Using A Ct As The Current Transducer - Analog Devices UG-061 User Manual

UG-061

USING A CT AS THE CURRENT TRANSDUCER

Figure 5 shows how a current transformer (CT) can be used as a
current transducer in a single-phase, 2-wire distribution system.
The CT secondary current is converted to a voltage by using a
burden resistance across the secondary winding outputs. Care
should be taken when using a CT as the current transducer. If
the secondary is left open, that is, no burden is connected, a
large voltage may be present at the secondary outputs. This can
cause an electrical shock hazard and potentially damage
electronic components.
When using a CT as the current sensor, the antialias filters
should be enabled by opening Jumper JP19 and Jumper JP1
(see Figure 8).
Most CTs have an associated phase shift of between 0.1° and 1°
at 50 Hz/60 Hz. This phase shift or phase error can lead to signifi-
cant energy measurement errors, especially at low power factors.
PHASE
240V
NEUTRAL
PHASE
240V
NEUTRAL
P11 1
IPA
JP11
P11 2
IN
JP14
IPB
P11 3
JP13
Figure 5. CT Sensor Connection to Current Channel
P11 1 IPA
JP11
P11 2 IN
JP14
P11 3 IPB
JP13
Figure 6. Connecting Two CTs to the Current Channels
Rev. 0 | Page 8 of
Evaluation Board User Guide
However, this phase error can be corrected by writing to the
phase calibration register (PHCAL[7:0]) in the ADE7169/
ADE5169. The software supplied with the ADE7169/ADE5169
evaluation board allows user adjustment of the phase calibra-
tion register. See the Evaluation Board Software section for
more information.
The maximum analog input range and gain for the current and
voltage channels are set via the gain register (see the respective
data sheet). The evaluation software allows the user to configure
the channel range and gain. This means that the maximum
peak differential signal on Channel 1 is 0.5 V (at gain = 1).
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, as shown in Figure 7.
JP19
R41
R4
0Ω
1kΩ C24
0.033µF
R16
51Ω
JP1
R42
R3
C23 0Ω
1kΩ
0.033µF
R17
51Ω
JP16
R11 R43
C26
1kΩ 0Ω
0.033µF
JP19
R41
R4
1kΩ C24
0.033µF
R16
51Ω
JP1
R42
R3
C23
1kΩ
0.033µF
R17
51Ω
JP16
R11 R43
1kΩ C26
0.033µF
IPA
IP
ADE7169/
ADE5169
IN
IN
IPB/FP26
IPB
IPA
IP
0Ω
ADE7169/
ADE5169
IN
IN
0Ω
IPB/FP26
IPB
0Ω