EEVblog #622 - How To See-through Objects With A Thermal Camera

[EEVblog]

Dave shows you a handy tip on how to see through your product using a thermal imaging camera with the cover *on*. Thus being able to maintain the correct airflow, whilst at the same time being able to view the thermal map as if the cover was off!

[Taucher]

Nice vid

I've read the E8 has an upgrade by Flir (grin) available to include manual (fixed) temperature range - that might have been handy to stop the camera's auto-ranging to just follow the temp-profile.
If you want a "Just Dave it" edition then just drop us a note *G*

Btw - used my thermal cam in fixed mode while performing hot air re-soldering of a a BGA - was quite helpful not to burn surrounding stuff - and one doesn't have to use the spot measurement feature to see the real temp

[NiHaoMike]

Any concerns with ESD?

[EEVblog]

Any concerns with ESD?

Meh.
You generally wouldn't wrap the PCB in the stuff.

[Taucher]

Any concerns with ESD?

Meh.
You generally wouldn't wrap the PCB in the stuff.

This reminds me that I was wanting to investigate further details about that nice little ESD measurement device that I've seen some times in your blog ... but never a teardown of it
(seen it in ep #247 - ) - AlphaLab Surface DC Voltmeter KV@1

Found two quite interesting texts regarding such devices:
http://www.qsl.net/k/k0ff/7Manuals/Static%20Electricity/The%20Surface%20DC%20Voltmeter%20and%20its%20included%20accessories%20make%20a%20complete%20%93kit%94,%20used%20to%20measure%20all%20the%20forms%20of%20static%20electrici.htm

https://e-reports-ext.llnl.gov/pdf/374701.pdf

[TVman]

Nice video Dave!

[Odysseus]

That's some out of the box thinking!

I wonder how much heat escapes via infrared radiation through the transparent cling wrap that normally would be absorbed or reflected with an opaque case.  My hunch is that it's quite small compared to convection/conduction. Off to Wikipedia...

EDIT

Here we go: http://en.wikipedia.org/wiki/Stefan-Boltzmann_law , http://www.irf.com/technical-info/appnotes/an-1057.pdf

If my calculations are correct, an object of unity emissivity at 70C will radiate ~30mW per cm^2 of surface area in a room temperature environment.  Pretty insignificant.

[Taucher]

That's some out of the box thinking!

I wonder how much heat escapes via infrared radiation through the transparent cling wrap that normally would be absorbed or reflected with an opaque case.  My hunch is that it's quite small compared to convection/conduction. Off to Wikipedia...

That's not so far off - AFAK some 2/3 of the overall thermal transport is done by photons - but as it's in an equilibrium with the surrounding that effect is usually neglectable for ventillation tests - I'd say if the construction overheats with the cover but does not with the wrapping, then that design is way too close to a critical point anyway.

[EEVblog]

I'd say if the construction overheats with the cover but does not with the wrapping, then that design is way too close to a critical point anyway.

That would be my thinking too.
In any case the effects of forced air flow would dominate, and the cling wrap keeps the air flowing where it's supposed to.

[DJ]

Neat vid.

I would be a little cautious regarding static charge. Back in the 80's I had a static charge meter, which was possibly more critical - fet's tended to be more delicate, and we'd see increased fallout during the drier winter months. I seem to recall peeling off a bit of scotch tape as easily generating 5 or more kv. Cling wrap I would expect could be in that neighborhood.

Most devices are of course more secure once in-circuit, but most esd testing is designed for assembled product.

Tearing a sheet of plastic off, then laying it on metal to drain off any charge would mitigate risk, I'd think.

[SeanB]

Cling film is easy to handle static wise if you are prepared to lose the cling ability. Simply take an old household spray bottle ( the common use once ones you get cleaners in are fine) and rinse it out, then add a tablespoon of liquid fabric softener and fill with water and shake well to mix. Pull the cling film off away from the bench, and place on a flat surface and tape it down, then spray lightly with the softener, wipe dry, turn over and tape down again and repeat for the other side. You lose the ability for it to cling, as that is a function of surface static charge, so you will have to tape it down.

[EEVblog]

Bit of a cheeky title. 
It'll be interesting to see the YT view stats. I'll bet the same crowd that got excited about the camcorder IR seethrough clothing nonsense will turn up.

