Automation Canada - Automation in 2021 - 31

A CONCISE OVERVIEW OF COMMON SENSORS USED IN AUTOMATION
In today's increasingly wired world, sensors take center stage. There
are many options when it comes to sensors. Here's an overview of some
leading categories of industrial sensors used in automation in
consultation with Russ Freeman, a product portfolio manager, with
Allied Electronics and Automation in Ft. Worth, Texas.
properly. So, for the dirty, cruddy places where you're wanting to sense
metal, inductive sensors are perfect. Also, it's easy to confirm or
eliminate an inductive proximity sensor as a solution by two questions.
First, is the target metal? Second, can I mount the sensor really close? If
the answer to both questions is yes, then an inductive proximity sensor
may be the answer. If you get a no to either question, you will probably
not be able to use an inductive proximity sensor. "
CAPACITIVE PROXIMITY SENSORS
Capacative proximity sensors feature parallel plates, much like a
capacitor. When an object produces changes in capacitance, the
sensor is activated. These sensors, by design, are generally used with
non-ferrous materials and ideal for close-range applications, such as
detection or level monitoring. They can be greatly affected by their
INDUCTIVE PROXIMITY SENSORS
Inductive proximity sensors provide non-contact detection of metallic
objects. Some within this category can target both ferrous and
non-ferrous metals, while others sense only one or the other. Inductive
proximity sensors are suited for many industrial applications, and some
are rated for use in hazardous environments. Due consideration must be
given to their use in the presence of other inductive proximity sensors,
and the environment in which they operate.
" An inductive proximity sensor is my first choice because it is
extremely rugged, " explains Freeman. " Basically, you can put as much
dirt and grease or other non-metal contaminates on the face of that
sensor, and it will still work as long as you don't exceed the rated
sensing distance of the sensor.
Whereas with a photoelectric sensor, dirt and grease on the lens will
decrease the sensing distance and causing the sensor to not work
environment and interaction with other sensors.
" A capacitive proximity sensor detects based off dielectric content of
an item, which is basically water content, " explains Freeman. " This
allows you to tune out a lower dielectric and detect a higher dielectric.
For example, capacitive proximity sensors can be used on a tank sight
glass to determine liquid level in the tank.
You must be careful to determine exactly what liquid you are sensing,
because if you're sensing something such as gasoline, the dielectric of
gasoline is very close to the same dielectric of glass, and properly
tuning the sensor may be difficult. Whereas if the liquid in the sight glass
is water, it would be much easier to tune because of the large dielectric
difference of glass and water. One common application is sensing liquid
level through a plastic reservoir. This eliminates the need to put a hole in
the tank to mount the sensor. However, make sure the tank thickness
does not exceed the sensing range of your sensor. Another item to note
with a capacitive sensor is that changes in heat and/or humidity will
affect the tuning of the sensor. "
CANADIAN AUTOMATION
VOLUME 3, ISSUE 4
32
https://www.alliedelec.com/expert/a-concise-guide-to-wire-and-cable-selection/ https://ca-en.alliedelec.com/
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