Thermography Cameras – Opgal Optronic Therm-App & Seek Thermal Compact Review
For the original German review, see here.
They are essential for our reviews: Temperature measurements at the case surface show how well a smartphone, tablet or notebook can handle the heat from the components. Because of the trend towards thinner chassis constructions, critical hotspots are not limited to powerful gaming laptops anymore – one prominent example is the Snapdragon 810 from Qualcomm with its serious thermal issues. Several high-end smartphones (e. g. the HTC One M9) suffered from high temperatures and noticeable throttling under maximum load.
The complex heat development of a device can usually not be sufficiently displayed with individual measurement spots – even a few millimeters to the left or the right can completely change the results. The solution for the problem: An imaging method that provides a high-resolution image of the temperature profile over the whole surface. We want to use this article to have a look at the theoretical basics and the practical use of so-called thermal imaging – and expand certain future reviews with corresponding images and analyses.
We will present different smartphone solutions for the creation of thermal images over the next few weeks and have a closer look at the handling, the precision and the price-performance ratio.
The physical principle behind thermography, also known as thermal imaging, has been familiar for around 200 years: Every object that has a temperature above absolute zero emits energy in the form of radiation – a nice example is the colorful glow from a hot piece of metal. The wavelength of the emitted radiation depends on the temperature: The cooler a body, the bigger the wavelength. Common ambient temperatures, often assumed at 300 K (26.85 °C), reach about 10 µm (highest radiation), which is already in the infrared range and therefore not visible. Common infrared cameras use special lenses that can only be passed by wavelengths between around 7 and 14 µm.
The radiation power is proportional to the fourth power of the temperature of a body (Stefan-Blotzmann law) – connected with an additional natural constant it is possible to determine one value from the other. This correlation works for idealized black objects that absorb the radiation that hits them completely (emissivity 1). This value is usually a bit lower in practice and is somewhere in the range between 0.9 up to 0.95 for non-metallic or very reflective surfaces. If this value is not known and the thermal camera is not set up properly, there can be significant deviations between the measured temperatures.
After the camera has calculated the temperature for every point, it still has to create an image that can be interpreted by the human eye. This is done via false-color technology, which means every temperature value will be assigned with its own color or shade of gray. The most common approach is to use blue colors for cool areas, green and yellow for average temperatures and red colors for warm areas (rainbow color palette). It is also possible to limit the colors to shades of red and yellow (glowing colors) or use a high-contrast black and white picture.
Thermal Image Cameras in Practice
Opgal Optronic Therm-App
Our first review sample is from the Israeli company Opgal Optronic Industries and has the designation Therm-App (www.therm-app.com). You should not be confused by the name, since it is not only an app, but a complete thermography kit for Android devices: The scope of delivery includes a compact infrared camera, which weighs just 120 grams including the mounting and has the dimensions 4.5 x 5.7 x 4.0 centimeters. Furthermore, you get three different angled Micro-USB cables for the connection between the smartphone and the camera, a detachable handle bar as well as a pretty short manual. The price for the whole set is $939.
Despite the small size, the Therm-App creates comparatively high-resolution thermal and night vision images with 384x288 pixels (many similar expensive or cheaper rivals have a much lower resolution), but the frame rate is limited to just 8.7 fps. The company also offers a high-end version with 25 fps, but this was not available for our review. You get a fixed focal length at 19 mm with a manual focus that can be replaced by several other lenses (6.8/13/35 mm focal length), which are available for prices between $189 and $750.
Installation and Set-up
The first set-up of the Therm-App is, fortunately, pretty simple and should not be a problem for any Android user. First, you have to download the free Therm-App application from the Play Store. After that you mount the camera on the smartphone via a screwing mechanism and put in the USB cable. The latter is used for data transfer as well as the power supply of the camera. The manufacturer specifies a consumption of less than 0.5 Watts.
Opgal Optronic has an official support list with roughly 30 smartphones on it, including current models from series like Samsung Galaxy, HTC One or LG G. However, pretty much every Android smartphone with USB OTG support running Android 4.1 or higher should be compatible with Therm-App. We used a Samsung Galaxy S4 running Android 5.0.1 for the review; we never encountered any crashes or other problems.
Just as easy as the installation is the configuration and the use of Therm-App. You can see a real-time thermal image immediately after the launch of the app, and you just have to adjust the sharpness via focus ring. A scale at the side gives you information about the minimum and maximum temperatures in the current picture, and an optional cursor shows the temperature in the center with an accuracy down to 0.1 °C. However, the manufacturer specifies the measuring tolerances at ± 3 °C or ± 3%, so you should be careful with the decimal places – also considering possible uncertainties of the selected emissivity. Above and below the picture are buttons to take pictures and videos (h.264 with sound), a link to your pictures as well as the options, where you can switch between the thermal and night vision images. You can also use different color profiles or change the previously mentioned emissivity.
Menu and Settings
Thermal and night vision images basically use the same principle that we described in the basics. While the thermal imaging is, however, supposed to enable a very precise analysis of temperature developments, the night vision function is optimized for a very high contrast ratio to recognize people and animals. We focused on the thermal images during the test and analyzed the heat development of HP’s business detachable Elite x2 1011 G1. The load pictures in particular clearly show a local hotspot at the upper right area of the back, which is obviously caused by the Core-M SoC that is located at this spot. Also interesting: The background illumination of the display, which is visible as a thin red stripe on the lower display frame, is also a significant heat source at the highest brightness setting. The keyboard dock, however, stays evenly blue, because it does not contain any hardware and therefore no heat sources.
