Thermal Imager: What Is It and What Do You Do with One?

Many people have probably heard the name “thermal imager.” Some have probably seen one in movies or technical programs, but I doubt many people know what it is or how it works.
In this review, I’ll try to explain in simple terms what this device is.
As always, there’ll be a bit of everything: a description, a short test, and a teardown.

First, I should say that I’d wanted one of these for a long time, and just before New Year I finally decided to order one.
The thing is, these “toys” are very expensive. Since I was buying one for myself, I chose the cheapest option—and, of course, the simplest. Yes, around $300 is very cheap for a thermal imager; professional models start at several thousand dollars and go up from there.
The seller always has a discount, and it’s always about to expire :) But there’s a $6 coupon for purchases over $100, which is what I used. I asked for a slightly bigger discount, but no luck :(

Let’s start with a little theory.
Every object around us emits heat, provided its temperature is even slightly above absolute zero (-273 degrees). Yes, even an object at -100 degrees emits heat, strange as that may seem.
And since something is being emitted, we can see it if we want to. Of course, the human eye can’t see radiation in this range, so we need special instruments.

Most people have definitely seen and used non-contact thermometers. I did a review of one type.

The principle behind this kind of device is fairly simple. The thermometer’s sensor detects the thermal radiation from the object being observed and converts it into a temperature value we can understand.

Of course, you may be wondering how the device determines the temperature. I’ll try to explain.
Objects don’t just emit heat; they emit it at different intensities and, most importantly, at different wavelengths.
For example, the wavelength range of visible light is 380 to 740 nm (nanometers). Below 380 nm is ultraviolet; above 740 nm is infrared radiation.


At temperatures from -50 to +50 degrees Celsius, objects emit at wavelengths of 7 to 14 µm (micrometers); at around 100 degrees, the wavelength is already 3 to 7 µm.
The device “sees” this radiation and determines the wavelength at which the emission peaks, then gives us the corresponding temperature.

But with a thermometer, we can only measure the temperature at a specific point, while we’d like to see the whole object.
For example, like this:


Or like this:


There are several ways to achieve the desired result.
1. Scan the image with a single IR sensor or a line of sensors
2. Use an array made up of a large number of sensors.

The first option is very inconvenient because measurements take a long time, but image resolution is almost unlimited—the only question is how long the measurement takes. This approach also involves mechanical components.
The second option is simpler, but achieving high resolution comes with its own challenges.

Today, we’ll talk about the second option.
The sensor array consists of a large number of sensing elements that detect IR radiation focused by the lens.
Essentially, it’s a bunch of individual IR thermometers, without processing circuitry, assembled on a single chip.

The resolution of these arrays isn’t very high. The top-end arrays available to civilians have resolutions of up to 1280*720, but I’d rather not even talk about the price.
For more or less everyday use, simpler arrays are used, ranging from 60x60 to 384x288.

The intended use imposes limits on array resolution.
The thing is, we’re observing thermal radiation. Not only does the wavelength of IR radiation make it impossible to build a very compact array, but there are also problems with unwanted heating or cooling of neighboring pixels—we’re tracking thermal radiation, after all.
In other words, heat falling on one of the array’s sensing elements can warm up a neighboring element, causing an error.

An array that detects thermal radiation is called a bolometric camera.
In most common thermal imagers, these arrays are made up of a large number of microscopic thin-film thermistors.
The measurement principle itself imposes a second limitation: these arrays are slow, and thermal imagers usually record at 5-10 frames per second.
Thermal imagers with higher frame rates do exist, of course, but they cost more and are mainly needed for applications such as vehicle control systems.

A comparison of thermal imagers running at 9 fps and 30 fps.


I think the theory is a little clearer now (or at least I hope so), so it's time to move on to the practical side.
There are several types of thermal imagers.
Some are used simply for observation, for example by the military or hunters, or by emergency services.
These thermal imagers have a long operating range, but lack the features found in the second type.


The second type belongs to the measurement category. For these, temperature measurement accuracy, displaying readings at several points, and the ability to record photos or video are important, among other things.
These thermal imagers look a little different and are more like an enlarged version of a non-contact thermometer.


People also often confuse thermal imagers with night vision devices (NVDs).
They are completely different devices.
An NVD is usually an active device with a powerful IR illuminator and a camera that can see IR radiation reflected from objects in that range.
A thermal imager, on the other hand, is completely passive: it emits nothing itself (apart from the radiation produced by its electronics) and detects thermal radiation from the object.

