ADE7761A View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADE7761A' PDF : 24 Pages View PDF
IB
244V rms
POWER
GENERATOR
RF
V1A
CT
RB
V1A
CF
0V
RB
V1N
CF
LOAD
CT
RA1
RB1
VR1
RF
V1B
CF
V2P
RF
V2N
CT
1RB + VR = RF.
Figure 31. Missing Neutral System Diagram
The ADE7761A detects a missing neutral condition by
continuously monitoring the voltage channel input (V2P − V2N).
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.
V1A
V1N
V1B
MISCAL
ADC
A>B
HPF
ADC
B>A
B <> A
ZERO
CROSSING
DETECTION
ADC
MISSING NEUTRAL
GAIN ADJUSMTENT
LPF
DIGITAL-TO-
FREQUENC Y
CONVERTERS
CF F1 F2
Figure 32. Energy Calculation in Missing Neutral Mode
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 V2P – V2N complies with the
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 V2P – V2N does not comply with
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.
ADE7761A
Analog Devices, Inc. cautions users of the ADE7761A about the
following:
• 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 ADE7761A is in Case 2 must
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.
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).
V2P
V2
V2N
AGND
ADC
MISSING
NEUTRAL
FILTER AND
THRESHOLD
|V2|PEAK < 9% OF FULL SCALE OR NO ZERO CROSSING ON V2
V2P – V2N
FS
V2P – V2N
FS
V2P – V2N
FS
9% OF FS
0V
0V
0V
Figure 33. Missing Neutral Detection
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).
V2P
V2
V2N
AGND
ADC
MISSING
NEUTRAL
FILTER AND
THRESHOLD
|V2|PEAK > 9% OF FULL SCALE
AND
ZERO CROSSING ON V2
V2P – V2N
FS
+9% OF FS
–9% OF FS
Figure 34. Return to Normal Mode after Missing Neutral Detection
Rev. 0 | Page 19 of 24
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