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ADE7761A
Fault with Active Input Greater than Inactive Input
If V 1A is the active current input (that is, being used for billing),
and the voltage signal on V 1B (inactive input) falls below 93.75%
of V 1A , the fault indicator becomes active. Both analog inputs
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
outputs F1 or F2. Figure 28 shows one condition under which
FAULT becomes active. Because V 1A is the active input and it is
still greater than V 1B , billing is maintained on V 1A , that is, no
swap to the V 1B input occurs. V 1A remains the active input.
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 ADE7761A
starts billing on the input V 1A on power-up. The phase circuit
CT is connected to V 1A in Figure 30. Because there is no current
in the neutral circuit, 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.
V 1A
V 1A
FILTER
AND
FAULT
IB
CT
R F
V 1A
V 1B
A
COMPARE
0V
AGND
V 1A
V 1B
V 1N
B
TO
MULTIPLIER
AGND
RB
V 1A
C F
V 1N
V 1B < 93.75% OF V 1A
FAULT
<0
>0
6.25% OF ACTIVE INPUT
V 1B
ACTIVE POINT – INACTIVE INPUT
TEST
CURRENT
IB
RA 1
RB 1
VR 1
CT
RB
C F
0V
R F
V 2P
C F
V 1B
Figure 28. Fault Conditions for Active Input Greater than Inactive Input
V
R F
C T
V 2N
Fault with Inactive Input Greater than Active Input
Figure 29 illustrates another fault condition. If the difference
between V 1B , the inactive input, and V 1A , the active input (that
is, being used for billing), becomes greater than 6.25% of V 1B ,
the FAULT indicator becomes active and a swap over to the V 1B
input occurs. The analog input V 1B becomes the active input.
Again, a time constant of about 3 sec is associated with this
swap. V 1A does not swap back to the active channel until V 1A is
greater than V 1B and the difference between V 1A and V 1B —in
this order—becomes greater than 6.25% of V 1A . However, the
FAULT indicator becomes inactive as soon as V 1A is within
6.25% of V 1B . This threshold eliminates potential chatter
between V 1A and V 1B .
240V rms
1 RB + VR = RF.
Figure 30. Conditions for Calibration of Channel B
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 ADE7761A powers up with the
V 1A input active as normal. However, because there is no
current in the phase circuit, the signal on V 1A is zero. This
causes a fault to be flagged and the active input to be swapped
to V 1B (neutral). 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
V 1A
V 1B
V 1A
A
FILTER
AND
COMPARE
FAULT
course, both phase and neutral circuits can be calibrated.
MISSING NEUTRAL MODE
0V
AGND
V 1A
V 1B
V 1N
B
TO
MULTIPLIER
The ADE7761A integrates a novel fault detection that warns
and allows the ADE7761A to continue to bill in case a meter is
connected to only one wire (see Figure 31). For correct
V 1A < 93.75% OF V 1B
FAULT + SWAP
<0
V 1B
>0
ACTIVE POINT – INACTIVE INPUT
operation of the ADE7761A in this mode, the V DD pin of the
ADE7761A 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.
6.25% OF INACTIVE INPUT
Figure 29. Fault Conditions for Inactive Input Greater than Active Input
Rev. 0 | Page 18 of 24
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相关代理商/技术参数
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ADE7761ARSRL 制造商:AD 制造商全称:Analog Devices 功能描述:Energy Metering IC with On-Chip Fault and Missing Neutral Detection
ADE7761B 制造商:AD 制造商全称:Analog Devices 功能描述:Energy Metering IC with On-Chip Fault and Missing Neutral Detection
ADE7761BARS 制造商:Rochester Electronics LLC 功能描述: 制造商:Analog Devices 功能描述:
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ADE7761BARS-RL 制造商:AD 制造商全称:Analog Devices 功能描述:Energy Metering IC with On-Chip Fault and Missing Neutral Detection
ADE7761BARSZ 功能描述:IC ENERGY METERING 1PHASE 20SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 能量测量 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:*