The document provides an overview of various types of proximity sensors, which detect objects without contact using different methods such as sound, electromagnetic waves, and optical techniques. It details the principles and components of inductive, capacitive, ultrasonic, magnetic, and optical sensors, highlighting their applications and operation mechanisms. Each sensor type has unique functionalities suited for different industrial uses and environmental conditions.

1. PROXIMITY
SENSOR Prepared by
Ujjwal Kumar Choubey
ujjwalchoubey80@gmail.com

2. The proximity sensor is a group of sensors that can identify the object without getting
in contact with it, in various ways (Sound, magnetic, electromagnetic waves, optical).
It is widely used in all the industries and appliances used in daily basic.

3. TYPES OF PROXIMITY SENSOR
Proximity
Sensor
Inductive Capacitive Ultrasonic Magnetic
Variable
Reluctance
Reed
Switch
Optical
Through-
Beam
Reflective
Retro
Reflective
Polarized
Reflection with
Reflector
Diffuse-
Reflective

4. INDUCTIVE PROXIMITY SENSOR
An inductive sensor is a device that works on
the principle of electromagnetic induction to
detect an objects.
It consists of following parts: sensing face,
oscillator, trigger level signal converter, output
amplifier.
The oscillator generates an electromagnetic
field that radiates out from the sensing face,
when the metallic object comes in the range of
electromagnetic field the current is induced
through object, that causes a change in the
amplitude that triggers a change in the output
state.

5. INDUCTIVE PROXIMITY SENSOR
In term of nonferrous object, when metals such
as aluminum or copper approaches the sensor,
the oscillation frequency increases. On the other
hand, when a ferrous-metal object such as iron
approaches the sensor, the oscillation frequency
decreases. This change in reference frequency
detects the sensor output signal.
Non-metallic substances such as liquids or some
kinds of dirt do not interact with the magnetic
field, so an inductive sensor can operate in wet
or dirty conditions.

6. CAPACITIVE PROXIMITY SENSOR
Capacitive Proximity Sensors detect changes in
the capacitance between the sensing object and
the Sensor.
It is similar to a capacitor with two parallel
plates, where the capacity of the two plates are
detected.
One of the plates is the object being measured
and the other is the Sensor’s sensing surface. It
detects the changes in the capacity generated
between these two poles.

7. CAPACITIVE PROXIMITY SENSOR
The capacitive proximity sensor consist a high-
frequency oscillator along with a sensing surface
formed by two metal electrodes.
When an object comes near the sensing surface, it
enters the electrostatic field of the electrodes and
changes the capacitance of the oscillator.
The oscillator circuit starts oscillating and changes
the output state of the sensor when it reaches
certain amplitude.
As the object moves away from the sensor, the
oscillator’s amplitude decreases, switching the
sensor back to its initial state.

8. ULTRASONIC PROXIMITY SENSOR
Ultrasonic proximity sensors are mainly for object
detection and distance measurement. Ultrasonic
sensors work by using sound frequencies higher
than the audible limit of human hearing (around
20 kHz), which is typically in the range of 25 to 50
kHz.
The basic physical principle of ultrasonic sensing is
that the sensor sends out an ultrasonic pulse and
receives a pulse back. Using the time difference
between the sent and received signal, the distance
to the object can be determined.

9. ULTRASONIC PROXIMITY SENSOR
Because ultrasonic proximity sensors use
sound rather than light, they can be used
where photoelectric sensors have difficulty,
such as in detecting clear plastic objects
and labels, highly reflective surfaces that
throw off optical sensors, or even liquid
levels.
They’re also immune to common
contaminants such as dust, moisture, and
ambient light.

10. MAGNETIC PROXIMITY SENSOR
Magnetic proximity sensors are used for non-contact position detection
beyond the normal limits of any inductive sensors. Magnetic sensors can
detect magnets through walls of non-ferrous metal, stainless steel,
aluminum, plastic or wood.
Mostly used sensor’s Working principles:
Variable reluctance
Reed switches

11. MAGNETIC PROXIMITY SENSOR
Variable reluctance Magnetic sensor
The variable reluctance sensor consists of a permanent magnet
and a ferromagnetic pole piece surrounded by a coil of wire.
A magnet is attached behind the pole piece, creating a magnetic
field through the pole piece and winding. This magnet projects
out from the pole piece front, also known as the sensor tip.
When ferrous material passes through and disrupts this
magnetic field, electricity (a sine wave) is generated (they are
passive devices and do not require any external source of power
to generate a signal).
The amplitude of the signal is affected by the speed of rotation.

12. MAGNETIC PROXIMITY SENSOR
Reed Switches
Reed switches are magnetically actuated switches. It
consist of two low reluctance ferro-magnetic reeds
(contact blades) sealed in a glass capsule containing
inert gas.
A magnetic field from an electromagnet or a
permanent magnet will cause the reeds to attract
each other to complete an electrical circuit.

13. OPTICAL PROXIMITY SENSOR
A Photoelectric Sensor consists of an Emitter for emitting light and a Receiver for receiving light.
When emitted light is interrupted or reflected by the sensing object, it changes the amount of light
that arrives at the Receiver.
The Receiver detects this change and converts it to an electrical output.
The light source for the majority of Photoelectric Sensors is infrared or visible light (generally red, or
green/blue for identifying colors).
Working principles:
 Through- beam optical sensor
 Reflective optical sensor
 Diffuse- reflective optical sensor

14. OPTICAL PROXIMITY SENSOR
Through- Beam Optical sensor
The sensor consists, an Emitter and the Receiver.
The Emitter and Receiver are installed opposite each
other that allows the light from the Emitter to enter the
Receiver.
When a sensing object is passing between the Emitter
and Receiver, it interrupts the emitted light, that
reduces the amount of light which enters the Receiver.
This reduction in light intensity is used to detect an
object.

15. OPTICAL PROXIMITY SENSOR
Retro- Reflective Optical Sensor
The Emitter and Receiver are installed in the
same instrument, and light from the Emitter is
normally reflected back to the Receiver by a
Reflector installed on the opposite side.
When the sensing object interrupts the light, it
reduces the amount of light received.
This reduction in light intensity is used to detect
the object.

16. OPTICAL PROXIMITY SENSOR
Polarized Reflection with Reflector Optical sensor
Its working principal is same like Retro- Reflective
sensor. It is been modified according to industrial
demand of sensing a shiny object which create
complication for Retro- Reflective sensor to identify the
product.
Modification:
Filter (fine line grid) is introduced in front of the Retro-
Reflective sensor. It is placed in Horizontal position for
Emitter and Vertical position for Receiver.
Also the reflector is made incorporating sets of three
mirrors oriented at right angles (90°) from each other
(referred as corner cubes)

17. OPTICAL PROXIMITY SENSOR
Working:
Light emitted by a light source
oscillates and meets a polarizing
filter (fine line grid), only the light
oscillating parallel to the grid is let
through. The transmitted light
oscillates horizontally until it hits
the reflector.
The corner cubes of the reflector
rotates the polarization direction by
90° and reflect the light back to the
sensor.

18. Working:
The light return passing through the vertically polarized
filter on the receiver
With the use of polarization and corner cubed reflectors,
Retro- Reflective sensors creates a closed light circuit
which ensures that light detected by the receiver was
sourced by the emitter.
OPTICAL PROXIMITY SENSOR

19. OPTICAL PROXIMITY SENSOR
Diffuse- Reflective sensor
The Emitter and Receiver are installed in the
same instrument .
When light from the Emitter strikes the sensing
object, the object reflects the light and it enters
the Receiver where the intensity of light is
increased.
This increase in light intensity is used to detect
the object.