ADE7761BARS-REF AD [Analog Devices], ADE7761BARS-REF Datasheet - Page 18

• Manufacturer Part Number: ADE7761BARS-REF
• Description: Energy Metering IC with On-Chip Fault and Missing Neutral Detection
• Manufacturer: AD [Analog Devices]

ADE7761B
Fault with Active Input Greater Than Inactive Input
If V
and the voltage signal on V
of V
are filtered and averaged to prevent false triggering of this logic
output. As a consequence of the filtering, there is a time delay of
approximately 3 sec on the Logic Output FAULT after the fault
event. The FAULT logic output is independent of any activity on
the F1 or F2 outputs. Figure 28 shows one condition under
which FAULT becomes active. Because V
and it is still greater than V
is, no swap to the V
Fault with Inactive Input Greater Than Active Input
Figure 29 illustrates another fault condition. If the difference
between V
is, being used for billing), becomes greater than 6.25% of V
the FAULT indicator becomes active and a swap over to the V
input occurs. The Analog Input V
Again, a time constant of about 3 sec is associated with this swap.
V
than V
becomes greater than 6.25% of V
cator becomes inactive as soon as V
threshold eliminates potential chatter between V
0V
0V
1A
Figure 28. Fault Conditions for Active Input Greater Than Inactive Input
Figure 29. Fault Conditions for Inactive Input Greater Than Active Input
1A
does not swap back to the active channel until V
1A
V
V
<0
FAULT
1B
1A
, the fault indicator becomes active. Both analog inputs
is the active current input (that is, being used for billing),
FAULT + SWAP
1B
<0
6.25% OF ACTIVE INPUT
6.25% OF INACTIVE INPUT
< 93.75% OF V
< 93.75% OF V
V
V
, and the difference between V
V
V
1A
1A
1B
1B
1B
, the inactive input, and V
AGND
AGND
1A
1B
1B
input occurs. V
V
V
>0
V
V
1A
1B
1A
1B
>0
1B
1B
V
V
V
V
V
V
, billing is maintained on V
1A
1N
1B
1A
1N
1B
(inactive input) falls below 93.75%
ACTIVE POINT – INACTIVE INPUT
ACTIVE POINT – INACTIVE INPUT
1A
1A
1B
. However, the FAULT indi-
becomes the active input.
is within 6.25% of V
1A
1A
1A
A
B
A
B
remains the active input.
, the active input (that
1A
and V
COMPARE
COMPARE
is the active input
FILTER
FILTER
AND
AND
1B
1A
, in this order,
and V
FAULT
TO
MULTIPLIER
FAULT
TO
MULTIPLIER
1A
is greater
1B
1A
. This
1B
; that
.
1B
Rev. 0 | Page 18 of 24
,
1B
Calibration Concerns
Typically, when a meter is being calibrated, the voltage and current
circuits are separated, as shown in Figure 30. This means that
current passes through only the phase or neutral circuit. Figure 30
shows current being passed through the phase circuit. This is
the preferred option because the ADE7761B starts billing on the
input V
V
the FAULT indicator comes on under these conditions. However,
this does not affect the accuracy of the calibration and can be
used as a means to test the functionality of the fault detection.
If the neutral circuit is chosen for the current circuit in the
arrangement shown in Figure 30, this may have implications for
the calibration accuracy. The ADE7761B powers up with the
V
in the phase circuit, the signal on V
to be flagged and the active input to be swapped to V
The meter can be calibrated in this mode, but the phase and
neutral CTs may differ slightly. Because under no-fault conditions
all billing is carried out using the phase CT, the meter should be
calibrated using the phase circuit. Of course, both phase and
neutral circuits can be calibrated.
MISSING NEUTRAL MODE
The ADE7761B integrates a novel fault detection scheme that
warns and allows the ADE7761B to continue to bill in case a
meter is connected to only one wire (see Figure 31). For correct
operation of the ADE7761B in this mode, the V
ADE7761B must be maintained within the specified range
(5 V ± 5%). The missing neutral detection algorithm is designed
to work over a line frequency of 45 Hz to 55 Hz.
1
CURRENT
RB + VR = RF.
1A
1A
TEST
in Figure 30. Because there is no current in the neutral circuit,
input active as normal. However, because there is no current
1A
on power-up. The Phase Circuit CT is connected to
IB
IB
Figure 30. Conditions for Calibration of Channel B
240V rms
V
AGND
RA
1
RB
VR
1
1
CT
CT
RB
RB
C
F
R
0V
1A
V
F
1A
C
R
R
is zero. This causes a fault
T
F
F
V
V
2N
2P
C
C
F
F
DD
V
V
V
1A
1N
1B
pin of the
1B
(neutral).