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FAQ00341 of Photoelectric Sensors FAQ

FAQ No. FAQ00341

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Our Photoelectric Sensors malfunction when the power supply of an inverter motor or other equipment is switched ON or OFF. What's causing this, and what can we do to resolve it?


It's possible that the malfunction is due to electrical noise. Try a countermeasure for noise. Different countermeasures should be used depending on factors such as the path of noise entry, the frequency component, and the peak value.
Typical countermeasures for various types of noise are shown in the following table.

Type of noiseNoise intrusion path and countermeasure
Before countermeasureAfter countermeasure
Common mode noise
(inverter noise)
(Common noise
applied between the
mounting board and
the +V and 0-V
lines, respectively.)
Noise enters from the noise source
through the frame (metal).
(1) Ground the inverter motor (to 100 Ω or less)
(2) Ground the noise source and the power supply
(0-V side) through a capacitor (film capacitor, 0.22
µF, 630 V).
(3) Insert an insulator (plastic, rubber, etc.)
between the Sensor and the mounting plate (metal).
Radiant noise
(Ingress of high-
waves directly into
Sensor, from
power line, etc.)
Noise propagates through the air
from the noise source and directly
enters the Sensor.
Insert a shield (copper) plate between the Sensor
and the noise source e.g., a switching power supply).
Separate the noise source and the Sensor to a
distance where noise does not affect operation.
Power line noise
(Ingress of electromag-
netic induction from
high-voltage wires
and switching noise
from the switching
power supply)
Noise enters from the power line.
Insert a capacitor (e.g., a film capacitor), noise
filter (e.g., ferrite core or insulated transformer),
or varistor in the power line.