AS8228 datasheet(25/123 Pages) AMSCO

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Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 25 of 123

The default value of vconst is 2877 (0B3Dh) which translates into an equivalent Vmains value of 311V.

The energy is calculated using vconst and the selected current (i1 or i2) when sel_v in the SREG/Select

The vconst value may be calculated according to the formula:

RMS

vconst

Example: RMS_V = 479

⇒

479

vconst

= 2,128

Note: When vconst is used for the calculation of energy, sel_p must be set to ‘0’.

Low Pass Filter for Real Power (PLP)

When the instantaneous power is low pass filtered the result is practically a DC value for the power, which is

termed real power. It is generally preferred to use real power to generate pulses for the calibration, as the

duration between pulses is more constant (pulse jitter).

Corner frequency:

18.6Hz

The low pass filter ensures that the power output pulse jitter is minimised.

Direction Indicator (DIRO)

The direction indicator (DIRO) situated in the Status Register (Bit 4) defines the direction of the measured

power. The direction is determined by the phase relationship between the Mains voltage and selected Mains

current (i1 or i2).

When bit 4 in the Status Register is ‘0’, the Mains voltage and selected Mains current are in phase, thus

indicating positive energy flow. When bit 4 in the Status Register is ‘1’, the Mains voltage and the selected

Mains current have a phase reversal, indicating negative energy flow. The energy calculation (np) is generated

from positive energy, thus when DIRO = 1, the negative energy is converted to positive energy by the ‘Abs’

block shown in Figure 3:

AFE block diagram.

Should the meter application require unidirectional energy measurement, the MCU can separately derive both

the positive and negative energy values, depending on the status of the DIRO bit.

Accumulator for Real Power (P_ACCU)

To ensure that the power information transferred to the MCU is identical to that of the LED pulses, the P_ACCU

counts the pulses generated by Fast Pulse Gen. After ‘nsamp’ (nyquist) sampling periods an interrupt is sent to

the MCU requesting to fetch the new energy information. (Interrupt line ‘IE.0’ goes high and the ‘data available

interrupt’ (dai) flag in the SREG/Status register is set). The ‘ack’ bit in the SREG/Status register is also set to

1. If the MCU takes the energy information, it has to reset the ‘ack’ bit signalling that the energy information

(Once the voltage channel has been calibrated, 479

is the typical value when Vmains = 230V)

AS8228 Datasheet(PDF) 25 Page - ams AG