Rabin Rajan - tue.iitm.ac.in

Rabin Rajan 30-05-2015

A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.

The maximum distance that this sensor can detect is defined "nominal range". Some sensors have adjustments of the nominal range or means to report a graduated

detection distance

Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object.

A proximity sensor adjusted to a very short range is often used as a touch switch

All sensors performing non contact sensing are included in proximity sensors

http://en.wikipedia.org/wiki/Proximity_sensor

Proximity

Sensors

Inductive

Capacitive

Ultrasonic

Optical

Reflective

Direct

Retro

Reflective

Polarized Reflection with

reflectorThru Beam

Sensor types

https://www.pc-control.co.uk/Inductive.htm

Inductive proximity sensors

Inductive sensor uses changes in an electromagnetic field, so the target must be must be metal.

Advantages

• Accurate• High switching rate• Works in harsh environmental condition

Disadvantages

• Detects only metallic target

Applications

• Metal detectors• Automobile industry

https://manish516.wordpress.com/2012/11/04/for-automation-in-the-industry-what-are-the-different-types-of-proximity-sensors-used-and-how-do-they-works/

Capacitive proximity sensors Detects metallic objects as well as non-

metallic objects(liquid, plastic, wooden material etc)

Uses variation of capacitance between sensor and object

Distance down to 1 micro inch can be measured

All targets having dielectric constant more than air can be detected

Advantages

• Metallic & non-metallic targets• High speed• Good stability• Low cost and power consumption

Disadvantages

• Affected by temperature and humidity• Less accurate• Difficult to design

Applications

• Mobile Phones • Laptop track pads and more

http://www.ceasiamag.com/article/developing-detection/5759

Ultrasonic proximity sensorsUses ultrasonic sound wave for detection

Used frequency is higher than audible range

Can measure distances very accurately

Provides good sensing for large objects with hard surface

Advantages

• Not affected by atmospheric dust, snow, rain etc.• Sensing distance more than capacitive and inductive Sensors• Works in adverse condition

Disadvantages

• Difficult to sense from soft, curved, thin or small objects

Applications

• Ultrasonic thru beam sensors in bottle counting machine

• Vehicle detection in barrier systemhttp://www.engineershandbook.com/Components/proximitysensors.htm

Optical proximity sensors

Senses any object within 10 meters range

Uses an LED in either infrared or visible light spectrum to transmit

Photodiode detects the light generated

Generally light sources pulse the infra-red light on and off at a fixed frequency.

Sensor detects object when it disrupts light beam

Two types- Reflective type And Thru beam type

• Thru Beam type

Emitter and receiver housed separately

Object is detected when light beam is disrupted

Allows the longest range

• Reflective type

Emitter and receiver are housed together

Object is detected by means of reflection

Three types

1. Direct reflection

2. Reflection with reflector

3. Polarized reflection with reflector

Advantages

• Effective in dusty environments• Focused beam• Higher sensing distance• Immune from interference

Disadvantages

• Expensive

Applications

• Lift door mechanisms• Components positioning sensing• Security & safety •Counting objects in conveyer belts

http://www.ab.com/en/epub/catalogs/12772/6543185/12041221/12041223/Retroreflective-and-Polarized-Retroreflective.html

History of proximity sensors

Invented in 1958 at Mannheim laboratory by Walter Pepperl and his colleague Wilfried Geh . It was originally conceived as a customer-specific solution for an intrinsically safe current circuit in the chemical industry.

Chemical plant

Automobile industry

All kinds of industry

http://www.controlengeurope.com/article/20839/Fifty-years-old--the-proximity-switch.aspx#

A few applications

Vibration measurements of rotating shafts in machinery

Parking sensors, systems mounted on car bumpers that sense distance to nearby cars for parking

Ground proximity warning system for aviation safety

Sheet break sensing in paper machine.

Roller coasters

Top dead centre (TDC)/camshaft sensor in reciprocating engines

Conveyor systems

Mobile devices Touch screens that come in close proximity to the face Attenuating radio power in close proximity to the body, in order to

reduce radiation exposure