Thermal Imaging Cameras and Temperature

I’m currently working on a project for a company to look at the heating behavior of certain materials and I ran into some fundamental misunderstanding of how thermal imaging cameras work from the company. Sounds like a great topic for a blog posting, if you ask me.

First off, thermal imaging cameras do not measure temperature. Of course, most temperature measurement tools don’t measure temperature directly either. A bulb thermometer, like those your mom used to stick under your tongue, measures the volume of a fluid such a mercury or alcohol which changes due to thermal expansion.

If you have a digital thermometer, it probably has a thermistor in it, which is a type of resistor whose resistance varies with temperature.  The thermometer you stuck in your turkey for Thanksgiving most likely has a bimetallic strip inside it, which turns the needle on the temperature dial.

The bimetallic thermometer has two strips of different metals that are joined together.  The metals expand at different rates when heated, causing the strip to curl as it heats up, thus turning the temperature needle.

Infrared thermometers use the same technology as infrared cameras.  Both measure the infrared light emitted by an object.  (Pet Peeve Alert:  An infrared laser thermometer does not use a laser to measure temperature.  The laser is just a guide so you know where the thermometer sensor is pointing).  All objects emit some infrared light due to their temperature.  This is referred to as black-body radiation (it’s called “black-body” because the light coming from a perfectly black object that doesn’t reflect any light would only be the black-body radiation).

The filament in an incandescent bulb is an example of a black-body (actually this is only an approximation, but it works for our purposes).  The more you heat up the filament the brighter it gets.  If you have any incandescent bulbs on a dimmer switch you can see this effect.  The reason that these bulbs are so inefficient (and the reason they are so darn hot) is because they are dumping a lot of energy into the infrared part of the spectrum that our eyes can’t see.  If you continued to heat the bulb up even higher you would eventually start to get some ultraviolet light as well (which isn’t so great).  This is why halogen bulbs, which do get hotter than incandescent bulbs, have ultraviolet filters on them.  For objects at typical human temperatures, the light emitted is in the infrared part of the spectrum.

The way the infrared camera works is that it converts the intensity of infrared radiation emitted by objects into an electric signal, which is converted into a colored pixel on the display.  You should end up with something that looks like this:

Haunted Basement? Elmo and Joy hang out in IR

There is one slight problem with this image.  Everything except Elmo and Joy (the glowing evil spirits that haunt my basement) are all at the same temperature as the room, but we can clearly see the boxes (can you spot the litter box?) and chair in the background.  What gives?  The reason we can see these objects, even though they have the same temperature is because they have different emissivities.  This means that have different “brightnesses” in the infrared.  Ironically, something that we see as black usually has a fairly high emissivity while something that is white to our eyes probably has a much lower emissivity and will appear “cooler” in the infrared than it really is.  The type of material and the thickness of the material can also affect the infrared light emitted so a sample of wood, plastic, and metal, all at the same temperature would look different in the infrared part of the spectrum.

So the problem with using a thermal imaging camera (or any infrared thermometer) is that you need to know something about the surfaces you are looking at.  To understand this point a little more clearly, take a look at the black-body radiation curve below.  The camera detects the infrared light near one particular wavelength.  In this graph here I’ve chosen the 2.0 μm wavelength (vertical line).

When the camera detects a particular intensity of radiation (say one of the points circled in red) it associates that intensity with a particular temperature curve.  If the camera detected an intensity of 2.0 (in arbitrary units displayed on the graph) it would say “aha, that looks like it belongs to the 6000 K curve for a black-body” so it reports a temperature of 6000 K (roughly 5727° C).  If the object the camera is looking at has a lower emissivity than the camera thinks (i.e. the object isn’t as bright in the infrared as its temperature would indicate) the actual temperature of the object would be much higher.  To go back to our incandescent bulb, imagine we are trying to determine how hot the filament is by measuring the brightness of the filament.  If the bulb is heavily frosted, the filament looks dimmer than it really is so we would think the filament is cooler than it actually is.  To determine the real temperature of the filament we would need to know something about how much light is blocked by the frosted bulb.  In infrared thermometry, the emissivity of the object takes the place of the amount of frosting on the bulb.

There is one other complication with measuring temperatures using an infrared camera.  Many surfaces are highly reflective in the infrared, so the infrared radiation you detect may not  be emitted by the surface, but may be a reflection from something else.  Notice Elmo’s reflection in the floor under him in the picture below.