A direct comparison with an infrared thermometer Fluke 62 Max shows that the temperatures of Therm-App differ by around two Kelvin, which is still acceptable. Even a slightly deviating emissivity can create similar or even bigger differences.
Seek Thermal Compact (Android)
Review sample number two is the Seek Thermal Compact (http://www.thermal.com), a conceptionally very similar thermography solution for Android and iOS smartphones (either/or, has to be selected during the purchase). Contrary to the Therm-App, which is also very compact, the camera from Seek is almost tiny: Four and a half centimeter wide, around two centimeters high and deep with a weight of just 12 grams – the term ultraportable really fits here. An additional mounting is therefore not necessary, but the micro-USB connector is sufficient for the secure connection between the measurement device and the smartphone. You should, however, ensure that the wide side of the micro-USB port of your smartphone is faced towards the back, so that the orientation of the camera is correct. Otherwise, you will have to use an additional adaptor cable. The support list from the manufacturer includes, among others, the Samsung models Galaxy S3 up to S6 as well as Note 2 up to Note 4, the Motorola Moto G and Moto X as well as Apple’s iPhone 5 and newer; but the majority of Android smartphones with at least Android 4.3 and USB-OTG support should work with the Seek Compact.
At $249, the Seek Compact only costs a fourth of the Therm-App – technical cutbacks can hardly be avoided. This is most noticeable at the sensor resolution, which is just 206 x 156 pixels instead of 384 x 288 pixels. The refresh rate is specified with less than 9 Hz. The lens with a fixed focal length and a manual focus is similar to the Therm-App, but it cannot be replaced. Besides the standard model with an opening angle of 36°, the manufacturer also offers a smaller 20° version for an additional 50 Euros. Both models are specified for a surprisingly wide operating range between -40 up to +330 °C; but the spec sheet does unfortunately not list the measuring accuracy depending on the temperature. It is generally not possible to get detailed measurement results for every individual pixel.
Installation and Set-up
The solution from Seek should not be a big challenge even for thermography newcomers: Load the "Seek Thermal" app from the Play Store, attach the camera and you are ready. The lack of cables and mountings makes the handling even easier and ensures that the Seek Compact is ready within a few seconds. You should, however, be careful not to overstress the delicate USB connection – you might damage both the smartphone and the camera in the worst case.
Similar to the Therm-App, we tested the Seek Compact in combination with a Samsung Galaxy S4 running Android 5.0.1, but encountered some smaller bugs. The camera occasionally only showed a black picture after we switched to the home screen, which could only be solved by a reattaching of the camera or several restarts of the app. Pictures were sometimes also stored a bit distorted, even though we selected the correct 16:9 screen ratio. Still, none of these issues are really serious.
The main menu directly after the launch of the app is similar to Therm-App and is dominated by the thermal view with several control elements around it. Besides the buttons for pictures and videos, a shortcut to the gallery as well as several options you find the so called "Heat+" mode, which has a handy split screen view of the real-time image from the smartphone as well as the thermal camera.
Menu and Settings
As expected, the picture quality suffers noticeably from the pretty low sensor resolution.While this is not a big problem when you take pictures of large objects with even temperature developments, it can make detailed analysis of delicate structures – like our test object HP Elite x2 1011 G1 – much harder. The dynamic range also reveals some weaknesses, which means small temperature differences can quickly become blurred. Still: The performance is more than sufficient for the search of thermal bridges at houses – and the quality is actually decent when you consider the price.
The Seek Compact might lack hardware specs, but it offers a lot of features in return. Nine different color modes, overlays of min/max cursors (even though they tend to move so far to the bottom that you cannot see the displayed values anymore) and a handy limit value mode that highlights areas based on temperature values to help the user.
Despite the description in the help, we did not find the function to set the emissivity manually. The displayed temperatures suggest a useful standard value between 0.9 up to 0.95, but some certain surfaces might need a manual adjustment. This means the See Compact would not work well with metallic-glossy materials, for example.
Compared to our infrared thermometer, the Seek Compact usually shows slightly lower results, but the difference is usually at around 2 Kelvin or less. However, because of the pretty low resolution, local maximum or minimum temperatures cannot be ruled out.
Thermal imaging is not only interesting for thermal insulation of buildings or industries but also in the IT segment for notebook and tablet tests, for example.
The smartphone connection does not only mean that modern thermal cameras like Therm-App can be used very easily, but the prices are getting lower and (more) affordable as well. Almost $1000 is certainly no bargain, but you get a well-built and technically convincing product in return. We will see how Therm-App works compared to other rivals over the next couple of weeks – but we could not find any serious issues during our comprehensive review.
Considering the price of just $250, the Seek Compact is hardly a direct rival for the Therm-App that is almost four times more expensive. It is therefore more of an inexpensive alternative for simpler scenarios. It will pay off for private users that just want to have a look at the thermal insulation of their house or make first experiences with thermal images – professional users on the other hand won’t be very happy with the lower resolution and the limited dynamic range.