Measurement Science: Taking Accurate IR Thermal Readings

If you thought that buying and unpacking an expensive infrared camera was all that it took to perform professional-level measurements, then it's time for a little lesson. We’ll share some of the knowledge that goes into generating accurate results.

Understanding how infrared technology works is one thing. Knowing how to use it correctly to get the right measurements is another. Follow along as we explain the difference between a well-planned infrared measurement and simply pointing an infrared camera at something, since doing the latter usually doesn't get you valid results, no matter what some people say. It doesn't matter if you're talking about graphics cards, processors, motherboards or laptops, the general principle is always the same.

Without a solid handle on the theoretical fundamentals, there's no telling what your measurement might mean. But it's usually not what you intended. That's why we'll spill the beans on our measurement equipment, and then show you what can go wrong. That's good context for comparing the results on other hardware sites, along with their methodologies.

Along the way, you'll learn why we're not using convenient handheld equipment, but instead employ a camera that needs to be installed in a stationary position. It features high-quality interchangeable lenses that can be adjusted based on the subject in question (distance, size of the target to be measured and so on). Doing it this way does require additional time to install and calibrate everything, but you directly benefit from the better results that this process yields, and that's what's most important.

Before we get to the actual measurement methodology and assembly, we'll take a look at the Optris PI640. This particular model is not very well known, which is a shame since it yields reliable measurements when it's used correctly. It's also less expensive than some handheld alternatives, and it provides more options and higher-quality results. All of this is due to it being an industrial solution that is usually permanently installed. The video below shows just how flexible the camera is.

High-end hardware like this doesn't just require a lot of expensive development and production efforts, but also needs regular calibration and maintenance. Without them, even the greatest measurement equipment isn't going to be of much use; daily use changes the exact setup, and aging components do their part to invalidate the results. We try to keep our configuration up to date. That's why we recently changed from the PI450 to the PI640. The latter provides us with even more options.

In case you're interested, we're including a few photos from our development, production and maintenance below. We apologize that we can't show certain things due to their proprietary nature or them being trade secrets, even if they would be interesting to see.

Here's an overview of the technical specifications, before we get to the actual measurements.

Optris PI 640 Infrared Camera Technical Specifications
DetectorFPA, Uncooled (17μm x 17μm)
Optical Resolution
640x480
Spectral Range
7.5 – 13 μm
Temperature Ranges
–20 ... 100 °C
0 ... 250 °C
150 ... 900 °C
Frame Rate
32Hz
Optics (FOV)33° x 25° FOV / f = 18.4 mm or
60° x 45° FOV / f = 10.5 mm or
90° x 66° FOV / f = 7.3 mm
Thermal Sensitivity (NETD)75mK
Accuracy±2 °C or ±2 %, whichever is greater
Interface
PC interface: USB 2.0
Process interface (PIF): 0–10V input, digital input (max. 24V), 0–10V output
Enclosure (Size / Rating / Weight)46mm x 56mm x 90mm
IP 67 (NEMA 4)
320g, Including Lens
Shock / VibrationIEC 60068-2-27 (25g and 50g)
IEC 60068-2-6 (sinus shaped) / IEC 60068-2-64 (broadband noise)
Included

USB camera with one lens
USB cable (1m)
Table tripod
Standard PIF with cable (1m) and terminal block
Software package Optris PI Connect
Hard transport case


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24 comments
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  • Aris_Mp
    Very nice and highly informative article. Thanks Igor!
    3
  • samopa
    Do they have some kind of API, to be connected to other system without using their proprietary software ?
    0
  • AndrewJacksonZA
    Wow, thank you very much for a _very_ informative article Igor.
    0
  • dmnwlv
    Respect to tomshardware in its quest here to form a more complete picture in hardware tests and for presenting verifiable (factual) data in its reviews.
    I never bothered with all other sites' temperature charts/reviews on gpus ever since toms started doing this.
    1
  • FormatC
    Anonymous said:
    Do they have some kind of API, to be connected to other system without using their proprietary software ?


    They have an API and a helpful documentation too. :)
    1
  • Flying-Q
    I like all the isolation and standardisation you use for consistent, repeatable and accurate measurement. I have a question though: would a cowl over the CPU, chipset and memory make any difference to preventing reflected heat contribution from those components?
    1
  • FormatC
    Only, if the waves goes in the same direction. Upgoing heat is no problem (90° crossing).
    I tried it to cover it with a thick, black foam plate - no difference. :)
    1
  • dr3cks4u
    Very good article, thanks for that. I´m sure a lot of people don´t know how time-consuming this kind of measurement is. Question @ Igor: Is the emissivity of the used lacquer constant across the electromagnetic spectrum (=grey body) or is it just known for the camera´s spectral range (7,5-13,0 microns)?
    0
  • FormatC
    Only for this range. It was calibrated for me in Asia. :)
    1
  • dr3cks4u
    Quote:
    Only for this range. It was calibrated for me in Asia. :)


    Thank you ;)
    0
  • FormatC
    A lot of things I can calibrate by myself, but the lacquer is a little bit too difficult.
    We had to measure both, emissivity and transmittance. You need a lab for such things.
    BTW: I'm using a very good air brush to be sure to hold the thickness.
    0
  • Alan_35
    Nic article. I use my Therm-App and they also provide API
    0
  • Onus
    There are still people who think it is ok to run an eight-core FX on a 760G or other cheap AMD motherboard. Could you take a few shots of the VRMs on such boards, to show people why this is a bad idea? Only a couple ought to be enough
    Anyway, that's a nice piece of gear; looks to be around $6k, so no wonder why not everyone and his brother uses one, and why TH continues to stand above the competition.
    0
  • FormatC
    Anonymous said:
    There are still people who think it is ok to run an eight-core FX on a 760G or other cheap AMD motherboard. Could you take a few shots of the VRMs on such boards, to show people why this is a bad idea? Only a couple ought to be enough...


    "Cheap" 970 mainboard (from my Wraith cooler review) and FX 8370:

    0
  • Onus
    I thought the 970 Gaming was actually a better board; looks like not...
    For 970, I had in mind their 970-G4x boards; anyone's 760 or 780 could be used.
    For the sake of fairness, I must point out that as poor as I believe those are, it is remarkable how much nicer high-end MSI boards are. I've actually come to look forward to seeing an MSI board among my review samples. Whether or not it deserves an award, I'm generally able to find something nice to say about it.
    0
  • FormatC
    I've stressed the MSI 970 Gaming with a FX 9590 @5 GHz (and killed a 2 years old Corsair H100i with him). But the mainboard is still alive :D
    0
  • Onus
    Hmmm, someone needs to invent a VRM heatsink that will accept a single strip of bacon or a sausage link.
    0
  • FormatC
    Anonymous said:
    Hmmm, someone needs to invent a VRM heatsink that will accept a single strip of bacon or a sausage link.


    I does it a few years ago with VGA cards!

    Square Egg:


    Hot Dog:


    Fondue:


    The complete review, heating benchmarks included (in German, but funny):
    http://www.tomshardware.de/HD6990-GTX590-Corsair-Obsidian-800D,testberichte-240761-10.html
    1
  • alidan
    how much did the camera cost? all im able to quickly find online is a spec sheet.
    0
  • FormatC
    Anonymous said:
    how much did the camera cost? all im able to quickly find online is a spec sheet.

    With one lens:
    http://www.optris.com/product-configurator-pi-640
    0