ADE7761
V
R
1A
F
Important Note for Billing of Active Energy
CT
IB
The ADE7761 provides pulse outputs—CF, F1, and F2—
intended to be used for the billing of active energy. Pulses are
generated at these outputs in two different situations.
RB
RB
C
240V RMS
POWER
GENERATOR
F
V1A
0V
V
1N
Case 1: When the analog input V2P – V2N complies with the
conditions described in Figure 32, CF, F1, and F2 frequencies
are proportional to active power and can be used to bill active
energy.
C
F
CT
RA*
R
V
1B
F
LOAD
C
F
F
RB*
VR*
Case 2: When the analog input V2P – V2N does not comply with
the conditions described in Figure 32, the ADE7761 does not
measure active energy, but a quantity proportional to kAh. This
quantity is used to generate pulses on the same CF, F1, and F2.
This situation is indicated when the FAULT pin is high.
V
V
2P
R
2N
C
T
*RB + VR = RF
Figure 29. Missing Neutral System Diagram
Analog Devices Inc. cautions users of the ADE7761:
The ADE7761 detects a missing neutral condition by continu-
ously monitoring the voltage channel input (V2P–V2N). The
FAULT pin is held high when a missing neutral condition is
detected. In this mode, the ADE7761 continues to bill the
energy based on the signal level on the current channel (see
Figure 30). The billing rate or frequency outputs can be adjusted
by changing the dc level on the MISCAL pin.
•
•
Billing active energy in Case 1 is consistent with the
understanding of the quantity represented by pulses on
CF, F1, and F2 outputs (watt-hour).
Billing active energy while the ADE7761 is in Case 2 must
be decided knowing that the entity measured by the
ADE7761 in this case is ampere-hour and not watt-hour.
Users should be aware of this limitation and decide if the
ADE7761 is appropriate for their application.
V
1A
ADC
A > B
V
V
1N
1B
HPF
Missing Neutral Detection
ADC
ADC
ZERO
CROSSING
DETECTION
B > A
B <> A
The ADE7761 continuously monitors the voltage input and
detects a missing neutral condition when the voltage input peak
value is smaller than 9% of the analog full scale or when no zero
crossings are detected on this input (see Figure 31).
LPF
MISSING NEUTRAL
GAIN ADJUSMENT
MISCAL
DIGITAL-
TO-
FREQUENCY
CONVERTERS
V
MISSING
2P
NEUTRAL
FILTER AND
THRESHOLD
V2
ADC
F1 F2
CF
V
2N
AGND
Figure 30. Energy Calculation in Missing Neutral Mode
|V2|
PEAK
< 9% OF FULL SCALE
OR
NO ZERO-CROSSING ON V2
V
–V
2P 2N
V
–V
2P 2N
V
–V
2P 2N
FS
FS
FS
9% OF FS
0V
0V
0V
Figure 31. Missing Neutral Detection
Rev. A | Page 21 of 28
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