Mitsubishi Electronics A800 ユーザーズマニュアル

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Electro-magnetic interference (EMI) and leakage currents
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3
3.1.2
Countermeasures against inverter-generated 
EMI
Some electromagnetic noises enter the inverter or the converter unit to cause its malfunction, and others are radiated by the 
inverter or the converter unit to cause the peripheral devices to malfunction. Though the inverter or the converter unit is 
designed to have high immunity performance, it handles low-level signals, so it requires the following basic techniques. Also, 
since the inverter chops outputs at high carrier frequency, that could generate electromagnetic noises. If these 
electromagnetic noises cause peripheral devices to malfunction, EMI countermeasures should be taken to suppress noises. 
These techniques differ slightly depending on EMI paths.
 • Basic techniques
- Do not run the power cables (I/O cables) and signal cables of the inverter or the converter unit in parallel with each other 
and do not bundle them.
- Use shielded twisted pair cables for the detector connecting and control signal cables and connect the sheathes of the 
shielded cables to terminal SD.
- Ground (Earth) the inverter or the converter unit, motor, etc. at one point.
 • Techniques to reduce electromagnetic noises that enter and cause a malfunction of the inverter or the converter unit (EMI 
countermeasures)
When devices that generate many electromagnetic noises (which use magnetic contactors, electromagnetic brakes, many 
relays, for example) are installed near the inverter or the converter unit and it may malfunction due to electromagnetic 
noises, the following countermeasures must be taken: 
- Provide surge suppressors for devices that generate many electromagnetic noises to suppress electromagnetic noises.
- Install data line filters (
) to signal cables.
- Ground (Earth) the shields of the detector connection and control signal cables with cable clamp metal.
 • Techniques to reduce electromagnetic noises that are radiated by the inverter to or converter unit cause the peripheral 
devices to malfunction (EMI countermeasures)
Noises generated from the inverter or the converter unit are largely classified into those radiated by the cables connected to 
the inverter or the converter unit and its main circuits (I/O), those electromagnetically and electrostatically induced to the 
signal cables of the peripheral devices close to the main circuit power supply, and those transmitted through the power 
supply cables. 
Noise directly radiated 
from the inverter or the 
converter unit
Inverter generated
electromagnetic 
noise
Air propagated 
noise
Electrical path 
propagated noise
Electromagnetic 
induction noise
Electrostatic 
induction noise
Path (c)
Path (b)
Path (a)
Path (h)
Path (g)
Path (d), (e)
Path (f)
Noise propagated through 
power supply cable
Noise radiated from 
power supply cable
Noise radiated from 
motor connection cable
Noise from earthing 
(grounding) cable due to 
leakage current
M
(a)
(b)
(c)
(c)
(h)
(g)
(e)
(g)
(d)
(f)
Converter
unit
Inverter
(a)
Motor
Telephone
Sensor
Instrument
Receiver
Sensor
power supply