ADE7978 datasheet(27/120 Pages) AD

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Data Sheet

ADE7978/ADE7933/ADE7932

Rev. 0 | Page 27 of 120

TERMINOLOGY

Energy Measurement Error

The accuracy of the energy measurement is assessed as follows:

1. The voltage channel is supplied with a sinusoidal signal that

has peak values equal to ±250 mV. This value represents

half of the full scale.

2. The current channel is supplied with sinusoidal signals that

have peak values equal to ±31.25 mV (full scale), ±3.125 mV

(1/10 of full scale), ±312.5 µV (1/100 of full scale), ±31.25 µV

(1/1000 of full scale), and ±15.625 µV (1/2000 of full scale).

3. The energy is accumulated in line cycle accumulation mode,

and the accumulation time varies with the current channel

signal level.

The energy calculated for current peaks equal to ±3.125 mV

(1/10 of full scale) is considered the reference. The energy

measurement error is computed relative to a straight line that

passes through this point, as follows:

( )

100

)

(

)

(













−

1/10

Energy

AccTime

Energy

(1)

where:

Energy(Ix) is the energy measurement when the current is Ix.

Energy(I1/10) is the energy measurement when the current

is I1/10. This is the reference measurement.

AccTime(I1/10) is the accumulation time used to measure

Energy(I1/10).

AccTime(Ix) is the accumulation time used to measure

Energy(Ix).

I rms and V rms Measurement Error

The accuracy of the rms measurement is assessed as follows:

1. The voltage and current channels are supplied with sinu-

soidal signals of various peaks, starting with the full-scale

signals (±500 mV for the voltage channel and ±31.25 mV

for the current channel) and ending with ±1 mV and

±62.5 µV, respectively.

2. The rms registers are read at least once per line cycle over

1 sec and averaged.

The measurement performed when the input signal has peaks

equal to 1/10 of full scale is considered the reference. The rms

measurement error is computed relative to a straight line that

passes through this point, as follows:

( )

100

1 ×













−

1/10

rms

(2)

( )

(

)

100

1 ×













−

1/10

rms

(3)

where:

I rms(Ix) is the current rms measurement when the current is Ix.

I rms(I1/10) is the current rms measurement when the current is

I1/10. This is the reference measurement.

V rms(Vx) is the voltage rms measurement when the voltage

is Vx.

V rms(V1/10) is the voltage rms measurement when the voltage is

V1/10. This is the reference measurement.

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 the Nyquist

frequency, excluding harmonics and dc. The spectral compo-

nents are calculated over a 2 sec window. The value for SNR is

expressed in decibels.

Signal-to-Noise-and-Distortion (SINAD) Ratio

SINAD is the ratio of the rms value of the actual input signal to

the rms sum of all other spectral components below the Nyquist

frequency, including harmonics but excluding dc. The spectral

components are calculated over a 2 sec window. The value for

SINAD is expressed in decibels.

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of all harmonics (excluding

the noise components) to the rms value of the fundamental.

The spectral components are calculated over a 2 sec window.

The value for THD is expressed in decibels.

Spurious-Free Dynamic Range (SFDR)

SFDR is the ratio of the rms value of the actual input signal to the

rms value of the peak spurious component over the measurement

bandwidth of the waveform samples. The spectral components are

calculated over a 2 sec window. The value of SFDR is expressed

in decibels relative to full scale, dBFS.

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 follows:

100

−

Average

Minimum

Maximum

CFJITTER

(4)

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