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PDF ( 数据手册 , 数据表 ) ADE7761

零件编号 ADE7761
描述 Energy Metering IC
制造商 Analog Devices
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ADE7761 数据手册, 描述, 功能
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Energy Metering IC with On-Chip
Fault and Missing Neutral Detection
ADE7761
FEATURES
High accuracy active energy measurement IC, supports
IEC 687/61036
Less than 0.1% error over a dynamic range of 500 to 1
Supplies active power on the frequency outputs F1 and F2
High frequency output CF is intended for calibration and
supplies instantaneous active power
Continuous monitoring of the phase and neutral current
allows fault detection in 2-wire distribution systems
Current channels input level best suited for current
transformer sensors
Uses the larger of the two currents (phase or neutral) to
bill—even during a fault condition
Continuous monitoring of the voltage and current inputs
allows missing neutral detection
Uses one current input (phase or neutral) to bill when
missing neutral is detected
Two logic outputs (FAULT and REVP) can be used to indicate
a potential miswiring, fault, or missing neutral condition
Direct drive for electromechanical counters and 2-phase
stepper motors (F1 and F2)
Proprietary ADCs and DSP provide high accuracy over large
variations in environmental conditions and time
Reference 2.5 V ± 8% (drift 30 ppm/°C typical) with external
overdrive capability
Single 5 V supply, low power
GENERAL DESCRIPTION
The ADE7761 is a high accuracy, fault tolerant, electrical energy
measurement IC intended for use with 2-wire distribution
systems. The part specifications surpass the accuracy require-
ments as quoted in the IEC61036 standard.
The only analog circuitry used on the ADE7761 is in the ADCs
and reference circuit. All other signal processing (such as multi-
plication and filtering) is carried out in the digital domain. This
approach provides superior stability and accuracy over extremes
in environmental conditions and over time.
The ADE7761 incorporates a fault detection scheme similar to
the ADE7751 by continuously monitoring both the phase and
neutral currents. A fault is indicated when these currents differ
by more than 6.25%.
(continued on Page 3)
FUNCTIONAL BLOCK DIAGRAM
AGND
8
FAULT
15
VDD
1
V1A 2
V1N 4
V1B 3
MISCAL 7
ADC
ADC
ADC
A>B
HPF
B>A
A<>B
ZERO CROSSING
DETECTION
MISSING NEUTRAL
GAIN ADJUST
POWER
SUPPLY MONITOR
ADE7761
SIGNAL PROCESSING
BLOCK
LPF
V2P 6
V2N 5
ADC
2.5V
4k
REFERENCE
INTERNAL
OSCILLATOR
MISSING NEUTRAL
DETECTION
DIGITAL-TO-FREQUENCY CONVERTER
9
REFIN/OUT
14
RCLKIN
17
DGND
Figure 1.
10 11 12 16 18 19 20
SCF S1 S0 REVP CF F2 F1
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved.