Each device has its pros and cons. For example, a thermal imager can't see objects that are at the same temperature as the surrounding air, or sees them much less clearly. It also can't see objects behind glass, since ordinary glass almost completely blocks thermal radiation.
An NVD, on the other hand, can't see through fog, and warm and cold objects look almost the same on screen.

For comparison, here's a short video showing the difference.


That wraps up the introduction. Now I'll describe what I bought and received.
I'll cover the rest of the explanations and details as I go through the review.

As I mentioned in the introduction, I ordered the thermal imager just before New Year's. The seller shipped it in early January, but tracking didn't start until after January 9.
I picked it up from the post office on January 25. It came by regular China Post, not EMS, DHL, or anything like that.

To be honest, I expected it to be noticeably smaller, maybe 1.5–2 times smaller. So when they handed me a big box at the post office, I was a little surprised.
Of course, I could have checked the dimensions on the product page and estimated the box size, but it honestly never occurred to me.

The closest match in terms of specs, but from a well-known brand, is the FLIR TG165.

It arrived safe and sound; even the original packaging was undamaged.


The packaging is made of sturdy cardboard, so credit to the manufacturer for that. It survived the trip even though it was shipped in a regular bubble mailer.
There's some brief promotional information on top, along with a photo of the device.


The bottom of the box has a nearly complete list of technical specifications.
Screen size — 2.4 inches
Thermal sensor resolution — 60x60 (3600) pixels.
Visible-light camera resolution — 0.3 MP (actually less)
Camera field of view — 20 x 20 degrees; minimum distance to the object is 0.5 m (it works at shorter distances too, but the camera is focused for normal operation from 50 cm)
Thermal sensitivity (minimum detectable temperature difference) — 0.15 degrees Celsius.
Temperature measurement range — -20–300 degrees C.
Temperature measurement accuracy ±2% or ±2 degrees.
Emissivity adjustment — 0.1–1
Measurement rate — 6 times per second.
Detectable wavelength range — 8–14 µm
Focus — fixed
Color palettes — iron, rainbow, high-contrast rainbow, black and white, inverted black and white.
Display modes — five modes: camera only, thermal imager only, plus three blended modes.
Memory card — microSD
Photo format — BMP
Power — 4 AA 1.5 V batteries
Battery life — up to 6 hours per set
Auto power-off — 12 minutes
Certificate — CE (EN61326-1:2006). In fact, this certificate only covers EMC compatibility.
Dimensions — 212x95x62 mm
Weight — 320 g
Warranty — 2 years


When I opened the box, I felt like a Papuan. The thing is, it opens in a way I wasn't used to: it has a lid held on by a couple of small magnets.
I don't know where the manufacturer got this box, but when I opened it, I felt like they'd sent me a thermal imager for girls :)
The color of the box and the pretty holographic pictures (they seem to rotate when you change the viewing angle—nice) feel a little at odds with the purpose of the device.


The package contents are very sparse.
1. Device
2. Case
3. Strap for the case
4. Manual
5. 4 GB memory card.


I took a few photos of the manual's main pages; they might be of interest.
I also translated a few of the manual's main sections.
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As I mentioned above, it came with a case that looks like a holster.
The case is sturdy, and the top flap is secured with Velcro.


The case really is sturdy and well stitched.
It has a decorative zipper-like strip around the perimeter—that is, a regular zipper without a slider. Most likely, it's there to add rigidity.
There is a belt loop on one side, but it seems very flimsy to me.
Inside is a small, very shallow pocket.


A shoulder strap. Just a strap, really. Metal clips, sturdy, black :)


And here's the device itself. It really is quite large.


There are stickers on the sides with the device's name and a few key specs.


The front has the camera assembly, an LED, and a photo button.


The IR camera is at the top, with the visible-spectrum camera below it and the illumination LED underneath.
The LED is really tiny and weak. I honestly can't see the point of it, since it only lights things up from 20–30 cm away, and even then barely.
It's on in the photo on the right.
The LED is turned on by holding down the photo button; turn it off the same way.


The screen and keypad are on the back.


The screen is almost exactly the same size as a matchbox, both in length and width.
The keyboard is simple, with 6 buttons.
I briefly described the menu and select buttons in the section with photos from the manual; here I'll cover the rest.
The left/right buttons select the display mode: regular camera, IR, or image overlay.
The up/down buttons are a separate story. They're used to select and adjust settings in the device menu, but aren't used during normal operation.

That would be fine, except the up button decreases the value and the down button increases it.
How does anyone come up with something like that? It must have been deliberate, because it's just inconvenient.
The menu navigation itself works as you'd expect, but to increase a value you have to press the down button. Where's the logic in that?


