Analog Devices ADE9000, Техническое справочное руководство

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ADE9000 Technical Reference Manual UG-1098
Rev. 0 | Page 27 of 86
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 on is not received after ZXTOUT 8 ksps
clocks, the corresponding ZXTOx bit in the STATUS1 register is
set. For example, if ZXTOUT is equal to 8000, if a zero-crossing is
not then received on Phase A for 8000/8 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/8000 = 8.19 sec.
Line Period Calculation
The ADE9000 line period measurement is done 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 positive to negative zero-crossing to calculate the exact
zero-crossing point using linear interpolation. This information
is used to precisely calculate the line period, which is stored in
the xPERIOD register.
4.3ms AT 50Hz
Ix,Vx
0.86
0V
LPF1 OUTPUT
POS2 POS1 POS2
x
x
x
x
POS1
15523-
030
Figure 30. Line Period Calculation using Zero-Crossing Detection and
Linear Interpolation
The line period, T
L
, can be calculated from the xPERIOD
register according to the following equation:
(sec)
2 8000
1
16
×
+
=
xPERIOD
T
L
Similarly, the line frequency can be calculated from the
xPERIOD register, using the following equation:
) Hz (
1
2 8000
16
+
×
=
xPERIOD
f
L
With a 50 Hz input, the xPERIOD register is 0x00A0_0000,
10485760 (decimal), and with 60 Hz, it is 0x0085_5554,
8738132 (decimal).
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 be coerced to
correspond to 50 Hz or 60 Hz, according to the setting of the
SELFREQ bit in the ACCMODE register. With SELFREQ equal
to 0 for a 50 Hz network, the xPERIOD register is coerced to
0x00A0_0000. If SELFREQ is 1, indicating a 60 Hz network, the
xPERIOD register is coerced to 0x0085_5554.
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.
The line period calculation is used for the resampling
measurement. Select which phase voltage line period is used as
the basis for resampling calculation using the LP_SEL[1:0] bits
in the ZX_LP_SEL register, or select a user configured value
written in USER_PERIOD using the UPERIOD_SEL bit in the
CONFIG2 register.
The user period selection can help 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 or calculating a fast rms measurement.
USER_PERIOD[31:0] has the same scaling as the xPERIOD
registers. Write USER_PERIOD[31:0] to 0x00A0_0000 for
50 Hz and 0x0085_5554 for 60 Hz.
Angle Measurement
The ADE9000 measures the time between zero-crossings on
each phase. This measurement helps to determine if the system
is balanced properly or to figure out if there was an installation
error. The user can check if the phase angles correspond to the
ones in the phasor diagrams in the Applying the ADE9000 to
Different Metering Configurations section.
The times between positive to negative zero-crossings are
measured using a CLKIN/24 = 24.576/24 = 1024 kHz clock.
The time between the zero-crossing on Phase A and Phase B is
stored in the ANGL_VA_VB register. The resolution of the
ANGLx_x2x register is (1/(1024 × 1000))/20 ms × 360° =
0.017578125° at 50 Hz.
The time between the zero-crossing on Phase B and C is stored
in the ANGL_VB_VC register, and the time in between the
zero-crossings on Phase A and C is stored in the
ANGL_VA_VC register, as shown in Figure 31.
ANGL_VA_VB ANGL_VB_VC
ANGL_VA_VC
15523-
031
Figure 31. Voltage to Voltage Phase Angle
The angle in degrees can be calculated from the following
equation with a 50 Hz line period:
Angle (degrees) = ANGL_VA_VB × 0.017578125/LSB
For a 4-wire wye configuration, the expected ANGL_VA_VB
and ANGL_VB_VC is 120°/0.017578125 = 3413 (decimal). Note
that the expected ANGL_VA_VC from the Phase A voltage to
Phase C voltage is 240°/0.017578125 = 13653 (decimal), which
corresponds to a 120° angle between Phase C and Phase A.
The current to current zero-crossings are also measured. This
measurement is done similarly to the voltage to voltage phase
angle described previously, except the current channel zero-