ADE7761 pdf, 数据表
ADE7761
TERMINOLOGY
Measurement Error
The error associated with the energy measurement made by the
ADE7761 is defined by the following formula:
Percentage Error =
⎜⎛
⎜⎝
Energy
registered by ADE7761
True Energy
True
Energy
×
100%
⎟⎞
⎟⎠
Phase Error between Channels
The high-pass filter (HPF) in the current channel has a phase
lead response. To offset this phase response and equalize the
phase response between channels, a phase correction network is
also placed in the current channel. The phase correction net-
work ensures a phase match between the current channels and
voltage channels to within ±0.1° over a range of 45 Hz to 65 Hz
and ±0.2° over a range 40 Hz to 1 kHz.
Power Supply Rejection
This quantifies the ADE7761 measurement error as a percent-
age of reading when the power supplies are varied. For the ac
PSR measurement, a reading at nominal supplies (5 V) is taken.
A second reading is obtained with the same input signal levels
when an ac (175 mV rms/100 Hz) signal is introduced onto the
supplies. Any error introduced by this ac signal is expressed as a
percentage of reading (see the Measurement Error definition
above).
For the dc PSR measurement, a reading at nominal supplies
(5 V) is taken. A second reading is obtained with the same input
signal levels when the power supplies are varied ±5%. Any error
introduced is again expressed as a percentage of reading.
ADC Offset Error
This refers to the dc offset associated with the analog inputs to
the ADCs. It means that with the analog inputs connected to
AGND, the ADCs still see a dc analog input signal. The magni-
tude of the offset depends on the input range selection (see the
Typical Performance Characteristics section). However, when
HPFs are switched on, the offset is removed from the current
channels and the power calculation is not affected by this offset.
Gain Error
The gain error in the ADE7761 ADCs is defined as the differ-
ence between the measured output frequency (minus the offset)
and the ideal output frequency. The difference is expressed as a
percentage of the ideal frequency, which is obtained from the
transfer function (see the Transfer Function section).
Rev. A | Page 8 of 28







ADE7761 equivalent, schematic
ADE7761
The low frequency output of the ADE7761 is generated by
accumulating this active power information. This low frequency
inherently means a long accumulation time between output
pulses. The output frequency is, therefore, proportional to the
average active power. This average active power information can
in turn be accumulated (for example, by a counter) to generate
active energy information. Because of its high output frequency
and therefore shorter integration time, the CF output is propor-
tional to the instantaneous active power. This is useful for
system calibration purposes that would take place under steady
load conditions.
CH1
CH2
ADC
HPF
MULTIPLIER
ADC
DIGITAL-TO-
FREQUENCY
F1
F2
LPF DIGITAL-TO-
FREQUENCY
CF
INSTANTANEOUS
POWER SIGNAL –p(t)
INSTANTANEOUS
ACTIVE POWER SIGNAL
V×I
TIME
p(t) = i(t).v(t)
WHERE:
v(t) = V × cos(ϖt)
V×I
i(t) = I × cos(ϖt)
2
p(t) = V × I {1 + cos (2ϖt)}
2
Figure 20. Signal Processing Block Diagram
Power Factor Considerations
The method used to extract the active power information from
the instantaneous power signal (by low-pass filtering) is still
valid even when the voltage and current signals are not in
phase. Figure 21 displays the unity power factor condition and
a displacement power factor (DPF = 0.5), that is, current signal
lagging the voltage by 60°. If one assumes that the voltage and
current waveforms are sinusoidal, the active power component
of the instantaneous power signal (dc term) is given by
(V × I/2) × cos(60°)
This is the correct active power calculation.
INSTANTANEOUS
POWER SIGNAL
INSTANTANEOUS
ACTIVE POWER SIGNAL
V×I
2
0V
CURRENT
VOLTAGE
INSTANTANEOUS INSTANTANEOUS
POWER SIGNAL ACTIVE POWER SIGNAL
V×I
× cos(60°)
2
0V
VOLTAGE
CURRENT
60°
Figure 21. Active Power Calculation over PF
Nonsinusoidal Voltage and Current
The active power calculation method also holds true for
nonsinusoidal current and voltage waveforms. All voltage and
current waveforms in practical applications have some
harmonic content. Using the Fourier transform, instantaneous
voltage and current waveforms can be expressed in terms of
their harmonic content:
v(t) = VO + 2 × Vh ×sin(hωt + αh )
h0
(1)
where:
v(t) is the instantaneous voltage.
VO is the average value.
Vh is the rms value of voltage harmonic h.
αh is the phase angle of the voltage harmonic.
i(t) = IO + 2 × Ih ×sin(hωt + βh )
h0
(2)
where:
i(t) is the instantaneous current.
IO is the dc component.
Ih is the rms value of current harmonic h.
βh is the phase angle of the current harmonic.
Rev. A | Page 16 of 28










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