349
Photoelectric Sensors
2
Germany: +49 621 776-4411
Consider the General Notes on the Information in the Pepperl+Fuchs Product Catalogs
Pepperl+Fuchs Group
fa-info@de.pepperl-fuchs.com
USA: +1 330 486 0001
fa-info@us.pepperl-fuchs.com
Singapore: +65 6779 9091
fa-info@sg.pepperl-fuchs.com
Copyright Pepperl+Fuchs
2.
Diffuse Mode Sensors
In principle, a diffuse mode sensor is constructed
similarly to a retroreflective sensor. However, it
does not use a reflector and the receiver evaluates
the light reflected from the detected object instead.
R
E
O
Due to the diffuse reflection (remission) by the object, the sen-
sor’s detection range is reduced compared with that of the retro-
reflective sensor. This detection range is the maximum distance
from the emitter at which an object can be reliably detected.
Sensitivity adjuster
Special versions of diffuse mode sensors
The standard feature of the diffuse mode sensor–
that it reacts sensitively to the surface finish of the
target–is utilized in contrast sensors and color
sensors.
Contrast sensors
This sensor evaluates the difference in brightness between the
target and a marking that is applied to it. The color of the emitter
light or the color of the print mark is selected to allow as much
contrast as possible. Our contrast sensors are fitted with a three-
color LED as the light source. The best possible transmitter light
color is selected automatically by the sensor during the Teach-in
process. A large number of sensors are arranged in accordance
with the auto-collimation principle, i.e., the transmitter and receiv-
er and located on a common optical axis (monocular system).
This enables the lens to be moved and makes the installation
position of the sensor very flexible.
Luminescence sensors
The luminescence sensor–a version of the contrast sensor–
works with modulated ultraviolet light. Suitable materials (lumino-
phores) that are applied to the target become photoluminescent
when exposed to the light.These materials include optical bright-
eners in white paper, certain chalks, varnishes, oils, fats, and in
highlighters.
The light emitted from the luminophores to the receiver has a lon-
ger wavelength than that emitted from the transmitter; it is within
the visible spectral range. Due to modulation and the precisely
defined frequency shift between the transmitter light and the re-
ceiver light, luminescence sensors are barely affected by inter-
fering light sources and therefore function reliably.
Color sensors
While a standard contrast sensor evaluates only the differences
in brightness in a specific spectral range that is predetermined
by the light color of the emitter, the color sensor divides the light
reflected by the object into several subspectra and provides an
intensity value for each of these subspectra. The distribution of
these values reflects the spectral characteristics and the color
of the target.
Visolux color sensors operate according to the three-range pro-
cess, which can be either active or passive.
•
Active three-range process:
The target is illuminated sequentially with the three emitter
colors (red, green, and blue). The amount of reflected light is
measured individually for each color. The color of the target is
clearly determined based upon the three values obtained this
way.
•
Passive three-range process:
The target is illuminated with white emitter light. The light
source is, for example, a white LED. The red, green, and blue
portions of the reflected light are then filtered out and the
amount of light is determined in each case. Three receivers
are used for this and the values obtained are used to
determine the color of the target.
Introduction