You gotta be an SEO whore in this business 
Seems the video is already number 3 on youtube for the generic search term "thermal camera" ?

[miguelvp]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

[Taucher]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

The far-IR transmission of a material depends on its bandgaps - LDPE is quite transparent in thin layers

Much more fun: inspect a chip-wafer (germanium or silicon) - depending on the N/P/bare type you'll be able to see through in IR... or not

[miguelvp]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

The far-IR transmission of a material depends on its bandgaps - LDPE is quite transparent in thin layers

Much more fun: inspect a chip-wafer (germanium or silicon) - depending on the N/P/bare type you'll be able to see through in IR... or not

Even red wine or coca cola will be transparent on IR and will look like water.

The problem with the anti-static bags or the film is that it will block visible light, but then again, if you only care about the thermal image then it doesn't matter.

[Legit-Design]

Bit of a cheeky title. 
It'll be interesting to see the YT view stats. I'll bet the same crowd that got excited about the camcorder IR seethrough clothing nonsense will turn up.

I think one camcorder IR seethrough had boobs in it. Maybe that was the reason.
https://www.youtube.com/results?search_query=see+through+clothes

this one with 37,934,405 views

[speedyant]

Try those for microwave oven.




Yes, i have used google translator... 

[SeanB]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

the large ones I use at work are quite reflective in IR, as they are designed to both reduce static and reflect heat away to control the inner side temperature. Big enough to use when camping as a sleeping bag outer liner, 10 minutes under one and you are cooking.

[cyr]

Even red wine or coca cola will be transparent on IR and will look like water.

The problem with the anti-static bags or the film is that it will block visible light, but then again, if you only care about the thermal image then it doesn't matter.

I think you must be thinking of other IR wavelengths. Water is basically opaque as far as my thermal camera is concerned, and I'm sure that will apply to any beverage (and of course the glass you are likely to keep it in).

My anti-static bags are also very thermally reflective, not transparent at all.

[tinytim]

as a side thought, i wonder if Dave would put the Flir in front of the Atten 858 so we can see the airflow and adjust the flowrate and temp.
I am interested in knowing if there is any advantage in using just enough temp and low airflow as opposed to high temp, a larger distance and flowrate. I assume that by using just the minimum temp and min airflow required would substitute "perfect" conditions for reflow.
Also i wonder how good the calibrated temp control is, just where is the temp point measured from, the nozzle? from a distance?

Your thoughts?
Tim

[EEVblog]

as a side thought, i wonder if Dave would put the Flir in front of the Atten 858 so we can see the airflow and adjust the flowrate and temp.

I thought about this. The max temp range on the E8 is only 250C, but still should be fine for seeing a board/part come up to temp.

[tinytim]

as a side thought, i wonder if Dave would put the Flir in front of the Atten 858 so we can see the airflow and adjust the flowrate and temp.

I thought about this. The max temp range on the E8 is only 250C, but still should be fine for seeing a board/part come up to temp.

I wonder how effective Kapton tape is since i use it primarily as a masking for adjacent smd devices, would be great to see some airflow maps so we can see what goes on either side of the tape - so many questions on what seems to be a largely ignored / dismissed subject.  Thanks for the vids Dave. Awesome.

[max_torque]

The interesting point is that this video demonstrates the benefits of a "precision" cooling design.  The Filter instrument doesn't really has a precision cooling design.  So, lid on or lid off, the bulk of the cooling is driven by local convection.
 
Yes, the fan removes that heated hot air from inside the box when the lid is on, but the mean velocity over the individual heat sinks (even those close to the fan) is too low to significantly boost the performance (degC/W) of those sinks via forced convection.  (This is because forced convection really only starts to occur when local flow in the heat sinks boundary layer becomes turbulent. i,e, that largely static boundary air is broken down by high velocity air moving and swirling around it).

  So in that case, the heat sink temps don't change too much between having the lid on or off (when the lid if off, the lower density hot air natually rises away, pulling cold air into it's place).
In the case of the filter instrument, the fan really is there to ensure the bulk temperature inside the device stays within a few degrees of ambient, NOT to ensure any particular component of sink is cooled!  (This is important for instruments that may be mounted in racks (where they get upheat from their neighbours) and/or used in higher ambient temperatures etc)

For the 'scope, the individual ICs that are rejecting heat don't have a good sink (high thermal impedance), so they require the fan to be blowing high velocity air.  This is getting closer to a precision cooling design, where you need to have the covers on (or cling film instead) to ensure the air paths impinge on the correct location.  Without that turbulent air flowing over the specific ICs the device overheats.