Elmo hiding from the dogs

The camera thinks the floor in front of Elmo is much hotter than it really is because of his infrared reflection.  When you start making measurements of shiny metals, which have much lower emissivities (they tend to look much darker than their temperature would indicate) and higher reflectivities, and it becomes very difficult to accurately measure temperatures.  The reflection of the room temperature camera appears much brighter than a very hot piece of metal.

The idea of using infrared thermometers brings up another pet peeve of mine.  Students tend to think that tools that are more high-tech tend to be better than their lower-tech cousins.  This isn’t true and frequently the lower-tech devices are better.  To measure a temperature I’ll take a thermistor or thermocouple any day of the week.  Now that isn’t to say that infrared thermometry isn’t a very cool and very powerful tool, but it has its place. A great use for infrared thermometry is situations where a thermistor wouldn’t withstand the heat, like in a kiln, or when measuring temperatures over larger areas, like trying to find heat leaks on the outside of a house.  I’m sure there are many other uses I can’t think of.  Here is my “take-away” message for you: choose the simplest tool possible that gets the job done right.  Bells and whistles are cool (and believe me, this infrared camera is really cool), but more complicated tools come with a lot of built-in assumptions you might not be aware of.

Ellie takes a break from playing with her toy

 

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Current Learning Objectives for University Physics I and II

My colleague, Marlann Patterson, was kind enough to allow me to share her learning objectives for E&M. This is only her second semester using Learning Objectives Based Assessment so she is still tweaking them. I’ve also shared the current iteration of my learning objectives as well. I’ve made some changes since last semester. My first chapter is chock full of learning objectives, but I feel they are all very basic skills that students tend to not focus on. I wish I had more A-level learning objectives, but I couldn’t come up with any advanced skills that would fit nicely into the curriculum. If you end up using either of these sets of learning objectives we’d love to hear how they worked and learn what improvements you’ve made.
I’d like to point out that these learning objectives are based on something put together by Frank Noschese, who based his on a list of chapter topics put together by Robert Beichner.

Here is a link to Marlann’s current version (as of Fall 2012) of learning objectives for E&M in the 3rd edition of Matter and Interactions: Google Spreadsheet Link (each chapter has its own tab).

Here are my less organized learning objectives for mechanics in Matter and Interactions: Google Spreadsheet Link

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The Six Stages of LOBA

Stage 1: Ecstatic

Wow, I’ve finally found a grading system that makes SENSE! An it matches with what I believe. This is the BEST THING EVER!

Stage 2:  Confusion

Uhhhhhh, how do I get started, what learning objectives should I use, what should I do for assessments, won’t students  blow off the assessments and wait to reassess?

Stage 3: Quivering ball of nerves

Oh crap, my students are doing any homework, they aren’t reading, they aren’t even reassessing.  This is going to blow up in my face, I just know it.

Stage 4:  Outright Fear

Oh nooooooo, most of my students are going to fail and then I’m going to get fired.  Is it too late to go back to using points.  I’m going to have to tell all these irate parents why little Jonny and Jessie failed my class.

Stage 5: Cautious Optimism

Hmmmm, they seem to be getting the hang of this.  I’ve even got a few students on track to get A’s.  I think they are learning.

Stage 6:  Exhausted Happiness

Oh thank god it’s over.  I gave out a lot of A’s, but they all earned them.  They really seem to have learned the material for once.  But next time, next time I’m doing things better so I don’t spend so much time grading.  Is it time for break yet?

PS:  Right now, most of us at Stout are in stage 4.

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Python + Excel = Gradebook Happiness

I’m really trying to streamline my workflow (and reduce grade entering errors) so I thought rather than writing scores by hand on each assessment, I’d put the scores directly into a spreadsheet.  In order to hand back scores for each assessment, each student would need to have a separate Excel worksheet, which could be printed out and attached to the original assessment. I’d also need a way to get a master list of student scores that I can copy and paste directly into my main workbook.  If you’ve worked with Excel you can guess where I was headed at this point… Visual Basic for Applications!!! The school year is starting and things are getting busy so the last thing I want to do is sit down and learn another scripting language. If only, oh if only I could do everything in Python. Well, it turns out I can. It’s a package called DataNitro, and it’s free for personal use.  You can use Python to manipulate data from within an open Excel workbook.  And it’s easy to use.

