352
Photoelectric Sensors
2
Photoelectric Sensors,
Standard Sensors,
thru-beam sensors
2
.1.4
Photoelectric Sensors,
Standard Sensors,
thru-beam sensors
2
.1.4
Photoelectric Sensors,
Standard Sensors,
retroreflective sensors
2
.1.3
Photoelectric Sensors,
Standard Sensors,
retroreflective sensors
2
.1.3
Photoelectric Sensors,
Standard Sensors,
diffuse mode sensors
2
.1.2
Photoelectric Sensors,
Standard Sensors,
diffuse mode sensors
2
.1.2
Photoelectric Sensors,
Standard Sensors,
diffuse mode sensors with background suppression
2
.1.1
Photoelectric Sensors,
Standard Sensors,
diffuse mode sensors with background suppression
2
.1.1
Photoelectric Sensors,
Standard Sensors,
distance sensors
2
.1.5
Photoelectric Sensors,
Standard Sensors,
fiber optic sensors
2
.1.6
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5.
Fiber Optic Systems
The optical characteristics of a photoelectric sen-
sor with a fiber optic cable are similar to those of a
thru-beam sensor or a diffuse mode sensor, de-
pending on the housing design.
Thru-beam systems have one fiber optic cable
each for the emitter and receiver, while in diffuse
systems the light is passed through separate emitting and receiv-
ing fibers in a single fiber optic cable.
The emitter and receiver are arranged in one housing. The opti-
cally active area runs from the device to the sensing point using
flexible fiber optic cables made of glass or plastic fibers. Due to
their small optically active areas, fiber optic systems are suit-
able for detecting small details at close range. Special fiber optic
cables are used with a coaxial or mixed fiber arrangement and
small fiber diameters (plastic fibers: a few hundred µm, glass fi-
bers: typically 50 µm).
The large opening angle at the light exit of the fiber optic cable
(
approx. 70°) also enables it to be used to achieve shorter detec-
tion ranges than standard photoelectric sensors or
light sensors; if necessary, these can be increased using suitable
lens attachments.
Glass or plastic?
When choosing a suitable fiber optic cable, users can choose
between plastic or glass fiber optic. The characteristics of both
these materials are briefly outlined below.
•
Plastic fiber optics
consist of a single PVC-sheathed fiber. As the fiber optic
cable material is lightweight and very flexible, it can be used
on machines with moving parts. One advantage in particular
is the individual assembly of the fibers. The standard length is
2
m. The cutter provided can be used to shorten the fiber optic
cable easily to the length required for the application. Two
different fiber diameters and a range of different fiber heads
are available to choose from.You are sure to find a type to suit
your application.
•
Glass fiber optics
consist of many individual fibers, each with a diameter of
approx. 50 µm. Depending upon the application, sheathing
is available in stainless steel, PVC, metal and silicone, or
silicone. Due to the low optical attenuation of glass fibers
compared to plastic fibers, larger sensing ranges are possible.
The robust mechanical design of the stainless steel sheathing
means that the cables can be used at temperatures of up to
300
°C.You will find a suitable solution for your application
from the range of fiber heads, each of which can be combined
with the sheathing materials.
To help you choose the right product, the "Fiber Optic Devices"
section highlights which fiber optic cables are suitable for the in-
dividual sensor types.
6.
Light Grids for Clear Object Detection
The devices in the PR and LG series are high-res-
olution light curtains for detecting very small posi-
tion-independent objects.
The use of special low-noise receiver levels and
a sophisticated evaluation algorithm enables even
highly transparent objects with a high excess gain to be detected
reliably.
Crossed beam evaluation:
Each emitter emits light to each receiver. This results in a very
high sensor resolution.
Automatic calibration:
After turning on the supply voltage (model number –W) or ex-
ternally activating the calibration input (model number –F), the
sensor automatically calibrates itself. Each individual emitter-
receiver distance is calibrated separately.
Example PR16:
16
emitters and 16 receivers for crossed beam evaluation result
in 256 light beams being individually evaluated internally. Fur-
thermore, the signal threshold for the individual emitter-receiver
distances is permanently adjusted within a certain bandwidth
during operation. This means that the sensor compares the
stored value with the current measured reception level at certain
time intervals.
If these two values differ over time (due to dust on the lens or
slight misalignment) the receiver threshold for each of the individ-
ual light paths is redefined. This ensures that highly transparent
objects are detected even in harsh industrial conditions.
RLG28 retroreflective area sensor
A very effective operating principle
The retroreflective area sensor uniquely
combines the advantages of a retrore-
flective sensor with those of a light grid.
A retroreflective area sensor contains sev-
eral emitters and receivers in one housing
and, with a reflector positioned opposite
it, forms a detection field with a consistent
width and height across the relevant detec-
tion range. When the light beams within the
detection area are interrupted by an object,
the switching function is triggered.
The use of standard photoelectric sensors
is often problematic when detecting objects
with an appearance that differs occasionally. More
specifically, objects with varying front edges regularly overload
devices with single-point detection characteristics.
Photoelectric Sensors
