Analog Devices ADE9000 Technical Reference Manual page 25

ADE9000 Technical Reference Manual
The zero-crossing threshold, ZXTHRSH, can be calculated
from the following equation:
=
ZXTHRSH
( V _ PCF at Full Scale
X
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):
=
ZXTHRSH
×
( 74 , 532 , 013 ) . 0 ( 86 )
× × 8
100 32 2
Additionally, to prevent false zero-crossings, after a ZX is
generated, 1 ms must elapse before the next ZX can be output.
HPFDIS
PHASE A
HPF
HPFDIS
PHASE B
HPF
HPFDIS
PHASE C
HPF
×
) ( LPF1 _ ATTENUATIO N
× × 8
32 2
=
78 d
PHASE
COMP
AV_PCF
PHASE
COMP
BV_PCF
PHASE
COMP
CV_PCF
Figure 28. Combined Zero-Crossing Detection
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
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.
ZX_SRC_SEL
ZX_SRC_SEL
0
VCONSEL[2:0]
ZX_SRC_SEL
Rev. 0 | Page 25 of 86
ADE9000 can be used to meter
(VA + VB – VC)/2
ZX DETECTION,
÷2
LINE PERIOD
LPF1 CALCULATION
UG-1098