When I ordered the device, I knew it was supposed to come with a memory card, but I couldn't see one.
At first I was a little confused, since the memory card slot is tightly covered by a rubber insert that matches the color of the body. From the outside, all you can see is the tab for opening it.
The body itself is gray plastic. The yellow parts in the photos are rubber, and fairly thick, as you can see in the photo with the memory card compartment open.
By the way, the included memory card isn't some no-name brand; it's a SanDisc, though only Class 4.


There's a threaded hole on the bottom for mounting the device on a tripod, the same size as the one used in photography equipment.
There's also a wrist strap attached there.


This is what the device looks like in your hand.
It sits comfortably, but without batteries it feels very light.


The device weighs just 227 grams without batteries (the manual says 320 grams).


The battery compartment cover fits very tightly and opens by sliding it down.


There are extra tabs on the sides of the cover that hold it closed.
To test the device, I bought four of the cheapest alkaline batteries I could find. But I'll say right away: it goes through them pretty quickly. You're better off using NiMH rechargeable batteries or modifying it to run on lithium.


The batteries fit very tightly. No, to be precise, VERY tightly. It's best to insert the pair that goes inside the body first, then the two at the bottom.


First power-on.
When switched on, the device displays a splash screen with a software loading bar, then starts up in the last mode you used. So if you had image blending enabled, that's the mode it starts in, which is very convenient.


When it's running, you can clearly see a slight lag in the IR camera image compared with the visible-light camera.
To show what I mean, I made a short video that demonstrates this drawback and also shows the startup, operation, taking a photo, and shutdown.


To be honest, I was surprised by the screen quality—or, more specifically, its viewing angles.
I expected it to look like an old LCD monitor, where you can only see the image properly when looking straight at the screen.
But in practice, the image is clearly visible from every direction except from above. Left, right, below, and straight on all look great.
The screen is also very bright. It was set to the minimum brightness of 10% by default, which is perfectly usable. I set it to 30%, which seemed better to me; at 100%, it's already very bright.

I noticed that installing the batteries changed the instrument's balance. The bottom became heavier, making it much more comfortable to hold.


Since I've already described the menu items, I'll go straight to some examples of it in use.
First, the built-in camera. I understand that it's only there to overlay the real image on the thermal image, but the results are rather disappointing.
That's because the instrument's screen is only 320x240 pixels, so the camera image has the same resolution.
It's only marginally suitable for taking photos, but it's perfectly adequate for actual use.
The camera's white balance seems to be set for natural light, because indoors the image starts to look green.


During use, I found that the images from the cameras don't line up.
That was to be expected, since the cameras aren't on the same optical axis; one is above the other.
In practice, the optimal distance is about 1-1.5 m, and the offset doesn't increase much as the distance grows.
In the photos, I tried all five display modes and also took a look inside the freezer (since I was already in the kitchen).
Here's a quick explanation of what's shown on the screen.
The temperature at the center of the image (the center marker) is shown at the top, with the battery charge on the right.
The minimum and maximum temperatures in the frame are shown at the bottom. Two additional markers (which can be turned off if needed) indicate these points. But the markers look identical, so when the temperature difference is very small, it's hard to tell which is which.
The current time is shown in the center at the bottom, with a color palette mode bar on the right (I'll demonstrate how it works later).

By the way, the instrument showed the temperature inside the freezer quite accurately, and I even used the tiny flashlight built into the thermal imager (without it, you couldn't see a thing).


For the next experiment, I made myself a cup of coffee with milk and decided to try out the different color schemes. Unfortunately, while I was experimenting and taking photos, the coffee went cold :(
I don't know the exact names of these schemes, but I'll start with the one I like best.
Next come black and white, and black-and-white negative.


And two more color schemes. I didn't take photos of all five options, just the maximum blend and full IR.


Next, I started experimenting with what I actually bought it for.
I work with all kinds of power supplies, as well as other electronics. And since all of it tends to generate a lot of heat, I decided that a simple non-contact thermometer wasn't enough—I wanted to get a better look at everything.
For the experiment, I used a well-known 24 V, 4 A power supply and photographed it from different angles and in different modes.
I had first warmed up the power supply by running 3.5 A through it.
These photos clearly show the vertical offset where one image is overlaid on the other.


Sorry for all the photos—I got carried away :)


I'll wrap up the photos here for now. There'll be more at the end of the review, but now it's time for something I really enjoy: taking things apart.

