AN2159

Converting readings into measured values

Doc ID 11400 Rev 3

21/23

For momentary values it is necessary first of all to evaluate their sign:

if (x_i_mom & 0x08000)

// positive current

x_i_mom = x_i_mom & 0x07FFF;

else

// negative current

{

x_i_mom = 0x08000 - x_i_mom;

x_i_mom = x_i_mom * (-1);

}

if (x_u_mom & 0x0400

// positive voltage

x_u_mom = (x_u_mom) & 0x3FF;

else

// negative voltage

{

x_u_mom = 0x0400 - (x_u_mom);

x_u_mom = x_u_mom * (-1);

}

The current and voltage conversion formulas in case of Rogowski Coil current sensor are:

u_rms = (1+R1/R2) * x_u_rms *Vref /(Au * Ku * Kint_comp * len_u * Kut)

i_rms = x_i_rms * Vref /(Ks * Kf * Ai * Ki * Kint * Kint_comp * len_i)

u_mom = (1+R1/R2) * x_u_mom * Vref /(Au * Ku * Kint_comp * len_u_mom * Kut)

i_mom = x_i_mom * Vref /(Ks * Kf * Ai * Ki * Kint * Kint_comp *

len_i_mom)

In case of current trasformer or Shunt sensor the formulas become:

u_rms = (1+R1/R2) * x_u_rms *Vref /(Au * Ku * Kint_comp * Kint * Kdif * len_u * Kut)

i_rms = x_i_rms * Vref/(Ks * Ai * Ki * Kint * Kint_comp * Kdif * len_i)

u_mom = (1+R1/R2) * x_u_mom * Vref /(Au * Ku * Kint_comp * Kint * Kdif * len_u_mom *

Kut)

i_mom = x_i_mom * Vref /(Ks * Ai * Ki * Kint * Kint_comp * Kdif * len_i_mom)