SA9904APA Просмотр технического описания (PDF) - South African Micro Electronic Systems

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SA9904APA

Three Phase Power / Energy IC with SPI Interface

South African Micro Electronic Systems 

SA9904A

sames

USING THE REGISTER VALUES

ACTIVE AND REACTIVE ENERGY REGISTER

The active and reactive energy measured per count can be

calculated by applying the following formulae:

Energy per count = (VRATED x I ) RATED / 320000

The active and reactive power measured by the SA9904A is

calculated as follows:

Power = (VRATED x IRATED x N / INTTIME / 320000

(In watt seconds or var seconds)

Where:

VRATED Rated mains voltage of meter

IRATED Rated mains current of meter

N

Difference in register values between

successive reads (delta value)

INTTIME Time difference between successive register

reads (in seconds)

MAINS VOLTAGE REGISTER

The RMS voltage measurement is accurate to 1% in a range of

50% to 115% of rated mains voltage. The RMS mains voltage

measured by the SA9904A is calculated as follows:

Voltage = VRATED x VREGISTER VALUE / 700

VRATED

Rated mains voltage of meter

VREGISTER VALUE

Voltage register value

MAINS FREQUENCY REGISTER

Bits D0 to D9 represents a counter value that is scaleable to the

mains frequency measured.

The mains frequency measured by the SA9904A is calculated

as follows:

Frequency = FCRYSTAL / 256 / FREGISTER VALUE

FCRYSTAL

The external crystal frequency.

FREGISTER VALUE

Bits D9 to D0 of the frequency register.

Bits D10 to D20 are not used in the frequency register.

The phase error status may be ascertained from bits D21

and D22, as shown in the following table:

Frequency

data Bits

D22 D21

0

0

1

0

X

1

Description

No phase error

Phase sequence error (2 phases swapped)

Missing phase

The phase error status is merged on all three frequency

registers.

Bit D23 is set with a rising edge of the mains voltage and

cleared after 2ms.

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