ADE7816 datasheet(26/48 Pages) AD

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ADE7816

Data Sheet

Rev. 0 | Page 26 of 48

POWER QUALITY FEATURES

This section describes the power quality features that are available

in the ADE7816.

SELECTING A CURRENT CHANNEL GROUP

When using the power quality features on the current channels,

the group of channels to be monitored must be selected. Bit 14

(CHANNEL_SEL) of the COMPMODE register (Address 0xE60E)

can be used to make this selection. To select the A, B, and C current

channels for the current channel power quality measurements,

CHANNEL_SEL must be set to 0 (default). To select the D, E,

and F current channels for the current channel power quality

measurements, CHANNEL_SEL must be set to 1. If all channels

require monitoring, the monitoring must be done in series by

modifying the CHANNEL_SEL bit after data is obtained. The

settling time of each power quality measurement is provided in

the section that pertains to each power quality feature.

INSTANTANEOUS WAVEFORMS

The ADE7816 provides access to the current and voltage channel

waveform data. This information allows the instantaneous data

to be analyzed in more detail, including reconstruction of the

current and voltage input for harmonic analyses. These measure-

ments are available from a set of 24-bit, signed registers. The

voltage channel has a dedicated register, VWV (Address 0xE510),

whereas the current channels share three registers: IAWV/IDWV

(Address 0xE50C), IBWV/IEWV (Address 0xE50D), and ICWV/

IFWV (Address 0xE50E). A group of current channels (A, B, C

or D, E, F) must be selected by Bit 14 (CHANNEL_SEL) of the

COMPMODE register (see the Selecting a Current Channel

Group section).

All measurements are updated at a rate of 8 kHz. The ADE7816

provides an interrupt status bit, DREADY (Bit 17 of the STATUS0

allowing measurements to be synchronized with the instanta-

neous update signal rate. The instantaneous update signal can

also be configured to trigger an interrupt on the external pin

by setting the DREADY bit (Bit 17) in the MASK0 register

(Address 0xE50A). With the specified full-scale analog input

signal of 0.5 V, the expected reading on the current and voltage

waveform register is approximately ±5,989,256 (dec).

The instantaneous waveforms have no additional settling time,

and, therefore, if the CHANNEL_SEL bit is modified to change

the group of current channels being measured, the new result is

available in 125 μs (8 kHz).

ZERO-CROSSING DETECTION

Zero-Crossing Detection

The ADE7816 has a zero-crossing (ZX) detection circuit on the

voltage and current channels. Zero-crossing detection allows

measurements to be synchronized to the frequency of the

incoming waveforms.

The zero-crossing events are filtered internally by an LPF. The

LPF is intended to eliminate all harmonics of 50 Hz and 60 Hz

systems, and to help identify the zero-crossing events on the

fundamental components of both current and voltage channels.

The digital filter has a pole at 80 Hz and is clocked at 256 kHz.

As a result, there is a phase lag between the analog input signal

and the output of the LPF. The error in ZX detection is 0.0703°

for 50 Hz systems and 0.0843° for 60 Hz systems. The phase lag

response of the LPF results in a time delay of approximately

31.4° or 1.74 ms (at 50 Hz) between its input and output. The

overall delay between the zero crossing on the analog inputs and

the ZX detection that is obtained after LPF1 is about 39.6° or

2.2 ms (at 50 Hz). Figure 33 shows how the zero-crossing signal

is detected.

To provide further protection from noise, input signals to the

voltage channel with an amplitude of <10% of full scale do not

generate zero-crossing events at all. The ZX detection circuit of

the current channels is active for all input signals, independent

of their amplitudes.

IxGAIN OR

VGAIN

REFERENCE

HPF

PGA

ADC

IA, IB, IC,

ID, IE, IF, OR V

DETECTION

LPF_ZX

IA, IB, IC,

ID, IE, IF, OR V

39.6° OR 2.2ms @ 50Hz

0.855

LPF_ZX OUTPUT

Figure 33. Zero-Crossing Detection

ADE7816 数据表(PDF) 26 Page - Analog Devices

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