AS8218 datasheet(120/123 Pages) AMSCO

120 / 123 page

Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 120 of 123

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

Fast internal pulse rate (PRint):

The Fast Pulse Gen output always has the same relationship with the LED pulse rate, which is defined by

mconst. Only if LED is calibrated to a meter constant different from those provided in the mconst table, will the

fast internal pulse rate be different.

[]

kWh

mconst

Rate

Pulse

arg

800

204

Where mconst is the meter constant.

[]

600

000

int

Active power calibration (Pulse_lev):

The Pulse_lev is specified such that a typical pulse rate of 204,800i/kWh can be achieved.

During energy pulse calibration the correct Pulse_lev is determined in order to get the desired pulse rate.

The IC default value for Pulse_lev is defined for Imax=40A and Vmains=230V.

Default Pulse_lev:

570,950

The formula for calculating the ideal Pulse_lev is as follows:

)

default

(

lev

Pulse

230

)

ideal

(

lev

Pulse

max

mains

The standard or reference meter pulses are counted between two pulses from the meter under test. From the

deviation the corrected Pulse_lev may be calculated.

)

ideal

(

lev

Pulse

)

corrected

(

lev

Pulse

Where Ni is the ideal number of pulses and Na is the actual number of pulses (pcnt register in MPIO).

The ideal number of pulses Ni is the ratio between the pulse rates, which is always >1. The formula for Ni is as

follows:

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