ADE9078ACPZ datasheet(52/108 Pages) AD

52 / 108 page

Data Sheet

ADE9078

Rev. 0 | Page 51 of 107

Functions Using

Zero Crossing

ZX Transitions

Used

Corresponding

STATUS1 Bits

Selecting Which Phase to

Use for Measurement

Effect if ZX Does Not Occur

Resampling

None

Not applicable

LP_SEL selects the phase

voltage line period used as

the basis for resampling

calculation

If the line period used for resampling is invalid

because zero crossings are not detected or

the calculation results in something outside

a 40 Hz to 70 Hz range, the line period used

for resampling is coerced to the default line

period of 0x00500000 if SELFREQ = 0 for a

50 Hz network, or 0x0042AAAB if SELFREQ = 1

for a 60 Hz network.

Angle

Measurements

Negative to

positive

Not applicable

The register does not update, keeps last

value.

ZX Output on the

CF3/ZX Pin

Negative to

positive and

positive to

negative

Not applicable

ZX_SEL selects the zero-

crossing output used for line

cycle energy accumulation

and the ZX output pin

The ZX output remains at the current state,

high or low.

Zero-Crossing Timeout

The zero-crossing timeout feature alerts the user if a zero-crossing

event is not generated after a user configured amount of time. If

a zero crossing event is not received after ZXTOUT/4 kSPS clocks,

the corresponding ZXTOx bit in the STATUS1 register is set.

For example, if ZXTOUT is equal to 4000, if a zero crossing is

not received on Phase A for 4000/4 kSPS = 1 sec, the ZXTOA bit

is set in the STATUS1 register. The maximum value that can be

written to the ZXTOUT register is 0xFFFF/4000 = 16.38 sec.

Line Period Calculation

The ADE9078 line period measurement is performed by taking

the values low-pass filtered by LPF1 as described in the Zero-

Crossing Detection section and then using the two values near

the negative to positive zero crossing (POS1 and POS2) to calculate

the exact zero-crossing point using linear interpolation. Use this

information to calculate the line period precisely, which is

stored in the xPERIOD register.

4.3ms AT 50Hz

Ix,Vx

0.86

LPF1 OUTPUT

POS2

POS1 POS2

POS1

Figure 73. Line Period Calculation Using Zero-Crossing Detection and Linear

Interpolation

The line period, tL, can be calculated from the xPERIOD

(sec)

4000







xPERIOD

Similarly, the line frequency can be calculated from the

xPERIOD register using the following equation:

(Hz)

4000







xPERIOD

With a 50 Hz input, the xPERIOD register is 0x0050 0000,

5242880d, and with a 60 Hz input, it is 0x0042 AAAA = 4369066d.

If the calculated period value is outside the range of 40 Hz to

70 Hz, or if the negative to positive zero crossings for that phase

are not detected, the xPERIOD register is coerced to correspond

to 50 Hz or 60 Hz, according to the setting of the SELFREQ bit

in the ACCMODE register. With SELFREQ = 0 for a 50 Hz

network, xPERIOD register is coerced to 0x0050 0000. If

SELFREQ = 1, indicating a 60 Hz network, the xPERIOD

The line period is calculated for the Phase A, Phase B, and

Phase C voltages and the combined voltage signal, as described

in the Combined Voltage Zero Crossing section, and stored in

the APERIOD, BPERIOD, CPERIOD, and COM_PERIOD,

registers respectively.

Select the phase voltage line period to use as the basis for the

resampling calculation using the LP_SEL bits in the ZX_LP_SEL

using the UPERIOD_SEL bit in the CONFIG2 register, as

shown in Figure 74.

LP_SEL

COM_PERIOD

CPERIOD

BPERIOD

APERIOD

RESAMPLING1

1NOT AVAILABLE IN ADE9078 PSM1.

USER_PERIOD

UPERIOD_SEL

WAVEFORM

BUFFER1

SINC4 OUTPUT

SINC4 + IIR LPF OUTPUT

xI_PCF, xV_PCF

ADE9078

WF_CAP_SEL

WF_SRC

Figure 74. Line Period Selection for Resampling

The user period selection is helpful in applications where the

user has another algorithm to determine the line frequency or if

it is preferred to always assume a certain line frequency when

resampling. USER_PERIOD[31:0] has the same scaling as the

xPERIOD registers. Write USER_PERIOD[31:0] to 0x00500000

for 50 Hz and 0x0042AAAB for 60 Hz.

Angle Measurement

The ADE9078 measures the time between zero crossings on

each phase. This measurement determines if the system is

balanced properly or to determine if there was an installation

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