Which thermal imager to choose for an energy audit. How to choose a thermal imager for building inspections

Thermal imagers, or as they are also called, high-precision infrared temperature sensors, have found their application in almost all sectors of the national economy and industry. A thermal imager is a device that is capable of capturing infrared radiation from the body and converting it into an electrical signal, which in turn is converted into graphic information. We see the latter on the device screen. High-precision thermal imagers used for a variety of purposes and in different industries. Depending on the type of device, its accuracy, ergonomics, matrix size, display resolution and other characteristics, thermal imagers are divided into different classes.

Highly specialized thermal imagers perform their job well only under certain constant conditions and are cheaper than those that are universal. Therefore, when choosing a thermal imager, you must firstly carefully study the technical characteristics of the device, and secondly, decide on the tasks that it will encounter. Let's say, if you need to analyze the thermal insulation of your home, there is no point in taking a device with an upper limit of measured temperatures of 1000 degrees. And at the same time, if you are going to record changes in your vehicle fleet, it makes sense to take a device with a higher upper temperature limit. In general, in order not to make a mistake when choosing a thermal imager based on the temperature range, you should always remember that the operating range should cover the temperature of the object by 25%. Thermal imagers allow you to quickly detect heat leaks from a building in use, as well as cold leaks from a refrigeration system. At the same time, thermal imagers are actively used to find faults in electrical networks and connections, and to detect breakdowns in the operation of electrical appliances. An increase in temperature both in the electrical connection and in dissimilar electrical elements indicates that they are not working properly and may completely fail.

Operating principle of a thermal imager

Modern thermal imagers are non-contact measuring devices that measure the temperature of an object from a safe distance. But how do we obtain information about the temperature properties of certain objects at a distance? The thing is that any object in nature that has a temperature above absolute zero (-273 degrees Celsius) emits a special type of radiation - infrared waves, or, in more understandable terms, thermal waves. This radiation is emitted by both the hot metal and the human body, but the human eye is not able to register it. Later, devices appeared that could do this, called pyrometers, the first such portable device developed by Wahl Instruments Inc. more than 50 years ago. Since then, the technology for recording thermal radiation has improved and become available to almost everyone. And as before, choosing a thermal imager is a very important step, since non-contact sensors are mostly highly specialized and each has its own application.

A modern thermal imager is an optical-electronic device that detects infrared radiation invisible to us using an optical system. As a rule, the optical system is represented by a lens. In the receiver, this signal can be processed into an electrical one. Next, the device processes the electrical signal and prepares it for display and display. Mainly in the form of digital and graphic information. It should be noted that the higher the power of the radiation flux, the higher the voltage of the electrical signal processed by the thermal imager. The output image on the device screen shows the temperature distribution over the area of ​​the measured object. Each temperature corresponds to a specific color, so the complete picture is a collection of temperature points painted in one color or another. Typically, thermal imagers use light colors ranging from blue, which colors the cooler areas of objects. Thus, using a non-contact temperature meter, you can determine the exact location of overheating, or record the exact temperature value in different parts of the object. Modern digital thermal imagers have a matrix similar to that found in digital cameras. But the main difference is that each point of the matrix shows not the color but the temperature of a given point of the object, but the full image - a raster image of the temperature distribution over the object.

The main criteria influencing the choice of a thermal imager

The first thing you need to do is decide on the type of device and answer a few basic questions, and only then choose a specific thermal imager model. Depending on their technical characteristics, certain models are exceptionally good as construction thermal imagers or security thermal imagers, or as thermal imagers for hunting. It all depends on their features and characteristics. When choosing a thermal imager, you should pay attention to the following key points:

1. The material from which the test object is made
2. Average temperature of tested areas
3. Measuring distance to objects
4. Environment in which the device will operate (transparency, humidity, ambient temperature)
5. Temperature sensitivity of the device
6. Measuring speed
7. Detector size and resolution
8. Information display mode
9. Functional equipment

Why is the material from which the test object is made important? The thing is that different materials emit waves of different lengths. For example, metal emits short waves, and other lighter materials emit long waves. Not all thermal imagers are capable of recording both short and long waves of thermal radiation. Most of them test objects only in a certain spectral range, that is, designed to work with specific materials. But, there are also more universal devices that operate in a wide range of frequencies. For example, a professional thermal imager for construction FLIR B660 operating in the range of 7-13 microns.

