DS. The value of the period register for 50 Hz networks is approximately 5120 (256 kHz/50 Hz) from DS, after putting this value frequency is coming around 30Hz. 
    1. Formula Fl = (0x256E3)/(period[15:0] + 1), this is not working for me.
  3. Angles:-
    1. When I give load on two channels only then I will get stable readings from only one channel. After applying load on all channels I am getting stable readings for all three channels. So is there any rule to give load on all channels?
    2. If I changes channel A angles and keep B and C angles as 0deg, then I can see variations proportional to change in Channel A values. If I do the same thing with channels B and C, then I am getting constant values from the registers there is no change values with variation.I

I have attached the jumper settings of my EVB. 

Your earlier response will be great for me.

Thank You & Regards

  • Hello 

    1.   Here you are referring to the calibration steps. AN-1152,pag8 :
      1. Constant = (1/(Raw count/Input value)) =>  Constant = (1/(Raw count/Input value)) = Input value/ Raw count
      2. Constant = (Input/Count)*K => Constant = (1/(Raw count/Input value)) = Input value/ Raw count *k
        1. Input value = know value defined on the source reference. Raw count = ADE value. k is used for format conversion but has no additional information.  
    2. Gain Matching: 
      1. you should try to have the same ADC input dynamic range in all current channels. In this way you just need to calibrate one phase for both V and I and then report the calibration results on the other channels.
      2. How to do gain matching for Voltage Channel? You just have one voltage channel so you don't need to match it
      3. Is gain matching is same as like calibration of Voltage and Current channel? Not for ADE7816
    3. The period register for 50 Hz networks is approximately 5120 (256 kHz/50 Hz) from DS, after putting this value frequency is coming around 30Hz.: Formula (17b) = (0x256E3)/(period[15:0] + 1) = 256000/(5120+1) = 49.99. I understand that the 0x256E3 might be confusing.
    4.  Angles:-
      1. Angle are measured between channels (Tabel 10)