We of course see proper precision cooling in devices like DC loads, Power supplies or modern PC's laptops etc, where specific and direct airflow is used to ensure sufficient heat is removed directly from the device being cooled, and not just allowed to spread into the general internals of the device.  In those cases, fans directly on heat sinks, or moulded channelling etc (or even heat pipes etc) are used.


It's also worth noting that with IR measurement "emissivity" is everything.  Generally, the camera will be set for a fixed value (usually a "black body" value.  So, for accurate measurements you either need to correct the camera settings for the objects you are pointing it at, or another common option is to just lightly spray the entire pcb with black spray paint!!

[Taucher]

as a side thought, i wonder if Dave would put the Flir in front of the Atten 858 so we can see the airflow and adjust the flowrate and temp.

I thought about this. The max temp range on the E8 is only 250C, but still should be fine for seeing a board/part come up to temp.

the "calibrated" scale goes to 250 ... the camera will actually show temperatures up to 280°C and then just ">280°C"

@Airflow - due to a lack of mass the airflow is never visible - only its effects.
I've attached a couple of images taken with my Flir E4+
... the solder iron tip had 350°C temperature (ERSA iCon iTool)
two images show my hot air station in action - please note that some components around the BGA chip seem to be really hot and others seem to be very cold - both is due to metallic (mirror) reflection and should not be confused with the medium-hot reality

The last image shows a simple PCB under load - one can see how the chip-die is much smaller than the outside package.
Note the temp-scale when comparing images!

[zapta]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

Or even better, run the unit with the stock cover, open it and take a quick snapshot with the FLIR.  Then you have all the time in the world to analyze it with the FLIR software. Air flow and heat dissipation will be more realistic.

[Taucher]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

Or even better, run the unit with the stock cover, open it and take a quick snapshot with the FLIR.  Then you have all the time in the world to analyze it with the FLIR software. Air flow and heat dissipation will be more realistic.

That would need to be done really quick as thermal equilibrium is astonishingly fast-changing and the extra air-movement would cool in addition - but I guess it could be solved with the PE wrapping below the case to be taken off (perfectionist solution) *G*

[Fraser]

For info, FLIR produce 'cheaper' disposable lens protectors that use Polyolefin heat shrink plastic as the window. FLIR don't advertise the material used as they still charge serious money for these lens protectors ! I detailed the material in my E4 Useful information thread in November 2013:

https://www.eevblog.com/forum/reviews/flir-e4-the-useful-information-thread/msg332125/#msg332125

The Polyolefin plastic is chosen because of its excellent transmision characteristics, and the good news is that it is easily available cheaply as detailed in my posting.
 
The material is more controllable and robust than thinner 'cling' type plastic films and may be stretched over a frame and shrunk tight with a hair dryer.

If working with equipment that could suffer catastrophic capacitor failure it would also be a good idea to protect the camera face/lens from flying fluids with such material.

Aurora

[nitro2k01]

The followup video is up!

[zapta]

Dave, can you compensate for the reduced temperature reading through the plastic wrap by changing the emission setting of the FLIR?

[Taucher]

Dave, can you compensate for the reduced temperature reading through the plastic wrap by changing the emission setting of the FLIR?

technically it is possible to change the emissivity setting inside the camera to adjust for errors.

[speedyant]

I know the temperature of the "thing" is 20 degree, try all the "clean wrap" and see what happen, make a kind of calibration.

[Taucher]

I know the temperature of the "thing" is 20 degree, try all the "clean wrap" and see what happen, make a kind of calibration.

actually the real method should be very similar:
- take reference measurement at thermally stable surface/object body with thermocouple
- measure the value with the thermal camera
- calculate correction-factor
- change correction factor in camera according to match the real world - keep in mind the already set up factor in camera
- iterate or fiddle around with value in case it does not match until happy with result
- re-verify that both measurements are equal (crosscheck both in case of deviations over time)

[miguelvp]

So, what happens if you blow hot air on the antistatic bag, will it show airflow?
Seems to retain the heat long enough for that.

