Automation Canada - Automation in 2021 - 32

PHOTOELECTRIC SENSORS
Photoelectric sensors detect and measure physical objects or
quantities by emitting a field or beam of electromagnetic radiation. The
sensors allow detection by measuring changes and differences in the
return signal.
" Photoelectric sensors are commonly used in all types of
automation. " says Freeman. " Anytime you see a conveyor, there's
probably a myriad of photoelectric sensors on that conveyor to sensor
position or count objects. But photoelectric sensors are also used for
several different applications. Different sensing modes can be used for
level, for presence, and even for position. The most common sensing
modes are emitter-receiver, retro-reflective and diffused (proximity
mode). Each mode has advantages and disadvantages depending on
the sensing application. In addition to digital outputs on the sensors,
analog outputs are also available in some modes. A photoelectric
sensor with an analog output can determine the exact position of an
object over a given distance as the object moves. "
FIBER OPTIC SENSORS
Fiber optic sensors are photoelectric and utilize optical fiber
connected to a light source to allow for detection in tight spaces or
where a small profile is beneficial. The optical fiber is transparent and
made from a silica or glass material, and sometimes plastic. The fibers
are very thin oſten with a diameter just thicker than human hair. The fiber
transmits light between the two ends to produce an electrical signal.
" There are two main areas I see fiber optic sensors being used, "
explains Freeman. " One is when you physically can't mount a
photoelectric or a proximity sensor to detect in a small area. Or it may
be used on small conveyors where you have small items to detect.
Imagine you're going to count the needles for vaccines.
You'd need a very small beam for that needle to break, so that you can
count it. Generally, those are high-speed applications. Just imagine,
needles going by on a conveyor and how fast the sensor response
would need to be. The amplifier is just as important as the fiber itself.
The amplifier processes the signal from the fiber and can produce
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microsecond outputs, output based on color contrast or provide pulse
stretching capabilities depending on the model. "
There are numerous categories of sensors. This is a broad overview of
four commonly used sensors that many industrial applications use and
will select for their applications. Over time, not only will automation
advance, but so will the capabilities and characteristics of the sensors.
A best practice for sensor selection is to align with a distributor and
vendor who has broad insight into many different applications. Work
with vendors to select the proper sensor given each unique
circumstance and the technology that is available. Being aware of the
basic types of sensors and smartly working with vendors will put anyone
in good stead when the time comes to install or replace sensors in the
ever-progressing automation environment in which the world now
operates.
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