Some noises enter the inverter causing it to incorrectly operate, and others are radiated by the inverter causing misoperation of peripheral devices. Though the inverter is designed to be insusceptible to noise, it handles low-level signals, so it requires the following basic measures to be taken. Also, since the inverter chops the output at high carrier frequencies, it could generate noise. If these noises cause peripheral devices to misoperate, measures should be taken to suppress noise. The measures differ slightly depending on noise propagation paths.
1) Basic measures
y Do not run the power cables (I/O cables) and signal cables of the inverter in parallel with each other and do not bundle them.
y Use twisted shield cables for the detector connecting and control signal cables and connect the sheathes of the shield cables to terminal SD.
y Ground the inverter, motor, etc. at one point.
2) Measures against noise which enters and causes misoperation of the inverter
When devices which generate noise (devices which use magnetic contactors, magnetic brakes, many relays, for example) are installed near the inverter, the inverter may misoperate due to noise. The following measures must be taken:
y Provide surge suppressors for devices that generate noise to suppress noise.
y Fit data line filters (refer to page 39) to signal cables.
3) Measures against noises which are radiated by the inverter causing misoperation of peripheral devices.
Inverter-generated noises are largely classified into those radiated by the cables connected to the inverter and inverter main circuit (I/O), those electromagnetically and electrostatically inducted to the signal cables of the peripheral devices close to the main circuit power supply, and those transmitted through the power supply cables.
Inverter-generated noise
Air-propagated noise
xxxPath 3)
xxxPath 2)
xxxPath 1)
xxxPath 4), 5)
xxxPath 6)
xxxPath 8)
xxxPath 7) Magnetic induc-
tion noise Static induction noise
Cable Propaga- ted noise
Noise directly radiated by inverter
Noise radiated by power cables
Noise radiated by motor cables
Noise propagated through power cables
Leakage noise from ground cable due to leakage current
Instrument Receiver
Inve- rter
IM
Sensor power supply
Motor
Telephone
Sensor
7) 2)
1) 3)
4) 5)
7) 2) 6)
3)
8)
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Noise Path Measures
1), 2), 3)
When devices which handle low-level signals and are susceptible to misoperation due to noise (such as instruments, receivers and sensors) are installed near the inverter and their signal cables are contained in the same panel as the inverter or are run near the inverter, the devices may be misoperated by air-propagated noise and the following measures must be taken:
(1) Install easily affected devices as far away as possible from the inverter.
(2) Run easily affected signal cables as far away as possible from the inverter.
(3) Do not run the signal cables and power cables (inverter I/O cables) in parallel with each other and do not bundle them.
(4) Insert line noise filters onto I/O and radio noise filters into inputs to suppress cable-radiated noises.
(5) Use shielded cables for signal cables and power cables and run them in individual metal conduits to further reduce effects.
4), 5), 6)
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 causing misoperation of the devices and the following measures must be taken:
(1) Install easily affected devices as far away as possible from the inverter.
(2) Run easily affected signal cables as far away as possible from the inverter.
(3) Do not run the signal cables and power cables (inverter I/O cables) in parallel with each other and do not bundle them.
(4) Use shielded cables for signal cables and power cables and run them in individual metal conduits to further reduce effects.
7)
When the power supplies of the peripheral devices are connected to the power supply of the inverter within the same line, inverter-generated noise may flow back through the power supply cables causing misoperation of the devices and the following measures must be taken:
(1) Install the radio noise filter (FR-BIF) to the power cables (input cables) of the inverter.
(2) Install the line noise filter (FR-BLF, FR-BSF01) to the power cables (I/O cables) of the inverter.
8)
When a closed loop circuit is formed by connecting the peripheral device wiring to the inverter, leakage current may flow through the ground cable of the inverter causing misoperation of the device. In such a case, disconnection of the ground cable of the device may cause the device to operate properly.
z Data line filter
Noise entry can be prevented by providing a data line filter for the detector or other cable.
z Data examples
By decreasing the carrier frequency, the noise terminal voltage* can be reduced.
Use Pr. 72 to set the carrier frequency to a low value (1kHz).
Though motor noise increases at a low carrier frequency, selection of Soft-PWM will make it unoffending.
By using shielded cables as signal cables, induction noise can be reduced greatly (1/10 to 1/100). Induction noise can also be reduced by moving the signal cables away from the inverter output cables.
(Separation of 30cm (11.81 inches) reduces noise to 1/2 to 1/3.)
By fitting the FR-BSF01 or BLF on the inverter output side, induction noise to the signal cables can be reduced.
Differences between noise terminal voltages at different carrier frequencies
0 20 40 60 80 100 120
0.1 1 10
Noise frequency (MHz)
Noise terminal voltage (dB)
Conditions
Average terminal voltage 0dB=1àV
120dB=1V
Carrier frequency 10kHz
Carrier frequency 1kHz
Noise induced to signal cables by inverter output cables
5cm
Line-to-line distance d (cm) 20
40 60 80 100
0 10 20 30 40 50
Induction voltage (dB)
d(cm) Motor
Measuring instrument Terminal Inverter
FR-BLF FR-BSF01
(4T) Conditions
Inverter: FR-E520-3.7K-NA Motor: FR-JR 4P 3.7kW (5HP) Output frequency: 30Hz Noise form: Normal mode Parallel cable
Twisted pair cable Coaxial cable
* Noise terminal voltage: Represents the magnitude of noise propagated from the inverter to the power supply.
z Example of measures against noise
Inverter
FR- BIF
Sensor
Use 4-core cable for motor power cable and use one wire as earth cable.
Power supply for sensor
Use twisted pair shielded cable.
Inverter power supply
Control power supply
Do not ground shield but connect it to signal common cable.
Do not ground control box directly.
Do not ground control cable.
Separate inverter and power line 30cm (11.81inches) or more (at least 10cm (3.94inches)) from sensor circuit.
Install filter FR-BIF to inverter input side.
Control box Reduce carrier frequency.
Motor
FR- IM
BSF01
FR- BSF01
FR-BLF FR-BSF01 Install filter to inverter input side.
FR-BLF FR-BSF01 Install filter to inverter output side.
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