5-16
Change earth: Do not use a common earth for instrumentation and the inverter. Noise may
propagate from the earth wire. Additionally, use thick earth wires.
Isolated power
supply:
Noise may propagate from the power supply of instrumentation.
To isolate the wiring from the power supply of the inverter, it is recommended
to change the power wiring, or use an isolated transformer (TRAFY) for the
power supply or a noise-suppressing transformer.
Filtering:
To cut ringing and high-frequency noise, create a (low pass filter) LPF by
connecting a condenser in parallel at the signal input/output terminal.
Add inductance
components:
Insert inductance components such as choke coils in series in the signal
circuit, or pass the cable through a ferrite core ring. This will help to keep the
impedance of the signal lines high to counteract high frequency noise.
When filtering and adding inductance components, with fast communication speeds the signal waveform may
become irregular, causing transmission errors. If this happens, use function code H34 to slow down the
communication speed.
Normal si
nal
Irre
ular waveform
Effect of filtering
This method separates ringing due to signal reverberation and normal mode noise from the normal
signal. Generally, the former is a higher frequency than the signal and so can be separated with a
LPF.
Normal mode noise
Ringing
Signal
Condenser
Terminating resistor (100 Ω)
about 0.01-0.001
F
Inverter or master device or converter
Receive terminal
Adding inductance components
Ferrite
core
Inverter
Maste
Pass throu
h
or wind 2-3 times
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