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Appaulingly t1_j5ojqgw wrote

Thermal cameras aren't that great at accurately measuring temperature particularly when comparing different materials. The emissivity of the metal with be very different to that of the other materials and so a different temperature will be measured.

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dumb_password_loser t1_j5opqcs wrote

Yes, he just sees a colder environment (assuming door is open) reflected on the metal.

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Detectorbloke t1_j5oq3uv wrote

In addition: There's special paint to measure the temperature of normally reflective surfaces.

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AbnormalMapStudio t1_j5pl9jf wrote

Even easier, you can buy emissivity labels (also called IR labels) and just slap a sticker on.

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dr_reverend t1_j5rb0ol wrote

Even easier. Just use some masking tape.

Recommended up to 100c but I doubt 105c would be a problem.

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Lampshader t1_j5rzle5 wrote

The FLIR sales rep recommended black electrical tape when I asked about this.

I dunno what its melting point is but 98% of electronics workbenches will have it within arm's reach already so it's got that going for it

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bella_68 t1_j5s8tpz wrote

Idk how hot a car gets when sitting in the sun but it was hot enough to melt the glue on the electrical tape covering my steering wheel. Interestingly, the glue was liquid and the liquid was everywhere but the tape was still on the steering wheel because the way it was wrapped and the fact that the glue was also still there to some extent.

Unfortunately for me, I get a rash anytime I touch glue

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ArchitectOfFate t1_j5u5knj wrote

The tape itself has NEC standards regarding when it melts and burns, and is designed primarily to melt unless exposed to really extreme temperatures. There’s usually a rubberized or vinyl part of the tape that can turn it into a sticky mess. Good electrical tape shouldn’t have problems at “normal” temps, but on a hot day in the south/southwest a car can get upwards of 150 degrees F, which is pushing it even for the good stuff.

Humidity also doesn’t help and can cause some glues to break down faster.

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VoilaVoilaWashington t1_j5vaa02 wrote

> The tape itself has NEC standards

Which is probably not true of random black tape people buy at the dollar store.

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ArchitectOfFate t1_j5vfsry wrote

Exactly. I didn’t want to accuse OP of buying cheap tape, but proper electrical tape will be clearly labeled as electrical or electrician’s tape, will have the NEC standard on it, and costs $3-$5 a roll unless you’re buying in bulk.

And even then the minimum is 170 degrees. 3M and a couple other companies certify their vinyl tapes above that, but one that’s barely compliant could still get hot enough in a hot car for the glue to start to soften.

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BeetsMe666 t1_j5ug11a wrote

I am a refrigeration mechanic and have had to inform far too many restaurant operators about this fact.

They log the temps in the equipment taken by an ir gun, and they are all over the map. The most consistent recording is done with a probe thermometer in a bottle of water.

Too many employees don't question the reading and just log the number that is far out of range.

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SXTY82 t1_j5p8cb0 wrote

The first time I took a look at a window with my thermal camera I could see the reflection of myself in the thermal image but not in the window itself.

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ThisTooWillEnd t1_j5ppwaq wrote

I've been playing with a thermal camera and not only do I observe what you're describing, I also clearly saw my reflection in a tile wall with the thermal camera.

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Dusty923 t1_j5pj1j7 wrote

Glass reflects different wavelengths of light differently. House windows may also have an infrared-reflective composition or coating (for more efficient cooling in warm sunny weather).

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Denamic t1_j5rocnx wrote

Thermal cameras use IR. IR, being light, bounces off reflective surfaces.

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zebediah49 t1_j5s0zx3 wrote

The relevant point is that visible light will happily go through a normal glass window, whereas long-IR will not. Windows are opaque (and pretty reflective) to thermal cameras.

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SXTY82 t1_j5p84u4 wrote

yes. Also the reflectivity will affect non-touch thermal measurements. I use them at work now and then and anything that is silver colored, even non-shiny metals, I have to paint black to get an accurate reading from them.

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VulfSki t1_j5r0tb4 wrote

This is the answer.

I have used thermal cameras in my line of work work a part in an oven.

And I have literally been able to see the reflection of my own body when I pointed the thermal camera at the metal walls. That's likely the issue here. An emissivity issue.

The coworker's explanation sounds like a misunderstanding of how convection works. Just because air is flowing, doesn't mean it's cooling down the metal. Flow doesn't equal cooler. You need to remove the thermal energy somehow. If it's a closed system the heat isn't going anywhere.

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chillaxinbball t1_j5rd007 wrote

The best way to think about thermal cameras is to think about cameras.

Imagine you are trying to measure how hot something is by how much it's glowing. For example you go to resistive coils and see how bright they get. You can get a decent measurement just by seeing how bright it gets. Now try to measure a mirror reflecting an image of the coils. You'll get a very similar measurement. Is this because the mirror is just as hot? No, you are mostly measuring the reflected image of the coils and not the mirror itself.

It's the same thing with thermal cameras. Metal is very reflective at the wavelengths used to measure thermal radiation. You are essentially looking at a mirror and will not get accurate readings from it in much the same way.

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Glasnerven t1_j5rhfa4 wrote

> Just because air is flowing, doesn't mean it's cooling down the metal. Flow doesn't equal cooler.

Roughly speaking, flow equals better heat transfer. We're used to thinking that flowing air = cooler because we--our bodies--are usually warmer than the air around us. Even if it's hot enough outside that the air is warmer than we are, then we're probably sweating, so we have evaporative cooling going on--and flowing air makes that happen faster.

So, in our personal experiences, we almost always find that it feels cooler when air flows over us. It's really easy to over-generalize that and assume that it's a universal law.

You can easily test it at home, though. Get two little cups of ice, make sure there's the same amount of ice in each one, and then put a fan on one and let the other sit in still air. You should notice that the ice with the fan melts faster--the flowing air is heating it faster than the still air is heating the other ice.

You might also already have a device built around this effect: a convection oven or air fryer.

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VulfSki t1_j5rqk0a wrote

Yes, I understand how all that functions. Humans get cooked down from perspiration, which is because the energy to evaporate sweat is partially comes form the heat on our body, and air flow helps with that.

But airflow itself doesn't equal cooking in the general sense, because it only works if you are removing heat by taking it to something that is at a lower temperature, can't violate newton's law of cooling.

You did provide a great explanation, even though I was already aware of all that.

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orange-cake t1_j5pkl19 wrote

I've seen laser thermometers that can measure emissivity, are they able to accurately compensate or do you need to know the material?

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MasterPatricko t1_j5pzgt2 wrote

A "laser thermometer" as commonly sold is just a small FoV infrared thermometer with a laser pointer strapped on top. (The exception is very advanced thermometers which use calibrated lasers and optical ranging to measure reflectivity.)

Usually these thermometers accept emissivity as a setting. They don't measure it.

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InfintySquared t1_j5q3tvm wrote

> Usually these thermometers accept emissivity as a setting

That little nugget said more than most of the in-depth answers above. Thank you, you done good.

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