“How easy is it?” I hear you asking.  Let me show you.  I need a program to go through each worksheet in the workbook, match up the name on the sheet to my master grade list and match up each learning objective to the learning objective on the master list, then copy the score to the master list.  And here is the code:

mainst = 'Sheet1'
for st in all_sheets():
   for nm in range(3,9):
      for i in range(3,9):
         for j in range(3,9):
            if Cell(st,1,3).value== Cell(mainst,nm,1).value and Cell(st,1,2).value == Cell(mainst,nm,2).value and Cell(st,i,1).value == Cell(mainst,1,j).value:
               Cell(mainst,nm,j).value = Cell(st,i,2).value

It took me about 15 minutes to get it working. I’m so delighted. I only wish I had more data in Excel that needed analyzing.

If you want to try anything fancy with Excel, and you know a little Python, I can’t recommend DataNitro highly enough.

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Instructions for starting up with LOBA

With new faculty workshops going on, I’ve had a couple of instructors ask how to get started with Learning Objectives Based Assessment (LOBA) and I thought this would be a good time to summarize how I got started. That was one of the daunting tasks when I started out, and I feel I’ve learned quite a bit this past year.

Writing Your Objectives

Obviously, this is the starting point.  In an ideal world, the best time to start writing is during the term before you start while teaching the class.  All the difficulties and issues students have are fresh in your mind and it is easy to write down a list of objectives you’d like the students to have.  This doesn’t usually work out, so I’d recommend sitting down with your syllabus, a stack of old exams or assignments, and the text.  I chunked everything by chapter, but you can organize the learning objectives whatever way best fits the flow of your class.  As you go through the text, old exams, or assignments, keep a pad of paper next to you and write down important ideas, concepts, or skills that you would have tested for.  For instance, if you are coming from a points-based grading system  and you take points off for students forgetting to include units with numbers, this would be a good skill to write down.  Anything you normally deduct points for, or award points for is a good candidate for a learning objective.

Once you have a list of skills and concepts, start writing out learning objectives.  It is best to write them from the student perspective.  For instance, “I can include appropriate units with all numbers”.  The learning objective should make it very clear what the student needs to do and shouldn’t be vague.  A poor learning objective would be something like “I can write up a good problem solution”.  This doesn’t tell the students what they need to study, or what is important.  The learning objective should make clear what you expect of the student.  With something like writing a problem solution, I would break it up into several small, specific learning objectives like “I can include a free-body diagram with my solution”, “I can list all the known and unknown quantities in a problem”, and “I can check that my answer has correct units and the number I get is reasonable”.

How Many Learning Objectives?

Fewer is always better, both for the students and for your own sanity.  It is way too easy to  write hundreds of learning objectives for a course, but that sets the hurdle too high.  For a 15 week term, 45 learning objectives works out to about 3 learning objectives each week.  The deciding factor in how many is too many comes down to home many learning objectives you can reasonably test in a single assessment.  I have several small learning objectives that can be tested in a single problem, such as the problem solution learning objectives above, so I tend to have more (around 60 or 70 total).

Determine Your Assessment and Reassessment Policy

Placing limitations on student assessment and reassessment is key to students not trying to tackle too much material at once, and to your own sanity.  I typically have two assessments in class each week and only allow reassessment on three days a week.  I should note that having two in-class assessments a week does cost me in terms of how much material I can “cover”, but I prefer a flipped-classroom so I wasn’t assessing I would have students working practice problems normally.  Research has shown that more frequent assessment does lead to better student performance, so I feel the class time “lost” to assessment is a large improvement for students.

The first term I taught I allowed students to specify which learning objectives they wanted to reassess on, but I ended up spending too much time writing up individualized reassessments for each student, which wasn’t feasible.  I know there are instructors out there who do manage to individualize reassessments, but it didn’t work for me.  I let students choose which chapter they want to reassess on, and I have a stack of reassessments ready for each chapter.

I have set up a Google form that students must fill out for reassessment.  The benefit of this is that 1) data from the form is dumped into a Google spreadsheet so each morning I can look up who needs reassessing for each day and 2) I have a ready record of who took which assessment, and when they took it.

Reassessment Request Google Form

It is pretty easy to create a form.  Just go to drive.google.com (assuming you have a Google account, which is free) and click on the “create” button in the upper left side of the screen.  One of the options will be “Forms”.  It is relatively straight forward to create a form, but feel free to email me if you need help.  This form will dump all the data into a spreadsheet on your Google drive.

I require students to make corrections to previous assessments before reassessing, and that they complete a series of homework problems to show me they have practiced the skills.  I also require that students reassess at least once within three weeks of the original in-class assessment.  They are free to continue reassessing as many times as they’d like after that, for as long as they would like, but I don’t want them waiting until the end of the term before they get started reassessing.

