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Electro-magnetic interference (EMI) and leakage currents
Noise
propagation path
When devices that handle low-level signals and are liable to malfunction due to electromagnetic noises, e.g.
instruments, receivers and sensors, are contained in the enclosure that contains the inverter or the converter unit,
or when their signal cables are run near the inverter, the devices may malfunction due to by air-propagated
electromagnetic noises. The following precautions must be taken:
• Install easily affected devices as far away as possible from the inverter or the converter unit.
• Run easily affected signal cables as far away as possible from the inverter or the converter unit, and its I/O
(a)(b)(c)
cables.
• Do not run the signal cables and power cables (inverter or converter unit I/O cables) in parallel with each other
and do not bundle them.
• Inserting a line noise filter into the output suppresses the radiated noise from the cables.
• Use shielded cables as signal cables and power cables and run them in individual metal conduits to produce
further effects.
When the signal cables are run in parallel with or bundled with the power cables, magnetic and static induction
noises may be propagated to the signal cables to cause malfunction of the devices and the following precautions
must be taken:
• Install easily affected devices as far away as possible from the inverter or the converter unit.
• Run easily affected signal cables as far away as possible from the inverter or the converter unit, and its I/O
(d)(e)(f)
cables.
• Do not run the signal cables and power cables (inverter or converter unit I/O cables) in parallel with each other
and do not bundle them.
• Use shielded cables as signal cables and power cables and run them in individual metal conduits to produce
further effects.
When the power supplies of the peripheral devices are connected to the power supply of the inverter or the
converter unit in the same line, its generated noises may flow back through the power supply cables to cause
(g)
malfunction of the devices and the following precautions must be taken:
• Install the line noise filter to the power cables (output cables) of the inverter.
When a closed loop circuit is formed by connecting the peripheral device wiring to the inverter or the converter unit,
leakage currents may flow through the earthing (grounding) cable of the inverter or the converter unit to cause the
(h)
device to malfunction. In that case, disconnecting the earthing (grounding) cable from the device may stop the
malfunction of the device.
Data line filter
Data line filter is effective as an EMI precautions. Provide a data line filter for the detector cable, etc.
EMI precautions example
Install filter on converter unit
input side.
Inverter
power supply
Separate inverter, converter
unit and power line by more
than 30cm (at least 10cm)
from sensor circuit.
Control power
supply
56
PRECAUTIONS FOR USE OF THE INVERTER
Enclosure
Line noise
Converter
filter
unit
Do not earth (ground) enclosure directly.
Do not earth (ground) control cable.
Countermeasure
Decrease carrier frequency
Line noise
Inverter
filter
Power
supply for
sensor
Do not earth (ground) shield but
connect it to signal common cable.
Install filter on inverter output side.
M
Motor
Use 4-core cable for motor
power cable and use one cable
as earth (ground) cable.
Use a twisted pair shielded cable
Sensor
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