ade7761a Analog Devices, Inc., ade7761a Datasheet - Page 19

• Manufacturer Part Number: ade7761a
• Description: Energy Metering Ic With On-chip Fault And Missing Neutral Detection
• Manufacturer: Analog Devices, Inc.

The ADE7761A detects a missing neutral condition by
continuously monitoring the voltage channel input (V
The FAULT pin is held high when a missing neutral condition is
detected. In this mode, the ADE7761A 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.
Important Note for Billing of Active Energy
The ADE7761A 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.
Case 1 : When the analog input V
conditions described in Figure 34, CF, F1, and F2 frequencies
are proportional to active power and can be used to bill active
energy.
Case 2 : When the analog input V
the conditions described in Figure 34, the ADE7761A 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
V
MISCAL
GENERATOR
1
1A
1N
1B
RB + VR = RF.
244V rms
POWER
LOAD
Figure 32. Energy Calculation in Missing Neutral Mode
Figure 31. Missing Neutral System Diagram
ADC
ADC
ADC
IB
A > B
B > A
B <> A
GAIN ADJUSMTENT
MISSING NEUTRAL
HPF
RA
RB
VR
2P
2P
CT
CT
DETECTION
CROSSING
1
1
1
– V
– V
ZERO
RB
RB
2N
2N
R
C
F
complies with the
does not comply with
C
F
T
0V
V
R
R
1A
F
F
V
V
2N
2P
C
C
V
V
V
F
F
CONVERTERS
CF F1 F2
1A
1N
1B
FREQUENCY
DIGITAL-TO-
2P
LPF
− V
2N
Rev. 0 | Page 19 of 24
).
Analog Devices, Inc. cautions users of the ADE7761A about the
following:
• Billing active energy in Case 1 is consistent with the
• Billing active energy while the ADE7761A is in Case 2 must
Missing Neutral Detection
The ADE7761A 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).
The ADE7761A 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operation when both conditions are no longer valid, that is, a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).
|V2|
AGND
AGND
9% OF FS
understanding of the quantity represented by pulses on CF,
F1, and F2 outputs (watt-hour).
be decided knowing that the entity measured by the
ADE7761A in this case is ampere-hour and not watt-hour.
Users should be aware of this limitation and decide if the
ADE7761A is appropriate for their application.
PEAK
Figure 34. Return to Normal Mode after Missing Neutral Detection
V2
V2
V
0V
FS
2P
< 9% OF FULL SCALE
– V
V
V
V
V
2P
2N
2P
2N
2N
Figure 33. Missing Neutral Detection
|V2|
+9% OF FS
–9% OF FS
ZERO CROSSING ON V2
PEAK
> 9% OF FULL SCALE
V
V
0V
FS
FS
2P
2P
OR
AND
– V
– V
ADC
ADC
2N
2N
NO ZERO CROSSING ON V2
THRESHOLD
THRESHOLD
FILTER AND
FILTER AND
V
0V
FS
2P
– V
ADE7761A
2N
MISSING
NEUTRAL
MISSING
NEUTRAL