[Fraser]

For those interested in IR transparent materials there is plenty of information on the NET detailing how different materials behave at the various wavelengths used in thermal imaging. I attach a simple table of materials that may be used in lenses and a link to another version that clearly shows the three different wavelengths used in the industry, Short, Medium and Long wave. The E4 is a long Wave thermal camera. Some material, such as silicon are not well suited to Long wave lens structures yet work fine at shortwave 

http://www.infraredtraininginstitute.com/infrared-transparent-materials/

There are similar tables for thin plastic but I have not tracked them down yet. I will add them if/when I do.

Dave's experiments have been good at demonstrating how materials behave in these areas of the EM spectrum.

Something that is also worthy of experimentation is emissivity. This can have a really dramatic effect on any temperature readings. As an example, a nice shiny aluminium heat sink can be running at +80 Degrees Celcius yet the thermal camera can misread it due to emissivity error and show it at ambient ! The emissivity setting in the camera should be set to the value of the target item to achieve the most accurate measurement. Life is never that simple though....how do you know the true emissivity of a target surface ? That's a whole other story that I will not go into here. Some people may think that to solve the emissivity problem, just paint the target matt black..... well they are on the right path but readers should be aware that where paint in concerned, colour often makes no difference at thermal wavelengths in terms of emissivity. Silver paint and paint loaded with metals may behave differently (worse) to a nice matt paint but basically you will still not have a perfect emissivity in either case. To achieve 'Black body' levels of emissivity (1.00) a very special paint coating is needed that radiates the heat far more efficiently than any generic paint. It may also be interesting to know that the soot from a candle is a very good coating where good emissivity is required. Also a common material used as a quick and dirty emissivity enhancer is everyday standard PVC insulation tape. Colour is NOT critical  A shiny metal surface with low emissivity may be easily measured with a TIC once a piece of PVC insulation tape is applied. From memory the emissivity of PVC insulation tape is 0.96 to 0.97.

Readers should also be aware of the issues created by reflections. If a thermal camera is brought into close proximity of an object that has reflective thermal properties, it is possible to actually skew the measurements as the camera actually starts to see itself reflected in the target and the E4 has a core running at around +30 degrees C that emits through the lens and may be reflected back at the camera. To see an extreme case of this, point the E4 at a mirror or glass and you will see a selfie  The lens will look warmer than the case....you are seeing the reflected core temperature.
Cryo-cooled cameras project a cold image from the 70K core through the lens that has the opposite effect on readings. These effects are most apparent when working in a close-up configuration with variable target materials. There are plenty of traps for the newbie thermographer 

All this is drifting off topic I know, but I just wanted to highlight that there are some very interesting experiments that may be carried out using a thermal camera. Hours of fun on a wet day if you are bored 

Oh and nit picker time..... the Ex series cameras do not use a Germanium lens as stated in the videos. Chalcogenide glass is the material used in these and many other 'budget' thermal cameras as it is far cheaper than Germanium in terms of production costs. Germanium crystals are cut to shape with a single diamond tool, Chalcogenide glass may be moulded.

http://www.lightpath.com/infrared-optics/thermal-imaging-assemblies.html

[EEVblog]

Dave, can you compensate for the reduced temperature reading through the plastic wrap by changing the emission setting of the FLIR?

Yes, there is a setting for emissivity if you want to experiment and find the correct value for a particular surface.

[babysitter]

I have a nice benchtop experiment that I showed our trainee to tell him about transparency and opacity outside the visible range - namely IR.

A GaAs Wafer in its plastic holder we got as a present, he had to irradiate it with a TV remote control from one side and look at the other side with his smartphone camera. Could have told him to look at the case of reflection too..Actually, different LEDs and heating/cooling might show the effect of its temperature-dependent optical properties of GaAs...

A Thermal imager is a instrument like any other, one needs to understand it to use it.

[Fraser]

More trivia

I have experimented with GaAs lenses and windows at Long Wave and they do perform OK. What is interesting though is the issue of anti-reflective coatings. Many materials including Germanium (yes Germanium) have poor transmission figures due to reflection off of the first surface interface. Special anti-reflective coatings are needed to achieve acceptable performance. This is why it is VERY important to treat a thermal camera lens with great care. Removing the anti-reflective coating can destroy lens performance and so ruin a cameras calibration. Anti-Reflective coatings can also be wavelength specific so a lens designed for Short Wave use may perform very poorly at Long Wave and so will be unsuitable fro use with the E4.

