Appendix A Trouble-free Use of Inverters (Notes on electrical noise)
Appendix-10
Table A-2 Examples of Noise Prevention Measures (Continued)
No.
Target
device
Phenomena Measure
Notes
5 Photo-
electric
relay
A photoelectric relay
malfunctioned when the inverter
was operated.
<Possible cause>
While the inverter is sufficently
away from the photoelectric
relay, the power source is
connected in common.
Conducted noise has entetrd
from the power source line.
1) Insert a 0.1 μF capacitor
between the output
common terminal of the
amplifier of the photoelectric
relay and the frame.
1) If a low-current
circuit at the
malfunctioning
side is observed,
the measures may
be simple and
economical.
6 Proximity
switch
(capacitance
type)
A proximity switch
malfunctioned.
<Possible cause>
The electrostatic capacitive
proximity switch has a low noise
immunity, and is vulnerable to
circuit conducted noise and
radiated noise.
1) Install an LC filter at the
output side of the inverter.
2) Install a capacitive filter at
the input side of the inverter.
3) Ground the 0 V (common)
line of the DC power supply
of the proximity switch
through a capacitor to the
box body of the machine.
1) Noise generated in
the inverter can be
reduced.
2) The switch is
superseded by a
proximity switch of
superior noise
immunity (such as
a magnetic type).
7 Pressure
sensor
A pressure sensor
malfunctioned.
<Possible cause>
Noise enters from the box body
via the shielded wire to cause
malfunctioning of the pressure
sensor.
1) Install an LC filter on the
input side of the inverter.
2) Connect the shield of the
shielded wire of the
pressure sensor to the 0 V
line (common) of the
pressure sensor, changing
the original connection.
1) The shielded parts
of shield wires for
sensor signals are
connected to a
common point in
the system.
2) Conducted noise
from the inverter
can be reduced.
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