90E21 Datasheet, PDF (14/57 Pages) Integrated Device Technology – Single-Phase High-Performance Wide-Span Energy Metering IC

90E21/22/23/24
SINGLE-PHASE HIGH-PERFORMANCE WIDE-SPAN ENERGY METERING IC
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:
Fiducial_E rror = ^{Umea - Ureal} * 100%
U_FV
Where U_mea is the measured voltage, U_real is the actual voltage and
U_FV is the fiducial value.
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}
Active/ Reactive Power^{note 1}
Apparent Power^{note 1}
Frequency
Power Factor^{note 3}
Imax
as 4Ib
maximum power as
Un*4Ib
Un*4Ib
fn
1.000
XX.XXX
XX.XXX
XX.XXX
XX.XX
X.XXX
0~65.535A
-32.768~+32.767
kW/kvar
0~+32.767 kVA
45.00~65.00 Hz
-1.000~+1.000
Complement, MSB as the sign bit
Complement, MSB always '0'
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 2: The accuracy is not guaranteed when the current is lower than 15mA. Note that the tolerance is 25 mA at I_FV of 5A and fiducial accuracy of 0.5%.
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.
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.
Functional Description
14
January 10, 2012