ADE7880 datasheet(19/104 Pages) AD

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Data Sheet

ADE7880

Rev. A | Page 19 of 104

TERMINOLOGY

Measurement Error

The error associated with the energy measurement made by the

ADE7880 is defined by

Measurement Error =

100

7880

−

Energy

True

Energy

True

ADE

Registered

Energy

(1)

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,

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:

Maximum = max(Period0, Period1, Period2, Period3)

Minimum = min(Period0, Period1, Period2, Period3)

Average =

Period

The CF jitter is then computed as

100

−

Average

Minimum

Maximum

JITTER

(2)

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 250 mV. The current

channel is supplied with a signal comprising a fundamental

with amplitude of 50 mV and one harmonic component of the

same index as the one in the voltage channel. The amplitude of

the harmonic is varied from 250 mV, down to 250 μV, 2000 times

lower than full scale.

The error is defined by

Measurement Error =

100

7880

−

Power

True

Power

True

ADE

Registered

Power

(3)

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