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參數(shù)資料
| 型號： | AD7751 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Energy Metering IC with On-Chip Fault Detection(高精度容錯電子能量測量芯片) |
| 中文描述： | 電能計量IC片故障檢測（高精度容錯電子能量測量芯片） |
| 文件頁數(shù)： | 13/16頁 |
| 文件大?。?/td> | 287K |
| 代理商： | AD7751 |
PRELIMINARY TECHNICAL DATA
AD7751
13
PRELIM B1 10/98
fluctuations—see Signal Processing Block in figuren 5.
TABLE IV
SCF
S1
S0
F
1-4
(Hz)
CF max for ac signals (Hz)
1
0
1
0
1
0
1
0
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0.43
0.43
0.85
0.85
1.7
1.7
3.41
3.41
128 x Freq = 10.88
64 x Freq = 5.44
64 x Freq = 10.88
32 x Freq = 5.44
32 x Freq = 10.88
16 x Freq = 5.44
16 x Freq = 10.88
8 x Freq = 5.44
FAULT DETECTION
The AD7751 incorporates a novel fault detection scheme which
both warns of fault conditions and allows the AD7751 to
continue accurate billing during a fault event. The AD7751
does this by continuously monitoring both the phase and
neutral (return) currents. A fault is indicated when these
currents differ by more than 12.5%. However even during a
fault the output pulse rate on F1 and F2 is generated using the
larger to the two currents. Because the AD7751 in fact looks
for a difference between the voltage signals on V1A and V1B, it
is important that both current transducers are closely matched.
On power up the output pulse rate of the AD7751 is propor-
tional to the product of the voltage signals on V1A and Channel
2. If there is a difference of greater than 12.5% between V1A
and V1B on power up then the fault indicator (FAULT) will go
active after about one second. In addition if V1B is greater than
V1A then the AD7751 will select V1B as the input.
Fault with Active Input greater than Inactive Input
If V1A is the active current input (i.e., is being used for billing)
and the voltage signal on V1B (inactive input) falls by more
than 12.5% of V1A then the fault indicator will go active. Both
analog inputs are filtered and averaged to prevent false trigger-
ing of this logic output. As a consequence of the filtering there
is a time delay of approximately one second on the logic output
FAULT after the fault event. The FAULT logic output is
independent of any activity on outputs F1 or F2. Figure 10
below illustrates one condition under which FAULT becomes
active. Since V1A is the active input and V1A is still greater
than V1B no swap to V1B input will occur. V1A remains the
active input.
+
-
V1A
V1N
V1A
0V
V1A
AGND
+
-
V1B
V1B
V1B
A
B
FAULT
TO
MULTIPLIER
FILTER
&
COMPARE
V1B < 87.5% of V1A
Figure 10. Fault conditions for inactive input less than active
input
Fault with V1B greater than V1A
Figure 11 illustrates another fault condition. If V1A is the
active input (i.e., is being used for billing) and the voltage
signal on V1B (inactive input) becomes greater than 114% of
V1A then the FAULT indicator goes active and there is also a
swap over to the V1B input. The analog input V1B has now
become the active input. Again there is a time constant of
about 1 second associated with this swap. V1A will not swap
back to being the active channel until V1A becomes greater
than 114% of V1B. However the FAULT indicator will become
inactive as soon as V1A is within 12.5% of V1B.
+
-
V1A
V1N
V1B
0V
V1A
AGND
+
-
V1B
V1B
V1A
A
B
FAULT
TO
MULTIPLIER
FILTER
CO&
V1A < 87.5% of V1B
or
V1B > 114% of V1A
Figure 11. Fault conditions for inactive input greater than
active input
Calibration Concerns
Typically when a meter is being calibrated the voltage and
current circuits are separated as shown in the figure 7. This
means that current will only pass through the Phase or Neutral
circuit. Figure 12 shows current being passed through the
Phase circuit. This is the preferred option since the AD7751
starts billing on the input V1A on power up. The Phase circuit
CT is connected to V1A in the diagram. Since there is no
current in the Neutral circuit the FAULT indicator will come
on under these conditions. However this in no way affects the
accuracy of the calibration and can be used as a means to test
the functionality of the fault detection.
+
-
V1A
V1N
AGND
+
-
V1B
CT
CT
Rb
Rb
Rf
Rf
Cf
Cf
Ib
+
-
V2P
V2N
Ra*
Rf
Cf
Cf
Rb*
*Ra // Rb = Rf
Ib
V
240V rms
Test
Current
V1A
0V
Figure 12. Fault conditions for inactive input greater than
active input
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD7751AAN | 制造商:Analog Devices 功能描述: 制造商:Rochester Electronics LLC 功能描述:PRODUCT TO FREQUENCY CONV - Bulk |
| AD7751AAN-REF | 制造商:Analog Devices 功能描述: |
| AD7751AARS | 制造商:Rochester Electronics LLC 功能描述:PRODUCT TO FREQUENCY CONV - Bulk |
| AD7751ABRS | 制造商:AD 制造商全稱:Analog Devices 功能描述:Energy Metering IC With On-Chip Fault Detection |
| AD7751AN | 制造商:Rochester Electronics LLC 功能描述:PRODUCT TO FREQUENCY CONV - Bulk |
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