Theory of night vision
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Theory of night vision

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Theory of night vision Theory of night vision Presentation Transcript

  • By NS Wickramasinghe BSc (Eng) 1/19/2014 1
  • CONTENTS         INTRODUCTION HISTORY GENERATIONS OF NVDs BASIC WORKING PRINCIPLE IMAGE INTENSIFIER TUBES BASIC COMPONENTS MAINTENANCE OF NVDs NIGHT VISION DEVICES USED IN SRI LANKA NAVY
  • INTRODUCTION  HUMAN VISION IS COMPACKED TO VISIBLE RANGE.  ELECTROMAGNETIC SPECTRUM .  ENHANCED SPECTRAL RANGE TECHNIQUES USES TO VIEW INVISIBLE THINGS.  ENHANCED SPECTRAL RANGE ALLOWS THE VIEWER TO TAKE ADVANTAGE OF NON-VISIBLE SOURCES OF ELECTROMAGNETIC RADIATION
  • NIGHT VISION TECHNOLOGIES USED  IMAGE ENHANCEMENT  THERMAL IMAGING
  • IMAGE ENHANCEMENT  COLLECTS THE TINY AMOUNTS OF LIGHT .  INCLUDES THE LOWER PORTION OF THE INFRARED LIGHT SPECTRUM .  AMPLIFYING IT TO THE POINT THAT WE CAN EASILY OBSERVE THE IMAGE .
  • THERMAL IMAGING  CAPTURES THE UPPER PORTION OF THE INFRARED LIGHT SPECTRUM.  IR EMITTED AS HEAT BY OBJECTS INSTEAD OF SIMPLY REFLECTED AS LIGHT .
  • INFRA RED 1/19/2014 7
  • INVENTION OF NIGHT VISION  “SEEING WITHOUT BEING SEEN” IT IS THE BASIC TACTIC OF ANY MILITARY FORCE IN THE WORLD.  NIGHT VISION SERVES FOR THAT PURPOSE.  NIGHT VISION DEVICE INVENTED BASICALLY FOR MILITARY USE.  SCIENTIFIC / CIVILIAN USE SOMETIMES LIMITED OR EVEN FORBIDDEN BY LAW 1/19/2014 8
  • HISTORY / FUTURE OF NVDs  1930’S - IMAGE CONVERTER TUBE – Basis for NVDs  LATER NVDs WERE CLASSIFIED AS PER THE DEVELOPMENT STAGE OF USED IMAGE INTENSIFIER TUBE (IIT) , AS GENERATION OF NVD  GENERATION 0,1, 2, 2+, 3  GENERATION 4 (ONLY IN US) 1/19/2014 9
  • SPECTRUM OF NVDs  NIGHT VISION MONOCULARS/ BINOCULARS  NIGHT VION WEAPON SIGHTS  NIGHT VISION GOGGLES  LONG RANGE NIGHT VISION 1/19/2014 10
  • HOW NIGHT VISION WORKS 1/19/2014 11
  • ARRANGEMENT OF UNITS IN NVD 1/19/2014 12
  • 1/19/2014 13
  • HOW NIGHT VISION WORKS  AN OBJECTIVE LENS (CONVEX TYPE) FOCUSING AN IMAGE INTO A VACUUM TUBE WITH A PHOTOCATHODE AT ONE END  IT RELEASES ELECTRONS BY THE PHOTOELECTRIC EFFECT ON THE INCIDENCE OF INCOMING PHOTONS.  FROM THERE, THE PHOTOELECTRON IS ACCELERATED THROUGH AROUND 5000 VOLTS INTO A TILTED MICROCHANNEL PLATE.  THE HIGH ENERGY ELECTRON RELEASES SOME MICROCHANNEL PLATE ELECTRONS, WHICH FURTHER RELEASE OTHER ELECTRONS, IN A PROCESS CALLED SECONDARY CASCADED EMISSION.  THE MCP IS TILTED TO ENCOURAGE MORE ELECTRON COLLISIONS 1/19/2014 14
  • FOM  FIGURE OF MERIT OF A NIGHT VISION DEVICE  IT’S A MEASURE OF THE QUALITY OF THE IIT FOM= RESOLUTION X SIGNAL TONOISE RATIO (S/N)  GEN 3 – APPROX 1600 FOM 1/19/2014 15
  • IITs IN NVDs 1/19/2014 16
  • 1/19/2014 17
  • GENERATION 0  SO LITTLE, LOW LIGHT AMPLIFICATION  ADDITIONAL IR –ILLUMINATORS MUST BE USED FOR OBSERVATION. (THAT’S WHY , THEY ARE CALLED ACTIVE NIGHT VISION DEVICES )  IMAGE CONVERTER TUBE WAS USED, NOT THE IMAGE INTENSIFIER TUBE. 1/19/2014 Cont … 18
  • Cont … • S-1 photocathode, coated with silver shifted cesium oxide • Anode cone, ensures over high voltage acceleration focusing and turning the image up-side-down • P1 phosphor screen, coating out of zinc and cadmium transferred phosphor 1/19/2014 19