Assigning Grades

Most of us need to turn in a final grade at the end of the term so we need to figure out how to go from learning objectives to letter grade.  I have two levels of learning objectives, C-Level learning objectives, which I consider to be easier and more basic, and the A-Level learning objectives, which tend to be more challenging.  To get a C in my class, a student must complete at least 97% of all of the C-Level learning objectives.  If they get 75% of the C-levels, they only get a C-, 65% is a D and 50% or fewer is an F.  To get a grade above a C is determined by how many of the A-levels they have completed.

So how do you complete a learning objective?  For each problem on each assessment, I have a few learning objectives that are tested by the problem.  Each learning objective is given a score from 1 to 4, where 1 indicates a beginning skill level, 2 indicates developing skill, a 3 represents proficiency, and 4 is for advanced performance.  To complete a learning objective, a student must get a proficient or advanced score at least twice on a learning objective.  Ideally I’d like students to show proficiency more often, but I feel that two proficients indicates the student has some knowledge of the appropriate skill.

One thing to note about scoring: a student can get the problem wrong and still get a mark of proficient.  If the learning objective is “I can use F = ma to find the acceleration of a particle” and they have the right idea but make an arithmetic error, I would still give them a proficient mark.  It turns out it is much easier to determine proficiency that to determine how many points you should deduct for a particular error, so proficiency grading tends to be faster than points-based grading.

Keeping Track of Everything

When I first started out, I put boxes with the learning objective number next to each problem, but I found that students would memorize which learning objectives they needed, and that keyed them into how to solve each problem.  To combat this, and to make recording grades easier, I created cover sheets for each assessment like this one:

Example Assessment Grade Sheet

Having all of the learning objective scores on one sheet sped up grade entry, and insured that students couldn’t use the learning objective numbers to figure out how to solve a particular problem; it isn’t enough that a student can solve a problem using energy conservation, I want them to show they know WHEN to use energy conservation.

There are a couple of websites that allow you to track students progress (Blue Harvest or ActiveGrade, for example), and they are fairly good, but they currently don’t support the method I use for determining grades (edit:  Turns out ActiveGrade can do this..Thank you Riley Lark for correcting me).  I don’t average scores together because I don’t want students to think of their assessment scores as points.  I require students get a mark of proficient or higher at least twice to pass a learning objective.  I use a Excel spreadsheet to record individual assessment scores and the spreadsheet figures out how many times a student has passed each learning objective (Email me if you are interested in getting a copy of my spreadsheet code).

Write Your Assessments

If you’ve made it through all of these steps, congratulations, because you are now ready for class to start.  All that you need to do is write your assessments, which doesn’t have to be any different than writing a quiz or exam.  My assessments are really just like a quiz, but I call them assessments to put students in a different mind frame. Students are afraid of doing poorly on a quiz, since it tends to be a one-shot affair, but assessments can be retaken, so there is less stress.  I also like the term assessment because it can take other forms, such as oral presentations, webcasts, or simply answering a few questions in my office.  I’m not constrained by the traditional format of quizzes and exams.

I currently only have three or four versions of each assessment, with problems from widely varying contexts.  I keep track in my Google spreadsheet which version I gave each student so when they come in to reassess I don’t give them the same version.  I don’t doubt that some students might get copies of previous reassessments from other students, but I haven’t seen and evidence of it and for the most part I don’t think only having a few versions is a problem.  Each term I plan on adding another version or two, so that in short order I’ll have enough reassessments that I won’t need to worry about student’s sharing answers.

Sell It To The Students

Your students have spent at least a decade mastering how to get the most points with the least amount of effort and they will be very nervous with such a radically different grading paradigm.  You will need to explain to your students why you are doing this, spend time reassuring them that being able to reassess means less stress on them, and the learning objectives make it very clear exactly what they need to do.

You will also need to explain the grading on several different occasions over the first several weeks.  Even after three weeks, some of the students had questions about how things worked so I gladly set aside time to explain things to them.  Once they got the hang of it, though, many of them liked it.

Three Final Thoughts

The first time I taught using LOBA, I handed out a compete list of all learning objectives at the beginning of the term.  Unfortunately I found some objectives too easy, some too hard, and some just a waste of time and I changed some of them mid-term.  Big mistake.  The students felt I was moving the bar and were very stressed out by this.  If I had to start over again, I think I would only hand out a list of learning objectives for the next chapter or unit as we covered the material, which would allow me to change later learning objectives on the fly.  This also means you don’t have to have all of your objectives nailed down before the term starts, which can take some of the stress off of you.