Aurora

[Wim_L]

Indeed. The reflection is caused by the very large refractive index difference at the interface between air and the lens. Optical glass has a fairly modest refractive index contrast, its refractive index is around 1.5 (versus about 1 for air or vacuum). Semiconductor lenses have a pretty high refractive index in the infrared, about 3 to 5. This can be beneficial sometimes (it allows for making lenses with a short focal length with less curvature than would be needed in a glass lens, so thinner and lighter lenses are possible), but does create enormous reflection losses if the lens isn't coated properly for the wavelengths it's used for.

[DJ]

Just watched Dave's update video, clears up all our questions nicely

As for lenses, the single element mods are nice for closeups,  wondering about options for telephoto - something along these lines but less expensive



http://www.nightoptics.com/no/product/TO-3X-AF.htm


eta: that 3x lens is ~$950usd on Amazon.com

[Fraser]

@DJ

Sadly the construction of a telescope for the E4 requires lenses that are not available cheaply. The close-up lenses are easy as CO2 lasers use them in cutting applications. For a telescope a larger lens diameter would likely be needed and longer focal lengths. I have found neither at reasonable cost.

I ended up buying used telescopes when the price was right (rare these days) I paid $150 each for my X3 Inframetrics telescopes and $400 for a superb quality FLIR X2 compound telescope. That was the only way I could find of getting a telescope with decent performance. If anyone knows where larger diameter and focal length lenses are available at reasonable cost, I would love to know. The X2 FLIR telescope uses only 2 Meniscus lenses but they need to have the right focal length for the application and Germanium is used due to its higher refractive index (greater bending of the EM beam) producing a compact design. A chunk of Germanium lens like that use in the FLIR telescope costs serious money 

I will take a quick picture of the Telescopes cross sectional diagram (supplied by FLIR) in case it is of interest.

I have also considered the construction of a reflector telescope but finding a surface mirrored concave mirror for the task has proved challenging.

Aurora

Update:

I have attached the cross sectional views of the FLIR PM series X0.5 and X2 auxiliary lenses. My Inframetics X3 telescopes contain four lens elements but are inverting and may not actually need all four lenses in our application (still under investigation)

[Zucca]

On the side... Thanks Dave to give me the idea on how to improve the calibration procedure on my Keithley 220:



Those unit needs to be on at least for one hour to get to the proper work temperature, only then you should start to calibrate by tuning the pots on the boards. The problem is to reach those ones you have to remove the cover... and bye bye heat.

[DJ]

I would think that some small access holes in the wrap would retain most of the heat whilst permitting access to the pots. Is the factory case solid (ventless)? A temporary IR wrap should mimic the original enclosure physically.  Note also a metal enclosure will sink and reradiate heat. Suppose one might look at the k-factor of thin plastic films vs whatever the original material was.

[Zucca]

I would think that some small access holes in the wrap would retain most of the heat whilst permitting access to the pots. Is the factory case solid (ventless)?

Yes you got it, little holes for the Wiha screw driver. The factory case is solid with no metal, just a piece of solid plastic.

[MindBender]

Cling wrap: Bloody brilliant Dave! As a software engineer, I'm not really involved in thermal design, but I have been using a Flir A40 camera for years during board bring-up, allowing me to cut the power before a precious prototype burns up at first power up.

However, if you want to see the airflow through your product to verify the thermal design, use your cling wrap setup as you did and spray a whiff of freeze spray at the fan inlet. Depending on how big of a whiff you're spraying, you should be able to see a black cloud traveling through the device.

[Crossphased]

I was just watching this video, and was wondering-

Why aren't Dave's hand and arm showing up as hot in the thermal pictures? His hand shows up as cool blue, when it should be hotter than the ~75 degree IC that was being measured. What was happening?

[IanB]

Why aren't Dave's hand and arm showing up as hot in the thermal pictures? His hand shows up as cool blue, when it should be hotter than the ~75 degree IC that was being measured. What was happening?

Degrees Celsius (shown as °C on the display).

If Dave's arm was hotter than 75°C he would be dead. The actual temperature is somewhere between 30 and 35°C.

[Brumby]

75ºC is 167ºF

Just sayin.....