  • GENERATION 0 -DISADVANTAGES  HAD A VERY DISTORTED PICTURE  SHORT TUBE LIFE DUE TO THE HIGH ELECTRICAL VOLTAGE.  HEAVY AND BIG POWER SOURCE  AN AUTOMATIC PROTECTION OF THE PHOTOSENSITIVE TUBE DOES NOT EXIST 1/19/2014 20
  • GENERATION 1 1  IMAGE INTENSIFIER TUBE USED FOR THE ST TIME (WITH MULTI - ALKALI PHOTO CATHODE - S-20, coating from potassium, sodium, cesium, silver)  LUMINOUS GAIN BETTER THAN GEN. 0 (P-20 phosphor screen)  SERVICE LIFE OF GEN 1 IIT- 1000-2000 HRS  NO AUTOMATIC PROTECTION AGAINST BRIGHT LIGHT  WORKING RANGE 750-800 nm OF IR WAVE LENGTH 1/19/2014 21
  • Cont … Sectional view Gen1, singlestage NVD, low gain Sectional view Gen1, 3-stage NVD, generally high gain at low contrast 1/19/2014 Cont … 22
  • GENERATION 2  MICRO CHANNEL PLATE (MCP) USED IN IIT INSTEAD OF ANODE CONE.  PRINCIPLE CHANGED FROM ACCELERATION  MULTIFICATION (electrons)  THE LIFE SPAN INCREASED TO APPROX. 2500 - 5000 H  WORKS WITHIN THE RANGE BETWEEN 780 AND 850 NM WAVELENGTH 1/19/2014 23
  • STRUCTURE OF IIT ND (2 GEN)  PHOTO CATHODE  MICRO CHANNEL  PHOSPER SCREEN 1/19/2014 24
  • ADVANTAGES OF ND 2 GEN NVD  NO IR-ILLUMINATOR NEEDED  SMALLER IN DIMENTION  LOW IN WEIGHT  LIFE SPAN OF IIT - 2500- 5000 HRS  AUTOMATIC BRIGHTNESS CONTROL (ABC)  HIGH IMAGE RESOLUTION THAN EARLY GENs. 1/19/2014 25
  • GENERATION 2+ (SUPPER GEN)  MORE IMPROVED MCP  OVER 4 MILLION MICRO CHANNELS  PHOTO CATHODE-MORE SENSITIVE TO IR 1/19/2014 26
  • GENERATION 3  NEW COATING FOR PHOTO CATHODE – Ga As (Gallium Asernic)  IMPROVED IMAGE RESOLUTION  6-12 MILLIONs OF MICRO CHANNELS IN MCP  AN THIN ALUMINIUM LAYER ON THE PC (ION BARRIER) IS USED FOR AN ENHANCED SERVICE LIFE SPAN OF IIT- 10000 HRS  IR WAVE LENGTH- 780-920 µm 1/19/2014 27
  • GENERATION 4  FILMLESS OR THINFILM TUBES IS USED  ONLY USED BY US ARMED FORCES  15000 HRS OF LIFE SPAN 1/19/2014 28
  • GEN 1 1/19/2014 GEN 2 GEN 3 29
  • LENSES USED IN NVD CONVEX LENSES 1/19/2014 30
  • LENSES IN LONG RANGE NVDs CONVEX LENS 1/19/2014 31
  • PRISMS USED IN NVD 1/19/2014 32
  • BATTERY COVER 1/19/2014 33
  • DAY LIGHT COVER 1/19/2014 34
  • DAY LIGHT COVER 1/19/2014 35
  • EYE GUARD 1/19/2014 36
  • TYPE OF BATTERY USED IN NVDs  SIZE AAA  SIZE AA  SIZE 9V  LITHIUM 3V 1/19/2014 37
  • ‘O’ RINGS 1/19/2014 38
  • CARING CASE 1/19/2014 39
  • MAINTENANCE  SHOULD NOT OPERATE AT BAD WEATHER  MUST NOT OPERATE AT DAY TIME  KEEP NIGHT VISION BINOCULER CLEAN  CLEAN LENS WITH 99% ETHIL ALCOHOL  SHOULD NOT DROP DOWN  SHOULD NOT COLLIED WITH ANYTHING 1/19/2014 40
  • Contd.  MUST NOT APPLY GREAS OR OIL ON LENSES  THE N/V BINOCULER HAS TO BE IN THE CARRING CASE WHILE MOVING/TRANSPORT  REMOVE THE BATTERY BEFORE STORED.  STORED IT AT COOL /DRY PLACE. 1/19/2014 41
  • Night vision devices are dependent on every little light information available The task of the objective lens to collect as much as possible light and to focus an image on the image intensifier tube's input window Tube can strengthen only the low light passed and collected by the objective lens Appropriate tuning between the optical and electronic part should be take place 1/19/2014 42
  • PHOTOELECTRIC EFFECT 1/19/2014 43
  • MICRO CHANNEL PLATE 1/19/2014 44
  • 1/19/2014 45
  • 1/19/2014 46