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
Spectral Range
7.5 – 13 μm
Temperature Ranges
–20 ... 100 °C
0 ... 250 °C
150 ... 900 °C
Frame Rate
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
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)

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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