90E21/22/23/24

SINGLE-PHASE HIGH-PERFORMANCE WIDE-SPAN ENERGY METERING IC

Functional Description

14

January 10, 2012

3.5

MEASUREMENT AND ZERO-CROSSING

3.5.1

MEASUREMENT

The 90E21/22/23/24 has the following measurements:

• voltage rms

• current rms (L line/N line)

• mean active power (L line/N line)

• mean reactive power (L line/N line)

• voltage frequency

• power factor (L line/N line)

• phase angle between voltage and current (L line/N line)

• mean apparent power (L line/N line)

The above measurements are all calculated with fiducial error except

for frequency. The frequency accuracy is 0.01Hz, and the other mea-

surement accuracy is 0.5%. Fiducial error is calculated as follow:

3.5.2

ZERO-CROSSING

The ZX pin is asserted when the sampling voltage crosses zero.

Zero-crossing mode can be configured to positive zero-crossing, nega-

tive zero-crossing and all zero-crossing by the Zxcon[1:0] bits (MMode,

2BH). Refer to section 6.4.

The zero-crossing signal can facilitate operations such as relay oper-

ation and power line carrier transmission in typical smart meter applica-

tions.

100%

*

U

U

-

U

rror

Fiducial_E

FV

real

mea

=

Table-8 The Measurement Format

Measurement

Fiducial Value (FV)

90E21/22/23/24 Defined

Format

Range

Comment

Voltage rms

Un

XXX.XX

0~655.35V

Current rms

note 1, note 2

Imax

as 4Ib

XX.XXX

0~65.535A

Active/ Reactive Power

note 1

maximum power as

Un*4Ib

XX.XXX

-32.768~+32.767

kW/kvar

Complement, MSB as the sign bit

Apparent Power

note 1

Un*4Ib

XX.XXX

0~+32.767 kVA

Complement, MSB always '0'

Frequency

fn

XX.XX

45.00~65.00 Hz

Power Factor

note 3

1.000

X.XXX

-1.000~+1.000

Signed, MSB as the sign bit

Phase Angle

note 4

180°

XXX.X

-180°~+180°

Signed, MSB as the sign bit

Note 1: All registers are of 16 bits. For cases when the current and active/reactive/apparent power goes beyond the above range, it is suggested to be handled by

microcontroller (MCU) in application. For example, register value can be calibrated to 1/2 of the actual value during calibration, then multiply 2 in application. Note that

if the actual current is twice of that of the 90E21/22/23/24, the actual active/reactive/apparent power is also twice of that of the chip.

Note 3: Power factor is obtained by active power dividing apparent power

Note 4: Phase angle is obtained when voltage/current crosses zero at the frequency of 256kHz. Precision is not guaranteed at small current.