AN3398 datasheet(8/11 Pages) STMICROELECTRONICS

8 / 11 page

Calibration flow chart

AN3398

8/11

Doc ID 018812 Rev 1

R1 = R2 * (Vn - VDIV) / VDIV [Ohm]

Rogowski coil - Constant R1

As before, the voltage divider sensitivity is fixed, therefore, resistor values R1 and R2 are the

known values of the voltage divider resistor.

From the values above and for both the given amplification factor Ai and the initial calibration

data, the following target values can be calculated:

Voltage divider output:

Equation 19

VDIV = Vn * R2 / (R1 + R2)

Target RMS reading for given Vn:

Equation 20

XV = (VDIV / VREF) * Av * Kv * Kint_comp * len_u

Target RMS reading for given In:

Equation 21

XI = f * len_u * len_i * DUD / (FM * XV)

From which current sensor sensitivity KS is obtained:

Equation 22

KS = XI * VREF * 1000 / (In * Ai * Ki * Kint_comp * Kint * len_i) [mV/A]

Rogowski coil - Constant KS

The sensor’s nominal value of sensitivity must again be known, for example, it is KS.

From the values above and for both the given amplification factor Ai and the initial calibration

data, the following target values can be calculated:

Target RMS reading for given In:

Equation 23

XI = In * KS * Ai * Ki * Kint * Kint_comp * len_i / (VREF * 1000)

Target RMS reading for given Vn:

Equation 24

XV = f * len_u * len_i * DUD / (FM * XI)

Voltage divider output:

Equation 25

VDIV = XV * VREF / (Av * Kv * Kint_comp * len_u)

From which R1 resistor value is obtained:

Equation 26

AN3398 Datasheet(PDF) 8 Page - STMicroelectronics