4-3
H
Types of Noise and Typical Noise Sources
Kind
Generation
Machine or component
Signal waveform
Coil surge
A coil generates a surge
when the voltage
imposed on the coil is
turned on and off.
Relay
Solenoid
Contactor
Time
V
ol
ta
ge
Capacitor charge current A high-charge current
flows when voltage is
imposed on a capacitor.
Built-in power supply
Power supply
Capacitive-discharge
machine
C
ur
re
nt
Time
Pulse voltage
Pulse voltage from PWM
(see note).
Servo Driver
Inverter
Switching current
Time
V
ol
ta
ge
Arc discharge
Radical voltage changes
with discharge.
Welding machine
Arc-discharge tube
Time
V
ol
ta
ge
Note
PWM is an abbreviation for pulse-width modulation, which makes average voltage changes by
intermittently turning the voltage on and off with short intervals.
4-1-3 Noise Transmission Paths
Noise is transmitted through the following four paths.
D
Capacitive Coupling Path
Noise signals with radical changes are transmitted from one line to another through an electric field gen-
erated between the signal lines like an imaginary capacitor. The efficiency of such noise transmission
will increases in accordance with an increase in noise-signal change level and a decrease in transmis-
sion path distance.
Effects
Noise transmission between signal cables.
Motor leakage current.
Sensor malfunctions.
Radical signal changes
Signals are transmitted through the
electric field like an imaginary capacitor.
Countermeasures Against Noise
Chapter 4
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