Cut Sheet

Volume 8—Sensing Solutions CA08100010E—November 2012 www.eaton.com V8-T12-25
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12.1
Sensor Learning Course
Learning Module 23: Limit Switches, Proximity Sensors and Photoelectric Sensors
Basic Operation of Photoelectric Sensors
The operation of the
photoelectric sensor is quite
simple. A source LED sends
a beam of light, which is
picked up by a
photodetector.
When an object moves into
the path of the light beam,
the object is detected.
Let’s look at how a
photoelectric sensor works.
Photoelectric Sensor Operation
Notes
1
Power Supply: Provides regulated DC
voltage and current to the sensor
circuitry.
2
Modulator: Generates pulses to cycle
amplifier and LED at desired frequency.
3
Source Current Amplifier
4
Source LED
5
Output: Performs switching routine
when directed to do so by the
demodulator.
6
Demodulator: Sorts out the light
thrown out by the sensor from all other
light in the area. If the demodulator
decides the signals it receives are okay,
it signals the output.
7
Detector Amplifier: Blocks current
generated by the background light. It
also provides amplification of the
detected signal to a usable level, and
sends it through to the demodulator.
8
Photodetector: Either a photodiode or a
phototransistor device, selected for a
maximum sensitivity at the source LEDs
emitted light wave-length. Both the
source LED and the detector have
protective lenses. When the detector
picks up the light, it sends a small
amount of current to the detector
amplifier.
The Light Source
The light generated today
by a photoelectric sensor
comes from light emitting
diodes, called LED. Using
LEDs offers many significant
advantages:
●
Can be rapidly switched
and instantly turned ON
and OFF
●
Extremely small
●
Consume very little power
●
Generate a negligible
amount of heat
●
Life exceeds 100,000
hours (11 years)
continuous use
●
Easily modulated to block
false sensor triggering
from ambient light
Target or
Reector
a
b
c
d
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f
g
h
Lens
Lens