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參數(shù)資料
| 型號(hào)： | EVAL-AD7751EB |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Energy Metering IC With On-Chip Fault Detection |
| 中文描述： | 電能計(jì)量IC，帶有片上故障檢測(cè) |
| 文件頁(yè)數(shù)： | 11/16頁(yè) |
| 文件大?。?/td> | 249K |
| 代理商： | EVAL-AD7751EB |
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REV. A
AD7751
–11–
Using Equations 2 and 3, the real-power
P
can be expressed in
terms of its fundamental real power (
P
1
) and harmonic real
power (
P
H
).
P
=
P
1
+
P
H
where:
P
φ
V
α
I
β
1
1
1
1
1
1
=
=
×
–
cos( )
(4)
and
P
V
1
I
H
h
h
h
h
h
h
h
= ∑
×
×
=
≠
∞
cos(
)
–
φ
φ
α
β
(5)
As can be seen from Equation 5 above, a harmonic real-power
component is generated for every harmonic, provided that har-
monic is present in both the voltage and current waveforms.
The power factor calculation has previously been shown to be
accurate in the case of a pure sinusoid, therefore the harmonic
real power must also correctly account for power factor since it
is made up of a series of pure sinusoids.
Note that the input bandwidth of the analog inputs is 14 kHz
with a master clock frequency of 3.5795 MHz.
ANALOG INPUTS
Channel V2 (Voltage Channel)
The output of the line voltage transducer is connected to the
AD7751 at this analog input. Channel V2 is a fully differential
voltage input. The maximum peak differential signal on Chan-
nel 2 is
±
660 mV. Figure 4 illustrates the maximum signal levels
that can be connected to the AD7751 Channel 2.
DIFFERENTIAL INPUT
600mV MAX PEAK
+600mV
AGND
V
CM
V2
V2P
V
CM
–
600mV
COMMON-MODE
100mV MAX
V2N
V2
Figure 4. Maximum Signal Levels, Channel 2
Channel 2 must be driven from a common-mode voltage, i.e.,
the differential voltage signal on the input must be referenced to
a common mode (usually AGND). The analog inputs of the
AD7751 can be driven with common-mode voltages of up to
100 mV with respect to AGND. However, best results are
achieved using a common mode equal to AGND.
Channel V1 (Current Channel)
The voltage outputs from the current transducers are connected
to the AD7751 here. Channel V1 has two voltage inputs, namely
V1A and V1B. These inputs are fully differential with respect to
V1N. However, at any one time only one is selected to perform
the power calculation—see Fault Detection section.
The analog inputs V1A, V1B, and V1N have the same maximum
signal level restrictions as V2P and V2N. However, Channel 1
has a programmable gain amplifier (PGA) with user-selectable
gains of 1, 2, 8, or 16—see Table I. These gains facilitate easy
transducer interfacing.
Figure 5 illustrates the maximum signal levels on V1A, V1B,
and V1N. The maximum differential voltage is
±
660 mV divided
by the gain selection. Again, the differential voltage signal on the
inputs must be referenced to a common mode, e.g., AGND. The
maximum common-mode signal is
±
100 mV as shown in Figure 5.
V1A, V1B
DIFFERENTIAL INPUT A
660mV/GAIN MAX PEAK
AGND
V
CM
V1A
V
CM
–
660mV
GAIN
COMMON-MODE
100mV MAX
V1N
+660mV
GAIN
V1
V1B
DIFFERENTIAL INPUT B
660mV/GAIN MAX PEAK
V1
Figure 5. Maximum Signal Levels, Channel 1
Table I.
Maximum
Differential Signal
±
660 mV
±
330 mV
±
82 mV
±
41 mV
G1
G0
Gain
0
0
1
1
0
1
0
1
1
2
8
16
Typical Connection Diagrams
Figure 6 shows a typical connection diagram for Channel V1.
Here the analog inputs are being used to monitor both the
phase and neutral currents. Because of the large potential
difference between the phase and neutral, two CTs (current
transformers) must be used to provide the isolation. Notice
both CTs are referenced to AGND (analog ground), hence
the common-mode voltage is 0 V. The CT turns ratio and
burden resistor (Rb) are selected to give a peak differential
voltage of
±
660 mV/Gain.
V1B
660mV
GAIN
CT
IN
V1A
AGND
Rb
R
f
CT
NEUTRAL
PHASE
IP
V1N
C
f
C
f
Rb
660mV
GAIN
R
f
Figure 6. Typical Connection for Channel 1
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