Your THERMOGRAPHY COMFORT LEVEL – Equilibrium is your enemy. Recognize it! Avoid it!
Thermal imaging cameras can be used to locate unfilled cinder blocks. The principle is thermal capacitance. In the above images I used my Fluke IR Fusion camera at 7am, 10am and 2pm. In the winter the sun rises in the east and travels more in a southern route and then sets in the west. These images are of a south wall and, as you can notice, at 7am there is no solar influence. At 10am you can see the shadows from a tree along with the effect of solar influence. And at 2 pm we have full solar impact. What if you had inspected this wall only one time, at 10am? What would have been your conclusion? Since air has a lower thermal capacitance than filled cinder block the unfilled blocks will change temperature faster. After a cool night in Sacramento the unfilled blocks are cooler than the filled blocks. By 10 am they have reached equilibrium. By 2 pm the temperature of the unfilled blocks has risen above the filled blocks, all due to the principle of thermal capacitance. An important lesson in this experience is to realize that equilibrium will be reached twice in a 24 hour period. For this type of investigation you will do better with a more sensitive detector system, a 70mK or 50mK detector. The Fluke TiR1 has a 70mK detector array; the Fluke TiR27/Ti27 has a 45mK/50mK detector array; the Fluke TiR29/Ti29 has a 45mK/50mK detector array and the Fluke TiR32/Ti32 has a 40mK/45mK detector array. These images were taken with the 70mK detector.
Whether you are looking for moisture signatures in flat roofs or liquid levels in water tanks, be aware that equilibrium occurs twice in a day and it truly Is your enemy. Always ask the question: Has my target reached equilibrium?