App. A Advantageous Use of Inverters (Notes on Electrical Noise)
A-10
No.
Tar ge t
device
Problem Noise prevention
Notes
5
Photo-
electric
relay
A photoelectric relay malfunctioned
when the inverter was operated.
Figure A-21
<Possible cause>
Although the inverter and
photoelectric relay are separated
by a sufficient distance but the
power supplies share a common
connection, it is considered that
conduction noise entered through
the power supply line into the
photoelectric relay.
1) Insert a 0.1µF capacitor
between the output common
terminal of the amplifier of the
photoelectric relay and the
frame.
Figure A-22
1) If a low-current
circuit at the
malfunctioning side
is observed, the
measures may be
simple and
economical.
6
Proximity
switch
(capaci-
tance
type)
A proximity switch malfunctioned.
Figure A-23
<Possible cause>
It is considered that the
capacitance type proximity switch
is susceptible to conduction and
radiation noise because of its low
noise immunity.
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.
Figure A-24
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superseded by a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).
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