Datasheet

ADE7854/ADE7858/ADE7868/ADE7878 Data Sheet
Rev. G | Page 22 of 100
TERMINOLOGY
Measurement Error
The error associated with the energy measurement made by the
ADE7854/ADE7858/ADE7868/ADE7878 is defined by
Measurement Error =
%100
78
×
−
Energy
True
EnergyTrue
xx
ADEby
RegisteredEnergy
(1)
Power Supply Rejection (PSR)
This quantifies the ADE7854/ADE7858/ADE7868/ADE7878
measurement error as a percentage 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 twice the fundamental frequency) 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
However, 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 ADE7854/ADE7858/
ADE7868/ADE7878 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:
Maximum = max(Period
0
, Period
1
, Period
2
, Period
3
)
Minimum = min(Period
0
, Period
1
, Period
2
, Period
3
)
Average =
4
3210
PeriodPeriod
PeriodPeriod ++
+
The CF jitter is then computed as
%100×
−
=
Average
MinimumMaximum
CF
JITTER
(2)
Signal-to-Noise Ratio (SNR)
SNR is the ratio of the rms value of the actual input signal to
the rms sum of all other spectral components below 2 kHz,
excluding harmonics and dc. The input signal contains only
the fundamental component. The spectral components are
calculated over a 2 sec window. The value for SNR is expressed
in decibels.
Signal-to-(Noise and Distortion) Ratio (SINAD)
SINAD is the ratio of the rms value of the actual input signal
to the rms sum of all other spectral components below 2 kHz,
including harmonics but excluding dc. The input signal
contains only the fundamental component. The spectral
components are calculated over a 2 sec window. The value
for SINAD is expressed in decibels.