What is the difference (if any) of a thermal versus infrared camera?

[Ron247]

I am trying to find out if there is any substantial difference in a thermal imaging camera versus an IR camera. Some sources appear to use the terms interchangeably and other sources act like there is a difference.

I am mostly looking for a helpful tool in detecting moisture in buildings.

 

[EdStainless]

The way that the terms are used generally they are the same thing.
If you are going to use one then you should learn some of the operating theory.
Their conversion of reading to temp is very approximate with any surface or temp different from the calibrated one. They can give you good relative data, surfaces that they say are different temps usually are. Just don't get to wrapped up in the numbers.

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[3DDave]

Typically "thermal" cameras operate near the 10,000 nM wave length and can detect photons that can be from room temperature and up. They typically use Germanium lenses which are opaque to visible (700 - 400 nM wave lengths) light.

IR cameras typically refer to those sensitive in the 800 to 1000 nM wave length, which is emitted from source well above room temperature or from suitable electron transitions such as in light emitting diodes.

Most digital cameras use silicon based sensors which are sensitive to IR use an IR filter to exclude unwanted exposure.

Aside from temperature range, the practical effect is that thermal cameras can operate in the absence of typical light sources while IR cameras depend on some illumination source - often IR emitting LEDs.

In the old days, IR black and white and color film for cameras was produced - obviously, if they would be exposed by being warm they would be useless.

 

[IRstuff]

Leave to civilians to be sloppy about terminology; ANYTHING over 780 nm is technically infrared:
> 800-1000 near infrared (NIR)
> 1000-2500 short wavelength infrared (SWIR)
> 3000-5000 medium wavelength infrared (MWIR)
> 7800-14000 long wavelength infrared (LWIR)

Cameras in the latter two bands are also considered thermal cameras seeing objects' self-emissions, since the former two bands are not readily emitted by objects, and what those cameras see are reflected light. So caveat emptor; lots of people simply call their cameras "infrared" knowing that newbies will think they're thermal cameras and buy them because the price is so cheap. High performance thermal cameras are expensive, because the detectors and optics are exotic materials and the detectors need to be cryogenically cooled. InGaAs detectors that cover 900-1700 nm are also expensive, because the material is relatively exotic and yields are low. There are cheap(er) uncooled bolometric thermal cameras, but their sensitivities are adequate only if they're matched with low f/number optics.

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[EdStainless]

For example following IR's comments, my Sony video camera that has 'low light' mode. When it is off it filters out everything beyond 800nm, when it is turned on it adds the NIR and most of SWIR to the image.
If you add visible light filers and turn it on you can look at items in daylight and see 'hot spots' but it can't be used to quantify (too little energy in those bands).
The resolution and detection ability of a device are a function of the optics and sensor.
If you are just looking for hot or cold spots relative to a background then you don't need much. Many of the simple ones that overlay a low resolution NIR image over a real image are fine. If you want actual temperatures then you need a lot more device.


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[Ron247]

Thanks everyone for the info. Based on the responses, if I want something to help detect potential moisture problems in walls and ceilings I need to buy at least a MWIR or LWIR as noted by IRstuff. I basically need to pony up the $$$.

I have had a FLIR camera that attaches to my Iphone but have only used it to find wall/ceiling framing. I have never used it to estimate moisture. Being a structural engineer, it is very helpful finding which direction a ceiling is framed, unusual framing and other items. Recently I was doing some structural review following hurricanes and high winds. I ran across numerous owners that said someone in the moisture removal business came in with a IR or thermal camera (they don't know which one) that scanned their house and instantly said the wood framing was 30% moisture and needed drying out. The person never took any actual moisture reading with any moisture equipment. Is that even possible?

I realize the scanners are taking temperature measurements which have no direct relationship to moisture as I see it. I do realize a scanner can be used to help find "relative" differences such as "this is possibly wetter than that" but not an actual moisture content.

Can you guys give me some guidance on this?

 

[3DDave]

Moisture will increase the thermal conductivity so one could see higher temperature gradients as a result. It's not detecting moisture, it is detecting the temperature distribution that results from the moisture. The result may be higher or lower temperature depending on the exact situation.

I expect with experience a user following up with a moisture probe that a person might get enough background to skip the measurement step or they could be just making an estimate of unfounded precision. It's easy enough to double check a few places.

The better question is if they are close enough to the truth about moisture accumulation sufficient to support mildew and rot.

 

[Ron247]

3DDave-That is what I felt a person might be able to do with time. Basically, they could gather a database of conditions that yielded some "color" that was later correlated to an actual moisture measurement.

The database info would be elaborate but not completely ridiculous.
[ul]
[li]Outdoor temp[/li]
[li]Indoor temp[/li]
[li]Ext wall covering (brick, wood, etc.[/li]
[li]Int wall covering (1/2" drywall, 1/8" paneling etc.)[/li]
[li]insulation sheathing type and thickness[/li]
[li]wall insulation[/li]
[li]what color/shade correlated to a wood moisture content[/li]
[/ul]

 

[EdStainless]

May hunch is that the guy tells you a moisture content based on the combination of experience and his need for current work.

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P.E. Metallurgy, consulting work welcomed

 

[3DDave]

The displayed "color" is related to the temperature and emissivity and settings that scale the output of the sensor to the display and those will change; it won't be a constant. If it is cold outside wet wood will take heat out faster and if if is hot outside it will bring heat in faster. What they are looking for is how different the wet wood areas are from areas that cannot be wet. Sometimes the difference will be large, other times very small.

As to the database - those and other factors apply.

There should be plenty of videos on YouTube that show typical results.

 

[IRstuff]

Agree, you're not seeing moisture, per se, but the difference in thermal emission, which is either emissivity or temperature differences. Water in the LWIR is a pretty decent blackbody

TTFN (ta ta for now)
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[Ron]

I have been using thermal cameras for building envelope work for over 30 years. They can be great tools, but can be misleading as well, particularly when used by those who don't know their limitations.

As others have noted, they don't find moisture. They find, perhaps, indications of moisture based on a thermal signature. They are, at first, visible thermal anomalies that have to be verified by a secondary means, preferably by destructive observation and sampling. A secondary means can also be another nondestructive approach (capacitance meters, nuclear moisture gage, etc.); however, to get irrefutable evidence, cutting into the material and observing and sampling materials for laboratory determination of moisture is preferred.

In a building it is easy to get a lot of false anomalies. As an example, you use a thermal camera to observe an exterior wall and you see a thermal indication. Is it moisture or is it some appliance or device on the interior that is causing the wall to heat up? Each of the anomalies can be a rabbit hole that has to be run down.

As for cameras, there are lots of them on the market....some good, some not so much. I have a FLIR camera that costs about $20,000. It is pretty good and I get it calibrated periodically, which costs about $500 to $1000 each time. Not a cheap process but if I am putting my reputation out there based on its use, I want it (and me!) to be right!