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Emissivity error compensation (IR gun error)

PostPosted: Wed May 15, 2019 8:29 am
by kingofnobbys
refer to information : viewtopic.php?f=34&t=239064&p=1833542#p1833542
and this explain more : viewtopic.php?f=34&t=241233
It is possible to compensate for emissivity errors but the calculations involved will be beyond most reptile keepers who don't have the necessary physics or engineering education , the existing IR gun is likely 20 to 30 degrees Celsius out when reading the surface temperature the "NON STANDARD SURFACE (which has a emissivity significantly different to the standard e (gun) = 0.95 found with cheap IR guns who have no emissivity adjustment).




For those who have some university physics and engineering the brief explanation is as follows :
the degree to which errors in emissivity settings will affect temperature and T_error (error in temperature) accuracy even not often understood by many professional physicists , engineers , chemists and thermographers .
Little wonder lay people who have no professional training and simply assume the IR gun is going to give accurate temperature readings for all surfaces measured get this wrong .

The Stefan-Boltzmann Law gives the radiated infrared energy emitted by a target surface and shows this is exponentially related to the absolute temperature of that surface.
The equation is E_b=εσT^4 where ε is the surface emissivity and the true surface temperature is calculated using this equation
Image

Re: Emissivity error compensation (IR gun error)

PostPosted: Wed May 15, 2019 1:28 pm
by Aaradimian
Oooh, something science-y AND beardie related that I can nerd out on. Thanks king!

Re: Emissivity error compensation (IR gun error)

PostPosted: Wed May 15, 2019 1:39 pm
by CooperDragon
There is an emissivity chart linked in the old thread, but here's another if you want to reference http://www-eng.lbl.gov/~dw/projects/DW4229_LHC_detector_analysis/calculations/emissivity2.pdf

The .95 default setting is pretty good for a lot of the surfaces in the tank like ceramic floor tile, glass, water, and opaque plastic but not accurate for other things. Usually close enough to get a good idea of what the temp gradients are though.

Re: Emissivity error compensation (IR gun error)

PostPosted: Wed May 15, 2019 11:53 pm
by kingofnobbys
CooperDragon wrote:There is an emissivity chart linked in the old thread, but here's another if you want to reference http://www-eng.lbl.gov/~dw/projects/DW4229_LHC_detector_analysis/calculations/emissivity2.pdf

The .95 default setting is pretty good for a lot of the surfaces in the tank like ceramic floor tile, glass, water, and opaque plastic but not accurate for other things. Usually close enough to get a good idea of what the temp gradients are though.


If your surface has an emissitivity within the range 0.85 to 0.99 for a IR gun with an unchangeable preset builtin emissivity setting of 0.95 you can expect to be getting temperature reading within roughly 10% of the true temperature. ie Gun says 100F , surface has emissivity 0.85 , likely error is about 10F.
I'd be conservative and take that to mean my temperature is most likely somewhere between 100F and 110F , and adjust my heating accordingly if the aim is 100F , perhaps splitting the difference and using the IR gun (if I have no other option) to set up a temperature at 95F say ( to compensate for the emissivity error ).

I have an even more comprehensive emissivity table in my Perry's Chemical Engineers' Handbook , also a copy of the CRC Handbook of Chemistry & Physics , and the HRC Survey of Emissivities in my private professional library in my study as well as conference papers , physics and engineering journals ( I literally have 4 filing cabinets full of engineering and scientific papers and reports and journals , and a wall of bookshelfs overflowing with engineering, math, physics, chemistry and computer engineering books ) .
The best table and compilations of emissivities as functions of temperature for industrial materials that I've seen I was given by AGEMA and LAND INFRARED in their training courses for thermographers and their fixed , scanning and mobile system manuals. This was back in the 1990s when I was the inhouse thermography & pyrometry guru at Newcastle Steelworks and then OneSteel's Rolling Mills and developed a radiation compensated pyrometry system for use inside bloom and billet reheating furnaces with heating and soaking zone gas temperature between 1100 and 1350 degC ( where radiation effects become extreme and must be compensated for ) .

