Rabin Rajan - tue.iitm.ac.in
Transcript of 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