I have found that my grade distribution is skewed towards higher grades.  I first thought that I wasn’t setting the bar high enough for A’s, but I realized that since students know what they need to do to get an A, they can push themselves.  I had one student who figured they were getting a B+ and where happy with that, but when they realized they only needed a few more learning objectives to reach the A- mark, they pushed to get it.  If a student knows exactly what they need to do to get a better grade, they will.

Lastly, I highly recommend checking out blog posts on the web.  I have a number of other posts on LOBA (or Standards Based Grading (SBG) as it is sometimes called) and there are a number of great resources.  I’d recommend Frank Noschese’s blog, Action-Reaction, John Burk’s Quantum Progress, and any of the SBG Gala’s (Gala #6 is here and has a list to earlier galas).  Check out these great resources.  Best of luck.  You are going to love it!

Addition:

A few people have asked for the Excel gradebook file so I thought I’d post it here: Gradebook – LOBA

Instructions:  On the “Totals” tab, enter the student names in the first two columns.  Copy and paste that list of names to the second tab labeled “Assessments”.  The order of the names matters because row 2 on the “Totals” tab is connected to row 4 on the “Assessment” tab.  Columns C and D on the “Totals” tab tells you how many A-level and C-level learning objectives each student has completed (scored 3 or 4 on that LO at least twice).  The top row of this tab is for the name or number of each learning objective.  On the “Assessments” tab, you can enter the scores for each student on each learning objective.  I hope this is helpful to some of you.

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Mystery Streak During Venus Transit

My colleague, Alan Scott, went out with a telescope yesterday to view the transit of Venus across the Sun. He caught a mysterious streak which appears to be passing near the Sun.  This is an awesome (and serendipitous) video.  Great job Alan!

Posted in Just for Fun | 1 Comment

What I Learned At Faculty College

I just got back from a wonderful week of talking with other educators. Every year the University of Wisconsin System Office of Professional and Instructional Development (OPID) holds a four day faculty college where instructors from the UW system can get together and talk teaching. The program is part of the Wisconsin Teaching Scholars program, and is aimed at promoting the scholarship of teaching and learning (SoTL).

Those of you not in academia may wonder what SoTL is, and it just so happens we spent quite a bit of time trying to come up with a definition.  It basically boils down to researching how best to teach your own students.  I like to think of it as getting to experiment on my students with the added benefit of getting a publication at the end.  The primary goal of SoTL is to advance the practice of teaching.  In other words, we find out what sort of things help students learn better.

So, what did I learn?  First, designing a SoTL project is hard, but the hardest part is, surprisingly, limiting the scope of your project.  Several of the faculty I talked to (including myself) had projects which would probably fill up a couple of PhD dissertations.  So the steps to coming up with your project is one of whittling down, and narrowing your focus, until you have something that is realistic and manageable.

The second thing I learned about what Perry’s model of intellectual development.  I try to relay my own (very) limited understanding of Perry’s model.  Students come to college with a simple, dualistic view of the world.  The dualist see things in terms of black-or-white, right-or-wrong, and believes that most problems can be solved by simplying following the word of the Authority.  The next stage is the multiplistic view,  students begin to see that there is no Authority, that there is significant uncertainty in all fields, and that other opinions have validity.  Unfortunately, students in this stage tend to believe that all opinions are equally valid, and aren’t able to understand that some opinions might be better than others.  Hopefully these students can advance to the next stage, which is relativism.  This is the belief that context matters, and that some opinions are better is some circumstances and that by using evidence, you can often choose a better choice from an array of options.  Only some students will make it to this stage, but most don’t make it to the next stage while in school.  The final stage is commitment in relativism.  In this stage, the student takes a stand and makes a commitment based on a logical evaluation of evidence.  In other words they can decide what appears to be true.

The reason this model struck me was I realized many of my students are still in the dualistic stage.  They see me as the Authority, and do not like trying to work things out on their own.  The feel that “teaching” means that I should be telling them what they need to know.  I think I was heartened to realize that this was part of a natural progression, and that these students might not be stuck in this black-or-white world.

Can you tell most of my writing lately has been academic papers?  This post feels very passive-voiced.  Oh well.  If my explanation above seems a bit muddled, it’s because I’m figuring things out for myself.  Incidently, “muddling” and “strategic confusion” where the key phrases for the week.  Any of you readers that are Wisconsin faculty, I strongly encourage you to attend Faculty College.

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