Re: Emissivity error compensation (IR gun error)

PostPosted: Thu May 16, 2019 8:38 am
by Aaradimian
For those gas temp. readings, was it a single-element gas or air? If air, did you have to average the readings out to account for the different elements (nitrogen, oxygen, etc.) or is that not that big of a deal? I'm curious because I'm going to be taking a course on space launch & re-entry in the coming year, and of course frictional/secondary heating vs. spacecraft materials will be covered. Since atmospheric composition and density varies with altitude, I'm wondering if it'd be of value for me to read up a little on thermal emissivity of different gases ahead of time. Secondary (radiative) heating as the gases pass the airframe near the boundary layer are big deal, apparently.

Re: Emissivity error compensation (IR gun error)

PostPosted: Thu May 16, 2019 10:48 am
by kingofnobbys
Aaradimian wrote:For those gas temp. readings, was it a single-element gas or air? If air, did you have to average the readings out to account for the different elements (nitrogen, oxygen, etc.) or is that not that big of a deal? I'm curious because I'm going to be taking a course on space launch & re-entry in the coming year, and of course frictional/secondary heating vs. spacecraft materials will be covered. Since atmospheric composition and density varies with altitude, I'm wondering if it'd be of value for me to read up a little on thermal emissivity of different gases ahead of time. Secondary (radiative) heating as the gases pass the airframe near the boundary layer are big deal, apparently.


It was a high temperature mix of air and combustion products ( coke ovens gas mixed with blast furnace gas , and later we converted to natural gas as the fuel) , we tried to keep the furnaces slightly superstiochiometric ( excess O2 about 2% ) and it was necessary run the furnaces so the pressure in the furnaces was always slightly higher than atmospheric.
Yes there were issues with variability of the gas mix driven by variations in fuel gas composition especially when we were using COG and BFG and a mix of COG & BFG especially during planned and unplanned delays (in the rolling). Transparency and luminousities of the flames were highly variable as a consequence .
Another complication was we upgraded the burners to prepare for the change over to NG as well and this made a significant change to the gas flow / flame dynamics in the furnaces that had to taken into account and the higher turndown characteristics came into play. That was another project I was responsible for engineering.
I also drove a project to improve the hearth and walls and roofs and burner walls refractories and this changed the emissivities of the radiating faces and viewfactors somewhat as well, another complication that needed to be taken into account.

No ballistic effects here , an entirely different situation to what your cause will cover. Ballastic and hypersonic projectile / vehicle thermal effects are all driven as you say by friction.

You'd be better placed to revise any studies you'd done on thermal physics (radiation and dynamics of conduction heat transfer) , high velocity fluid-dynamics, materials engineering (refractory and wear resistant materials), and bone up on your multivariable calculus and partial differential equations, and multivariable (MIMO) and model based control systems. If you don't have firm grip on these you are likely to find yourself out of your depth.

Re: Emissivity error compensation (IR gun error)

PostPosted: Thu May 16, 2019 12:31 pm
by Aaradimian
kingofnobbys wrote:
You'd be better placed to revise any studies you'd done on thermal physics (radiation and dynamics of conduction heat transfer) , high velocity fluid-dynamics, materials engineering (refractory and wear resistant materials), and bone up on your multivariable calculus and partial differential equations, and multivariable (MIMO) and model based control systems. If you don't have firm grip on these you are likely to find yourself out of your depth.


Thanks for the suggestions! Should be a fun class... :)

Re: Emissivity error compensation (IR gun error)

PostPosted: Thu May 16, 2019 11:05 pm
by kingofnobbys
Aaradimian wrote:
kingofnobbys wrote:
You'd be better placed to revise any studies you'd done on thermal physics (radiation and dynamics of conduction heat transfer) , high velocity fluid-dynamics, materials engineering (refractory and wear resistant materials), and bone up on your multivariable calculus and partial differential equations, and multivariable (MIMO) and model based control systems. If you don't have firm grip on these you are likely to find yourself out of your depth.


Thanks for the suggestions! Should be a fun class... :)


Is it a 1 term class , or a 1 trimester class , or a 1 semester or full year class ? Undergraduate or postgraduate (ie 300, 400 (undergrad level) , or 500 or 600 (postgrad level) program by a university or a company run course ? ( In my experience that inhouse classes that typically run for a week or fortnight , (all day every day) are less rigorous in general than a full fledged university classes ).

