ADE7761B
V
R
V
1A
F
Analog Devices cautions users of the ADE7761B about the
following:
CT
IB
RB
RB
C
244V rms
POWER
GENERATOR
F
• Billing active energy in Case 1 is consistent with the under-
standing of the quantity represented by pulses on the CF, F1,
and F2 outputs (watthour).
1A
V
1N
0V
C
F
• Billing active energy while the ADE7761B is in Case 2 must
be decided knowing that the entity measured by the ADE7761B
in this case is ampere-hour and not watthour. Users should
be aware of this limitation and decide if the ADE7761B is
appropriate for their application.
CT
1
R
V
1B
F
LOAD
RA
C
F
F
1
1
RB
V
V
2P
VR
R
2N
Missing Neutral Detection
C
F
The ADE7761B 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 33).
1
RB + VR = RF.
Figure 31. Missing Neutral System Diagram
The ADE7761B 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 ADE7761B continues to bill the energy
based on the signal level on the current channel (see Figure 32).
The billing rate or frequency outputs can be adjusted by changing
the dc level on the MISCAL pin.
V
MISSING
2P
NEUTRAL
FILTER AND
THRESHOLD
V2
ADC
V
2N
AGND
|V2|
< 9% OF FULL SCALE
OR
NO ZERO CROSSING ON V2
PEAK
V
V
V
1A
1N
1B
ADC
V
– V
2N
V
– V
2N
V – V
2P 2N
2P
2P
A > B
HPF
FS
FS
FS
ADC
ZERO
CROSSING
DETECTION
B > A
A ≠ B
9% OF FS
0V
0V
0V
LPF
MISSING NEUTRAL
GAIN ADJUSMTENT
MISCAL
ADC
DIGITAL-TO-
FREQUENCY
CONVERTERS
Figure 33. Missing Neutral Detection
The ADE7761B leaves the missing neutral mode for normal
operation when both conditions are no longer valid; that is,
a voltage peak value of greater than 9% of full scale and zero
crossing on the voltage channel is detected (see Figure 34).
F1 F2
CF
Figure 32. Energy Calculation in Missing Neutral Mode
Important Note for Billing of Active Energy
V
MISSING
2P
NEUTRAL
The ADE7761B provides pulse outputs, CF, F1, and F2, that are
intended to be used for the billing of active energy. Pulses are
generated at these outputs in two different situations.
FILTER AND
THRESHOLD
V2
ADC
V
2N
AGND
Case 1
|V2|
PEAK
> 9% OF FULL SCALE
AND
When the analog input V2P − V2N complies with the conditions
described in Figure 34, the CF, F1, and F2 frequencies are propor-
tional to active power and can be used to bill active energy.
ZERO CROSSING ON V2
V
– V
2N
2P
FS
Case 2
+9% OF FS
–9% OF FS
When the analog input V2P − V2N does not comply with the
conditions described in Figure 34, the ADE7761B 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.
Figure 34. Return to Normal Mode After Missing Neutral Detection
Rev. 0 | Page 19 of 24
ADI [ ADI ]
