Analog Devices UG-061, Руководство пользователя

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Evaluation Board User Guide UG-061
Rev. 0 | Page 9 of
USING A SHUNT RESISTOR AS THE CURRENT
TRANSDUCER
Figure 8 shows how a shunt resistor can be used to perform
the current-to-voltage conversion required for the ADE71xx/
ADE75xx/ADE51xx/ADE55xx. A shunt is a very cost effective
way to sense current in a 2-wire, single-phase application. Isola-
tion is not typically required in a 2-wire application and the
shunt has advantages over the CT arrangement. For example, a
shunt does not suffer from dc saturation problems and the
phase response of the shunt is linear over a very wide dynamic
range. Although the shunt is predominately resistive, it does
have parasitic reactive elements (inductance) that can become
significant, even at 50 Hz/60 Hz. This means that there can be a
small phase shift associated with the shunt. However, the phase
shift is easily compensated by writing to the phase calibration
register (PHCAL[7:0]) in the ADE71xx/ADE75xx/ADE51xx/
ADE55xx.
Figure 8 shows how the shunt can be connected to the evalua-
tion board. Two sense wires should be soldered to the shunt at
the copper/manganium junctions as shown. These sense wires
should be formed into a twisted pair to reduce the loop area,
which in turn reduces antenna effects. A connection for the
common-mode voltage can be made at the connection point for
the current-carrying conductor.
For an antitamper configuration, measuring both the phase and
neutral currents, two CTs can be used, as shown in Figure 6. Other
antitamper current sensor options include one shunt and one
CT, shown in Figure 7.
It is not possible to use two shunt resistors as current sensors for
use in an antitamper configuration with the ADE71xx/ADE51xx
products because, with a shunt resistor, the line or the neutral is
used as a ground reference for the ADE71xx/ADE51xx IC.
There is no isolation between the two current channels in the
ADE71xx/ADE51xx, and the line and neutral would be effec-
tively shorted together, which is dangerous.
PHASE
PGND
NEUTRAL
240V
LOA
D
JP13
R11
1k
Ω
R43
0
Ω
R42
0
Ω
R17
51
Ω
JP16
JP14
R3
1k
Ω
JP1
C26
0.033µF
C23
0.033µF
R41
0
Ω
R16
51
Ω
JP11
R4
1k
Ω
JP19
C24
0.033µF
ADE7169/
ADE5169
IP
IPA
IN
IPB/FP26
IN
IPB
IPA
IN
IPB
P11 1
P11 2
P11 3
08600-
008
P3-2 VN
Figure 7. Connecting One Shunt and One CT to the Current Channels
JP13
R11
1k
Ω
R43
0
Ω
R42
0
Ω
R17
51
Ω
JP16
JP14
R3
1k
Ω
JP1
C26
0.033µF
C23
0.033µF
R41
0
Ω
R16
51
Ω
JP11
P3-2 VN
R4
1k
Ω
JP19
C24
0.033µF
ADE7169/
ADE5169
IP
IPA
IN
IPB/FP26
IN
IPB
IPA
IN
IPB
P11 1
P11 2
P11 3
08600-
060
PHASE
350 µ
Ω
220V
LOA
D
NEUTRAL
Figure 8. Shunt Resistor Used as Current Transducer