This device is intriguing, so there was no way I could leave it unopened. In fact, as soon as I got it, I wanted to see what was inside, just out of curiosity.
Of course, I had a pretty good idea of how it was put together and what I'd find inside, but imagining it and getting your hands on it are two different things :))))
The thing is, I'm used to judging the quality of instruments and devices not just by how they work, but also by how well they're built.


Only after all that did I remember that I hadn’t measured the current consumption. That’s especially important for a portable device.
Some of the measurements surprised me a little.
1. When switched off, the device registers nothing on the 200 mA range, meaning the current is less than 100 µA.
2. Current consumption while the device is booting is about 144 mA.
3. In normal operation at 30% brightness, consumption varies between 120 and 130 mA.
4. I went into the menu and tried setting the brightness to 100%, but above 80% the consumption exceeded 200 mA and overloaded the meter, so I left it at 80%.
5. At first, I thought consumption would be lower while the device was displaying the settings menu, since it wasn’t processing the camera signal. But it turned out that consumption is actually higher in the menu than in normal operation.
With the menu open and brightness at 80%, the current was 193 mA; after switching to normal operation, it dropped to 166 mA.
6. The most economical mode turned out to be thermal imaging, with the regular camera switched off.
While using the device, I also noticed that after switching from thermal imaging to any other mode, the previous image flashes up for a fraction of a second. It turns out that the regular camera is switched off in thermal imaging mode, which noticeably reduces power consumption.
At 30% brightness, consumption drops to 81 mA, so 6 hours of operation from a fresh set of good batteries is entirely realistic.


And finally, here are a few photos of various things I took while preparing this review.
But first, a comparison photo from before and after raising the camera.
Before on the left, after on the right.


1, 2. The electronic load in operation. You can see the heat from the heatsinks inside, even though they’re being actively cooled by airflow. The case is closed.
3. A 2.5 mm² cable heating up under a current of 20 A.
By the way, I noticed that you can see the heat distribution along the cable quite well.
4. Heating at the connector contacts from my previous review, with a current of about 20 A.


1, 2. The maximum specified measurement temperature is 300 degrees. In reality, the device measures up to about 320 degrees. The photo shows a cigarette ember in an ashtray.
The device kept trying to indicate an overload, so I had to find a position where it would show the maximum reading.
3, 4. The camera after a short photo session.
5. This is what the image looks like if you take a warm device onto the balcony when it’s -20 degrees outside.
6. And this is what an ordinary floor looks like, with no bright heat sources.


And that's about it. Now I can sum things up.
Pros
The device works perfectly
It proved stable in use, with no glitches or freezes
It has all the essential settings.
Good, sturdy construction
Can save photos to a memory card
Memory card included
Sturdy case included.
Good packaging.
Price: I couldn't find a cheaper option.

Cons
60×60 is really the bare minimum resolution. It would be better to have at least 80×80, and for genuinely comfortable use, you want 128×128 or higher.
The shutter button is a bit too soft.
The images from the cameras don't line up
The flashlight is more present than functional; it definitely needs reworking.
It runs on batteries; rechargeable batteries would be much more convenient.

My take: This device really sits somewhere between an advanced IR thermometer and a basic thermal camera. An image refresh rate of 6 frames per second is more than enough for most measurement tasks.
If you're choosing between a thermal camera with higher resolution and one with a higher frame rate, go for the higher resolution. That's what I'd choose now, at least.
I'm a little disappointed, personally. Of course, I knew what a 60×60-pixel image would look like, but I really would have liked more.
And what really gets annoying is that the images from the cameras don't line up.
I've gotten used to it, of course, but I think I'll modify the design to add an adjustment feature.
One thing to highlight about this thermal camera is that even this basic model is genuinely useful at work, especially when observing things in motion. You can simply inspect the same power supply from different sides and see how the heat is distributed, including the hot and cold spots.

I don't know if my review will be useful to anyone, since this is a very specialized device and even this basic model is fairly expensive.

I can already hear the question: why not get a Seek Thermal, which has a higher resolution?
The devices cost about the same. I wanted a complete, ready-to-use solution, whereas if I bought a Seek Thermal, I'd also have to buy a smartphone. Besides, as I understand it, it doesn't work with every smartphone. And then there's the hassle of buying one...
In short, my criteria were that it be a complete solution capable of displaying an object's thermal image, and the thermal camera reviewed here meets those criteria.

As always, I'm looking forward to your questions, additions, and just plain comments.
The IR photos are a bit repetitive, but I plan to use this device when putting together future reviews, so there'll be more photos :)