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photo:thermal_imaging

thermal imaging cameras

Introduction

  • near IR night vision cameras are very different to thermal imagers and detect reflected near IR light in wavelengths shorter than 1µm (eg. 850 or 940nm IR lamps) or heat sources 250-500degC which give heat off in this wavelengths
  • thermal imaging cameras do NOT use IR lamps for imaging but detect the longer long wave mid-IR wavelengths (usually 7-14µm) that are given off by objects and animals with the wavelength dependent upon the object's temperature and use a microbolometer
  • these microbolometer arrays are commonly found in two sizes, 320×240 pixels or less expensive 160×120 pixels hence the images are very low resolution, but the ideal is the much more expensive 640×480 pixel sensors
  • the standard commercial models are non-cooled microbolometer sensor arrays are usually vanadium oxide (VOx)
  • there are very expensive and heavier cooled devices which give much further range and are primarily used by the military
  • most are manual focus
  • they are primarily used for:
    • detecting warm blooded animals including humans day or night
      • however, in general, all one sees is the shape - there is very little detail - so once can identify what type of animal it is and see how it is behaving, but unless reasonably close, it is unlikely that detail is sufficient to recognise who it is
      • cold blooded animals will generally be camouflaged thermally with its surroundings and are thus generally hard to visualise
    • detecting temperature differences on objects
      • areas of heat loss / poor thermal insulation / water leaks
      • areas of excessive heat / poor electrical wiring, etc
    • measuring temperatures without contact:
      • 8–15 μm wavelengths equates to 89°C down to −80 °C
      • 3–8 μm wavelengths equates to 693°C down to 89 °C
      • higher end Flir cameras generally have a range of 400°C down to minus 20°C
      • a body radiates heat in various frequencies of e-m radiation, and its peak frequency becomes higher in proportion to the temperature of the body and can be calculated from Wien's displacement law:
        • peak wavelength radiated in microns = 2897.2/(temperature in Kelvin)
        • however, accuracy of temperature measurement requires understanding:
          • the thermal emissivity coefficient for that object as very few objects act as black body objects and physical objects will have an emissivity of between 0.01 and 0.99 and thermography is likely to be extremely inaccurate if the object has emissivity less than 0.5
            • some thermal emissivity coefficients:
              • highly polished metallic surfaces such as copper or aluminum usually have an emissivity below 0.10
              • gravel, galvanised steel 0.28
              • styrofoam, stainless steel, roughened or oxidized metallic surfaces will have a much higher emissivity of around 0.6
              • fibreglass 0.75
              • cardboard 0.81
              • hardwood across the grain 0.82
              • snow 0.85
              • perspex 0.86
              • plaster 0.86-0.90
              • flat-finish paints are around 0.90
              • red bricks, PVC 0.92-0.93
              • glass, concrete, heavily rusted iron 0.92-0.95
              • food and organic materials, rubber, ice 0.95-0.97
              • standard black insulation tape has an emissivity of about 0.97
              • human skin, water and asphalt are about 0.98
          • other potential errors in thermography measurements:
            • reflection from the object of a nearby heat source especially if the object has low emissivity
              • some thermal cameras allow you to enter the object's emissivity and the ambient temperature and will adjust the readings to allow for reflection of this ambient temperature as well as the object's emissivity
    • use in medicine:
      • detect skin temperature from a distance as a method of screening for febrile people
      • monitor breathing rates
      • detect inflamed ankles
      • detect increasing mental workloads by reductions in facial temperatures especially around the nose
      • detect emotional states:
        • passion increases temperatures around the hands and face
        • empathy decreases temperatures, especially in the nose
      • assess skin / muscle inflammation including injuries
      • assess peripheral vascular disease
    • use in camping / hiking
      • search and rescue - finding an unconscious hiker is made so much easier with a thermal imager
      • wildlife - searching for often well camouflaged and nocturnal animals to observe their behaviour or to photograph them at twilight with your usual telephoto camera
      • camping safety at night - be on the look out for predators - human or animal
    • driving assistance at night or in fog
      • can better identify people or animals and can see through oncoming headlight glare

thermal imaging devices for outdoor use - search and rescue, hunting, hiking

thermal imaging devices for scientific or industrial use

attachments to smartphones

    • USB-C connection for Android phones; up to 384×288, 17micron, 25Hz, <60mK; measures temps minus 20degC to 120degC (Pro version extends to 400degC)
    • 384×288 17 μm, 25Hz, <60mK; 89g; temperature range of -20℃ - +120℃ but can extend to 400degC; 4 hours using one CR123 battery; 13mm lens 23.6°×20.7° fov;
    • $AU1394
  • GUIDE MobIR Air CB360 smartphone attachment fever screening device Android only?
  • GUIDE MobiIR Air android only?
      • 160×120 19200pixels 25Hz < 40mK; 26g; minus 20 to 350°C temp measurement ±2°C accuracy; up to 3 spots; 7 color palettes;50° × 38° fixed focus; Android phones only
      • less temp range but more accurate temp measurements ±0.5°C a 30-45°C; ±2degC 5-30°C and 45-100°C; 26g; 50° × 38° fov; fixed focus; Android phones only
    • thermal image resolution 160×120 = 19,200pixels = 0.019Mp with 8 — 14 µm spectral range
    • Thermal Sensitivity [MRDT] 70mK; frame rate 8.7Hz;
    • angle of view 50° x 43°
    • output image with optical overlay is 1440×1080 with close focus to 0.3m
    • file formats: Radiometric JPG, MPEG-4 (file format MOV)
    • phone app can give Hottest, Coldest and 3 spot temperature measurement with ±3°C or ±5% accuracy and range -20˚C to 400˚C
    • battery life 1hr charges via Female USB-C in 40min
    • 68 × 34 × 14 mm (2.7 × 1.3 × 0.6 in) and weighs 36.5g
    • $AU630
    • similar to Pro model but:
      • thermal image resolution 80 × 60 = 4800 pixels and range is only range -20˚C to 120˚C
      • Thermal Sensitivity [MRDT] 100mK
      • angle of view 50° x 38°
    • $AU499
    • similar specs to FLIR One Pro LT but:
      • Thermal Sensitivity [MRDT] 150mK
      • cannot switch between thermal, visual, and combined MSX views
    • $AU439?

medical

industrial

    • 3“ 320 × 240 color LCD display
    • thermal image resolution 160 × 120 pixels, close focus 0.5m
    • spectral range 7.5–13 µm
    • FOV 45° × 34°
    • Thermal Sensitivity 100mK
    • measurement accuracy ±2°C (±3.6°F) or ±2% of reading with object temp range –20°C to 400°C
    • rechargeable 3.6 V Li ion battery gives 4hrs use and takes 2-2.5hrs to charge
    • 640 × 480 jpeg output no video
    • $AU2365
    • as for E5-XT WiFi but twice the resolution and sensitivity and twice the price:
      • thermal image resolution 320 × 240 pixels
      • Thermal Sensitivity 50mK
    • $AU5165
photo/thermal_imaging.txt · Last modified: 2021/09/03 16:12 by gary1