YOKOGAWA WT500 User Manual page 79

3.10 Wiring the Circuit That You Will Measure with a Current Sensor
3-18
Note
• After wiring has been completed, the wiring system must be selected. See section 4.2,
"Selecting the Wiring System."
• The thick lines on the wiring diagrams are the sections where the current flows. Use wires
that are suitable for the current levels.
• To measure the apparent power and power factor more accurately on an unbalanced three-
phase circuit, we recommend that you use a three-voltage, three-current method with a
three-phase, three-wire system (3P3W; 3V3A).
• The current sensor input conversion feature can be used to convert the input signal data to
the corresponding data that would be acquired from direct measurements. For information
about how to set up this feature, see section 4.5, "Setting the Measurement Range for an
External Current Sensor (Optional)."
• Note that the frequency and phase characteristics of the current sensor affect the measured
data.
• Make sure that you have the polarities correct when you make connections. Otherwise,
the polarity of the measurement current will be reversed, and you will not be able to make
correct measurements. Be especially careful when connecting the clamp type current
sensor, because it is easy to reverse the connection.
• To minimize error when using a shunt resistor, follow the guidelines below when connecting
the external sensor cable.
• Connect the shielded wire of the external sensor cable to the L side of the shunt output
terminal (OUT).
• Minimize the area of the space between the wires connecting the shunt resistor to the
external sensor cable. This reduces the effects of the lines of magnetic force (which are
caused by the measurement current) and the external noise that enter the space.
Shunt resistor
I
±
• Connect a shunt resistor to the power earth ground as shown in the figure below. If you have
to connect the sensor to the non-earth side, use a wire that is thicker than AWG18 (conductive
cross-sectional area of approx. 1 mm
effects of common mode voltage. Take safety and error reduction into consideration when
constructing an external sensor cable.
Shunt resistor
• When the circuit under measurement is not grounded and the signal is high in frequency or
large in power, the effects of the inductance of the shunt resistor cable become large. In this
case, use an isolation sensor (CT, DC-CT, or clamp).
Clamp-type current sensor
Space between the
connection wires
External sensor cable
OUT H
(B9284LK, sold separately)
Shielded wire
OUT L
2
) between the sensor and the instrument to reduce the
Power meter
U
Voltage input terminal
±
External current sensor
input connector
Power meter
U
Voltage input terminal
±
External current sensor
input connector
WT500
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IM 760201-01E