AS8228 datasheet(24/123 Pages) AMSCO

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Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 24 of 123

Calibration of V and I Channels

The single channel data may be corrected with a 16-bit calibration value.

The calibration range is [1 LSB; 2 – 1 LSB], step size (1 LSB): 3.052 x 10

-5.

Calibration Register Setting

Value

0000h

0001h

0.00003052 (= 1 LSB)

…

2000h

0.25

…

4000h

0.5

…

8000h

1.0

…

FFFFh

1.99996948 (2 – 1LSB)

The V and I channel RMS calculation and calibration is described below (V and I channel are identical, thus

only the I channel is shown):

The ideal values after RMS calculations of voltage and current are:

RMS_V(ideal) = 479(rms)

RMS_I(ideal) = 292,110(rms)

These values assume ideal input conditions with Vin = 100mVp at rated conditions and Iin = 30mVp (Gain = 20)

at rated conditions.

e.g: Imax = 60A → 292,110 ≅ 60A

Ical = 10A →

685

110

292

)

ideal

RMS

≅

Due to non-ideal components a different RMS value is calculated: RMS_I(actual). From this, the required

calibration factor is calculated using the following formula:

)

actual

RMS

)

ideal

RMS

cal

The following formula calculates the actual value to be programmed into the calibration registers (cal_v; cal_i1;

cal_i2):

))

768

cal

(

round

(

hex

)

reg

cal

Constant Voltage Register (vconst)

The vconst registers (9334h and 9335h) provide a predefined voltage value that can be used for calculating

energy when the Vmains is not available.

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