The AGEMA and LAND INFRARED courses were run at their research labs and ran for 1 month and were very in depth and rigorous and class sizes were limited to 10 participants . My company flew me overseas to "be trained up" after I convinced them that we needed to use thermography in our research and development programs and needed to improve our remote temperature sensing systems (update and improve and expand).

Re: Emissivity error compensation (IR gun error)

PostPosted: Fri May 17, 2019 7:40 pm
by Aaradimian
kingofnobbys wrote:Is it a 1 term class , or a 1 trimester class , or a 1 semester or full year class ? Undergraduate or postgraduate (ie 300, 400 (undergrad level) , or 500 or 600 (postgrad level) program by a university or a company run course ? ( In my experience that inhouse classes that typically run for a week or fortnight , (all day every day) are less rigorous in general than a full fledged university classes )


It's a 300-level for an undergraduate degree, so I don't anticipate having to use the heavy-duty maths in it. The pre-reqs are only Calc II and Physics I, and it's 16 weeks.

Re: Emissivity error compensation (IR gun error)

PostPosted: Sat May 18, 2019 1:21 am
by kingofnobbys
Aaradimian wrote:
kingofnobbys wrote:Is it a 1 term class , or a 1 trimester class , or a 1 semester or full year class ? Undergraduate or postgraduate (ie 300, 400 (undergrad level) , or 500 or 600 (postgrad level) program by a university or a company run course ? ( In my experience that inhouse classes that typically run for a week or fortnight , (all day every day) are less rigorous in general than a full fledged university classes )


It's a 300-level for an undergraduate degree, so I don't anticipate having to use the heavy-duty maths in it. The pre-reqs are only Calc II and Physics I, and it's 16 weeks.


Things must be different in US universities. I'm not sure what the content of Calc II is .

Here all engineers are required to take a full year 200 level topics called Vector Calculus and Differential Equations , and at least a semester of advanced Linear Algebra and of Complex Analysis.
All engineers are also required to take engineering 300 and 400 level courses on control engineering (including use of laplace, z and q transforms to model and solve systems including coupled MIMO systems and Model based systems.

300 level engineering and science topics are very rigorous here.

You can expect to use vector calculus and differential equations ( ordinary and partial ) , advanced linear algebra and have a good basis in advanced control theory (to be able to work out stability criteria etc).
Bone up on your Simulink & MATLAB programming and C++ or Fortran Nag library skills.

Re: Emissivity error compensation (IR gun error)

PostPosted: Sat May 18, 2019 6:25 am
by CooperDragon
The terms vary between colleges - there isn't a set standard that I know of. Some places have Calc 1 and Calc 2. Some have it broken down further into 3 and 4 as well. My school had Calc 1 and Calc 2 and as I recall (this was quite a while ago now) Calc 2 included things like partial derivatives, dot and cross products, polar coordinates, projectile motion. Ugh I just gave myself nightmares thinking about it. Differential Equations was it's own course that came after Calc 2. I remember having to take a computer science class along side it that focused on cryptography and algorithm design. What a mess that was!

Re: Emissivity error compensation (IR gun error)

PostPosted: Sat May 18, 2019 9:37 am
by Aaradimian
Yes, sounds like there's definitely some variance. The course content in your 300-equivalent courses would be more like what I'd expect in a master's program. This is the next rung down, a batchelor's program. Basically, it's the bridge between what we learn as kids, young adults and a specialization in a particular area of study. Partial differential equations & such would be roughly "Calc III", with Calc II focusing on applications of integration, and Calc I on those of differentiation.

Re: Emissivity error compensation (IR gun error)

PostPosted: Fri May 24, 2019 7:57 am
by kingofnobbys
guide to good technique :
Make sure the gun is used in such a way that :
>> the emissivity has been adjusted to e of the surface (if this option is available)
>> the gun is angled in such a way the light (and IR) from the baking globe is not being reflected into the gun --> will result in a much higher reading
>> Conduct the measurement perpendicular to the material’s surface whenever the emissivity is less than approximately 0.90. In all cases, do not exceed angles greater than 30 degrees from perpendicular
>> the hot spot should full the sensor spot size, ie 1" diameter at 12" distance.

Re: Emissivity error compensation (IR gun error)

PostPosted: Mon Jul 29, 2019 7:40 pm
by CooperDragon
Moved by moderator to enclosures to advanced lighting/enclosures