Cut Sheet

Volume 8—Sensing Solutions CA08100010E—November 2012 www.eaton.com V8-T12-23
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12.1
Sensor Learning Course
Learning Module 23: Limit Switches, Proximity Sensors and Photoelectric Sensors
Environment
Many of the same factors
that affect inductive proximity
sensors, also affect
capacitive sensors,
only more so.
●
Embeddable mounting—
capacitive sensors are
generally treated as non-
shielded devices, and
therefore, are not
embeddable
●
Flying chips—they are
more sensitive to both
metallic and nonmetallic
chips and residue
●
Adjacent sensors—more
space between devices is
required due to the
greater, non-shielded
sensing range
●
Target background—
because of both the
greater sensing range, and
its ability to sense metallic
and nonmetallic materials,
greater care in applying
these sensors is needed
when background
conditions are present
●
Ambient atmosphere—the
amount of humidity in
the air may cause a
capacitive sensor to
operate even when no
target is present
●
Welding magnetic fields—
capacitive sensors are
generally not applied in a
welding environment
●
Radio Frequency
Interference (RFI)—in the
same way that inductive
proximity sensors are
affected, RFI interferes
with capacitive sensor
circuitry
●
Showering arc (EFT)—
induced electrical noise
affects these sensors in
the same way it does for
an inductive sensor
In the Workplace
On the fill line at Bud Springs Natural Water, two liter plastic
bottles pass along beneath a fill nozzle.
A Capacitive Proximity Sensor “Sees Through” a Wall to Find the Target
As water fills each bottle, a capacitive proximity sensor detects
when the water reaches the specified level. As the sensor is
more sensitive to water than it is to plastic, the sensor can “see
through” the bottle wall.
Review 5
Answer the following questions without referring to the material
just presented. Begin the next section when you are confident
that you understand what you’ve already read.
1. The operation of a capacitive proximity sensor is based on
dielectric capacitance. TRUE FALSE
2. The four main parts of a capacitive proximity sensor are:
________________________
________________________
________________________
________________________
3. By measuring the change in capacitance as an object enters
the field generated by the oscillator, it can be used for an on/
off switching function. TRUE FALSE
4. When feedback capacitance is detected, the oscillation
ends. TRUE FALSE
5. When sensing metal targets, a derating factor must be
applied. TRUE FALSE
6. The transparency of the container has no effect on the
sensing. TRUE FALSE
Answers to Review 5 are on Page V8-T12-41.