ADE9000 Technical Reference Manual
UG-1098
Rev. 0 | Page 25 of 86
The zero-crossing threshold, ZXTHRSH, can be calculated
from the following equation:
8
2
32
)
_
(
)
_
(
×
×
×
=
X
N
ATTENUATIO
LPF1
Scale
Full
at
PCF
V
ZXTHRSH
where:
V_PCF
at full scale is ±74,532,013 (decimal).
X
is the dynamic range that the zero-crossing must be blocked
below.
LPF1_ATTENUATION
is 0.86 at 50 Hz and 0.81 at 60 Hz, the
gain attenuation of the LPF1 filter.
For example, to prevent signals 100 times lower than full scale
from generating a ZX output, set ZXTHRSH to 78 (decimal):
d
78
2
32
100
)
86
.
0
(
)
013
,
532
,
74
(
8
=
×
×
×
=
ZXTHRSH
Additionally, to prevent false zero-crossings, after a ZX is
generated, 1 ms must elapse before the next ZX can be output.
Combined Voltage Zero-Crossing
Phase A, Phase B, and Phase C voltage channel signals are
combined to generate one zero-crossing signal, ZX_COMB, that
is stable even if one or more phases drops out.
The input to the zero-crossing detection is (VA + VB − VC)/2
with the signal chain corresponding to Figure 28. As described
in the Applying the ADE9000 to Different Metering
Configurations section, the
can be used to meter
different polyphase configurations. The VCONSEL[2:0] bits in
the ACCMODE register are used to indicate this selection. If
VCONSEL[2:0] is not equal to 0, the VB component in the
combined zero-crossing circuit is set to zero.
The same precautions are used to prevent noise from generating
zero-crossing interrupts on this output. As described in the
Zero-Crossing Detection section, signals below the ZXTHRSH
threshold do not generate ZXCOMB outputs, and a minimum
of 1 ms is required between ZXCOMB generation.
HPF
ZX DETECTION,
LINE PERIOD
CALCULATION
PHASE
COMP
HPFDIS
HPFDIS
HPFDIS
ZX_SRC_SEL
AV_PCF
PHASE A
PHASE B
PHASE C
(VA + VB – VC)/2
HPF
ZX_SRC_SEL
BV_PCF
HPF
PHASE
COMP
ZX_SRC_SEL
CV_PCF
÷2
VCONSEL[2:0]
0
PHASE
COMP
15523-
028
LPF1
Figure 28. Combined Zero-Crossing Detection