Thermal Imaging Cameras

Compare THERMAL IMAGING CAMERAS. A thermal imaging camera displays the thermal image of the item being observed, Thermal imaging cameras are also known as forward looking infrared (FLIR) imagers because they display the infrared (IR) image of any item. Thermal imaging cameras are used in industry in a predictive maintenance program to monitor the temperature of critical points on equipment. Thermal imagers also help firefighters to locate living bodies in smoke filled rooms.

Thermal imaging cameras use uncooled microbolometers to sense infrared radiation. The uncooled microbolometer was developed by the military and first used in thermal imagers about 20 years ago. They are now standard due to their low cost and weight compared to other types of bolometers.  The microbolometer is an array of IR sensitive pixels that is similar to a digital camera. The most common array sizes for thermal imagers are 320 x 240 pixels and 160 x 120 pixels.

The image in thermal imaging cameras is displayed through a viewfinder or an LCD screen at a frame rate of 30 - 60 Hz similar to a TV signal for most models of thermal imager. The field of view (FOV) with standard optics is in the 23 - 27 degrees x 17 - 20 degrees range. The focus ranges from 12 inches to infinity and focusing can be manual or automatic. A laser pointer to help aim the thermal imaging camera is standard on many models. Also, all models have some memory for image storage. These images may be JPEG format and transferred on a flash memory card or by USB or Ethernet cable to a PC. All models of thermal imager are battery powered with rechargeable batteries with a battery life from 2-1/2 to 5 hours. Some also operate with an AC adapter.

Infrared is the region beyond red light, approx 0.75u (micron) to more than 15u wave length. This is the spectral range for most thermal imaging cameras the thermal sensitivity for microbolometer arrays range from 0.05 to 0.08 C at 30C and 30Hz. This is a reference given for comparison of different models. The temperature range typically ranges from -40 C to 600 C. A reading range usually is about 150 to 200 C. Many models come with 2 or 3 temperature ranges standard. Some models have optional temperature ranges up to 2000 C. The reading accuracy for most microbolometer imagers is +/- 2 C or +/- 2% of reading.

Every object emits electromagnetic waves in the infrared region. The amount of thermal energy emitted depends on the temperature and the material properties of the object. The ability of any material to emit infrared waves is called the emissivity. Perfect emissivity is 1.0 and is called a blackbody. Most materials have an emissivity of less than 1.0 and more than 0.0. To make an accurate temperature measurement, the emissivity of the object must be known. It is a variable that must be entered into most thermai imaging cameras. Some use an emissivity of 0.95 to calculate the temperature of measured objects