ade7880 Analog Devices, Inc., ade7880 Datasheet - Page 17

• Manufacturer Part Number: ade7880
• Description: Polyphase Multifunction Energy Metering Ic With Harmonic Monitoring
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
TERMINOLOGY
Measurement Error
The error associated with the energy measurement made by the
ADE7880 is defined by
Phase Error Between Channels
The high-pass filter (HPF) and digital integrator introduce a
slight phase mismatch between the current and the voltage
channel. The all digital design ensures that the phase matching
between the current channels and voltage channels in all three
phases is within ±0.1° over a range of 45 Hz to 65 Hz and ±0.2°
over a range of 40 Hz to 1 kHz. This internal phase mismatch
can be combined with the external phase error (from current
sensor or component tolerance) and calibrated with the phase
calibration registers.
Power Supply Rejection (PSR)
This quantifies the ADE7880 measurement error as a percen-
tage of reading when the power supplies are varied. For the ac
PSR measurement, a reading at nominal supplies (3.3 V) is
taken. A second reading is obtained with the same input signal
levels when an ac signal (120 mV rms at 100 Hz) is introduced
onto the supplies. Any error introduced by this ac signal is
expressed as a percentage of reading—see the Measurement
Error definition.
For the dc PSR measurement, a reading at nominal supplies
(3.3 V) is taken. A second reading is obtained with the same
input signal levels when the power supplies are varied ±10%.
Any error introduced is expressed as a percentage of the
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 gain and input range selection
(see the Typical Performance Characteristics section). However,
Measurement Error =
Energy
Registered
True
by
Energy
ADE
7880
−
True
Energy
×
100
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(1)
%
the HPF removes the offset from the current and voltage channels
and the power calculation remains unaffected by this offset.
Gain Error
The gain error in the ADCs of the ADE7880 is defined as the
difference between the measured ADC output code (minus the
offset) and the ideal output code (see the Current Channel ADC
section and the Voltage Channel ADC section). The difference
is expressed as a percentage of the ideal code.
CF Jitter
The period of pulses at one of the CF1, CF2, or CF3 pins is
continuously measured. The maximum, minimum, and average
values of four consecutive pulses are computed as follows:
The CF jitter is then computed as
Harmonic Power Measurement Error
To measure the error in the harmonic active and reactive power
calculations made by the ADE7880, the voltage channel is
supplied with a signal comprising a fundamental and one
harmonic component with amplitudes equal to 250mV. The
current channel is supplied with a signal comprising a
fundamental with amplitude of 50mV and one harmonic
component of the same index as the one in the voltage channel.
The amplitude of the harmonic is varied from 250mV, down to
250µV, 2000 times lower than full scale.
The error is defined by
Measurement Error =
Power
Maximum = max(Period
Minimum = min(Period
Average =
CF
JITTER
Registered
=
Maximum
Period
True
by
0
ADE
Power
Average
+
Period
−
7880
Minimum
0
, Period
0
, Period
1
−
+
4
True
Period
1
, Period
1
, Period
×
Power
100
2
+
%
2
Period
2
, Period
, Period
×
100
ADE7880
3
%
3
3
)
)
(3)
(2)