top five questions about thermal imaging
1) What's the Difference Between Thermal Imaging and Night Vision?
Night vision devices operate by amplifying ambient light over a thousand times (starlight or moonlight) whereas thermal imaging can operate in total darkness. If you ever have the opportunity to take a cave tour, the tour guide demonstrates "cave darkness" which is the total absence of light; it's pitch black. Night vision goggles (NVGs) don't work in this environment, but thermal imagers do. Also, NVGs can be blinded by a flashlight, while thermal imagers are entirely unaffected.
2) Does Any Tool Measure Temperature Directly?
Nope! Spot pyrometers, thermocouples, thermometers, and thermal imagers measure the effects of heat transfer (voltage, pressure, etc.) caused by heating and cooling but are worthless without calibration.
3) Can Thermal Imagers See Through Walls or Tree Canopy?
No-go, soldier! Most thermal imagers are passive sensors, meaning that they only "see" energy reflected or emitted from the surface of objects. Active sensors like LiDAR, RADAR, Microwave, and Radio send a pulse of energy from the sensor at varying wavelengths and measure the radiation received from that object. Some active sensors can see through tree canopy and walls.
4) Can I field check the calibration of my thermal imager?
Absolutely! You can do a quick field check using a bucket of crushed iced water. Head to your local drive-in burger stand and get a few large cups of crushed ice (with the obligatory hot dog). Pour that crushed ice into cold water, wait a minute or two then measure the temperature of that water using your thermal imager. If the temperature is within a degree of 32 degrees Fahrenheit (0 degrees Celcius), then your imager is working correctly. You can perform a two-point check using a pot of boiling water, but not many folks care to carry a heating element to the field. If you are one of those ready-for-anything, "of course I have my camp stove" type of people, then image a pot of boiling water, and if the temperature reads on or about 212 degrees Fahrenheit (100 degrees Celcius) then you are A-OK!
5) How do I pick the right thermal imager?
Picking the right tool for the job is critical in any field. When picking a thermal imager, there are 3 main things to take into account:
1) Frame Rate - Are you imaging a high-speed production line at 2000 frames per second? No? Then you don't need a photon counter. Microbolometers can capture at 9Hz and 30Hz; the only difference is whether you want smooth video or not. A 30Hz sensor captures a smooth video of moving targets.
2) Wavelength - If you are imaging a furnace through an infrared window and need to see past the flames to measure the temperature of the furnace tubes, then you need a cooled, mid-wave (MWIR) sensor. If you are monitoring the temperatures of electrical equipment or building facades, then you need an uncooled, long-wave (LWIR) sensor.
3) Distance to Target - Some applications do not allow for imaging within a certain distance of the target. In those cases, you have two choices:
a) Increase the focal length of the lens - the longer the focal length, the closer the object appears to the imager, but the field of view decreases (it's a trade-off)
b) Increase the resolution of the sensor - jamming more pixels into a detector array will not only give you greater analysis power but allows you to be further away and still get plenty of pixels on target.
You can also go with secret option "c" and do BOTH!