While I generally combine the last 2 days of class together due to studying for a test, general lack of items to discuss, etc… I don’t think that will be an issue here. So onward to day 4, and seeing that day 3’s trivia went unanswered – you will have to wait for Day 5 to get the answer. Speaking of the trivia question… Talk about a fun way to start a day… walking in, hearing the conversation stop & then the instructor say, we were just discussing you… Shoot, my “secret” was out, but while talking about it, he did mention that the 10 times may not fully be accurate as it also depends on the type. (so there is another hint)
For anyone taking any class, I have to recommend you do the homework & not trying to slide by. If you try doing that with Van, you will be in trouble as he does go around the table & has you not only read the question, but work it out & give your answer. Not only is that one good reason, but it also helps you make sure you understand the material and have the correct answer based on the right reasons (insert whistling smillee here – yep I had them all correct, but 2 of them on the IFOV were for the wrong reason – whoops). As a quick FYI, the homework primarily involved calculating IFOV, the RAT, and converting temperatures.
Thermal Capacitance, Diffusivity & State Change:
After finishing off the homework review & doing some work with our cameras, we moved back to the book to cover a few sections we had skipped earlier. The first section covered thermal capacitance or how much heat specific items can hold which can help us diagnose issues like roof leaks. For a typical “flat” roof, we can diagnose the leak because dried out foam behaves differently than foam that has absorbed water.
We next moved into diffusivity which explains how heat entering an item, moves through it. The easiest example is if you drop some food coloring in a gallon of water & watching how it spreads out, or a drop of oil in water – both react differently based on the mediums much like different materials we run into daily.
The very last section covered state changes, or how materials can exist in various states (gas, solid, & liquids). This is important to understand especially if you are involved with steam, dew points, and electrical components (especially in regards to Arc-Flash)
Getting an Accurate Temperature / Emissivity Value for an unknown material:
- Before starting for the day you need to complete a FFT (Field Functionality Test Check) or a calibration test
- The material needs to be at a steady state temperature with a known emissivity material being attached to it (Electrical tape work well in many cases – emissivity is .95)
- You need to be able to control / manage the background temperature or anything that may affect it (i.e. a tarp, piece of paper, wall, etc…) The back ground equates to where any reflection that may affect the receptors is coming from (see black box below for just how tough that can be)
- You need to set the camera to the proper background temperature – using 1. As the emissivity value
- Reset your camera to .95 (or known value – see 2nd item above) & get temperature from known point.
- Using the camera move over to the unknown material & snap a quick picture. Depending on your camera you may be saving it & or working with a frozen image & changing the emissivity value to raise the area in question to the temperature of the known point.
- You know have a known emissivity value for that item and an accurate temperature for that point in time based on your camera’s accuracy
- At the end of the day you should complete another FFT or a calibration test
The Practical Portions of the Test:
The practical test is composed of 3 parts- the third part I cannot, nor will I discuss. The first two parts have been discussed earlier, but they are quite simple (especially with a great camera – I love my Fluke Ti32 as compared to the loaner I had for the 1st class). I first started off with the required FFT, and then moved onto the “Accurate” Temperature portion (see above). Once that was completed I moved onto the black box which actually took more time than the temperature portion. For the black box, you are required to snap 4 pictures;
- The top section should show 4 items with different temperature values (no trick as they all should be 4 different temps) — Van’s recommended selection is the rainbow palette
- The center section requires a picture of the mix of large & small dots & lines. — Van’s recommended selection is Gray Scale / I just stayed in Rainbow
- The final section contains 3 dots, with one having a reflector on it – you need to snap 2 pics in the same palette with the reflection appearing hot & then cold. — No recommended palette & I would dare say this is the trickiest part trying to get the reflection lined up correctly for the hot reflection.
Once you are done with those, you complete one more FFT, and get to go see the instructor. After completing the final test and clearing the camera you get your score. Hopefully you get to go, sweet I nailed it and now I can relax… well that is until you remember that you have two more tests the next day, after 1 final pop quiz & section in the book… (Yeah, I nailed it – 100% baby)