Operating temperature range of the thermal imager

When choosing a non-contact temperature sensor, it is also important to pay attention to the temperature range that it can record. Also, first of all, you need to compare this range with the temperature of the tested object. If, for example, you measure a temperature of 200 degrees, then there is no point in taking a device with a range from 500 to 1000 degrees. Modern thermal imagers record both low and very high temperatures (from -50 to +3000). Many devices are designed specifically to monitor refrigeration systems or heated objects. In the first case, they operate in a low-temperature range, and in the second, in a high-temperature range. The wider the operating temperature range, the more expensive the thermal imager.

Temperature measurement accuracy and speed

The accuracy of temperature measurements is calculated in laboratories using absolute black bodies, and usually the measurement error of thermal imagers does not exceed 2% of the result obtained. Usually by measurement speed we mean the inertia or response of the device. This is the time from the start of measurement during which you can get an accurate and self-sufficient result. As a rule, this time is much lower than for contact methods of temperature measurement. For high-precision instruments it is less than 0.2 seconds. High speed is important if you need to measure the temperature of a moving object, or an object that changes its state.

Thermal imager matrix size

The size of the matrix directly determines the clarity of a thermal photograph of an object, since the larger the size of the IR detector, the more sensitive elements perceive thermal radiation. Above we said that one pixel corresponds to one temperature value. It is clear that the higher the resolution of the matrix, the more temperature points can be tracked and, accordingly, a clearer picture is obtained. For example, the FLIR E30bx thermal imager with a 160x120 pixel matrix displays a thermal image of 19,200 pixels, and the FLIR E60bx thermal imager model, thanks to a larger 320x240 pixel matrix, displays 76,800 values. The higher the resolution, the better the image quality, and the more expensive the thermal imager itself is.

Important from the point of view of optics, but not so much as the resolution of the matrix, is the optical resolution. Optical resolution is actually the ratio of the distance from the device to the object to the diameter of the diagnostic spot. In terms of optical resolution, it is important that the entire object falls into the field of view. In fact, it determines from what distance you can take measurements of objects of a certain size. But at the same time, optical resolution does not in any way affect the image quality and the number of recorded temperature points. These indicators are determined by the resolution of the IR sensor matrix.

Temperature sensitivity of the thermal imager

When choosing a thermal imager, you should pay attention to such an indicator as temperature sensitivity. This indicator is also called the error when measuring temperature at two adjacent points. In fact, the lower the temperature sensitivity, the higher the quality of the picture seen on the screen. The lower the difference between the temperature of two neighboring points, the clearer the picture. Thermal imagers for hunting have a thermal sensitivity of 0.02 degrees and below. This allows you to distinguish between almost all objects that are at the same temperatures, even at night. In production, the low temperature sensitivity of thermal imagers helps not only to localize a thermal anomaly but also to determine its shape with high accuracy.

Thermal imager information display mode

When choosing a thermal imager, you should also pay attention to the modes in which the device can operate. The more of them, the more functional the thermal imager is, but on the other hand, it is more expensive. The simplest models of FLIR thermal imagers have only one FULL IR mode. This mode is nothing more than a full-screen thermal image. More complex thermal imagers also have additional modes that can increase measurement accuracy and, on the other hand, increase efficiency. For example, the Picture in picture mode is when an IR image is placed in a photographic image. This mode makes it easier to localize problem areas. Alpha Blending mode allows you to merge the visible image with the infrared. The highlight of the mode is the ability to select the ratio of two displays: from full visible to full infrared. This mode improves focus and details in the image. The IR/Visible Alarm mode allows you to separately display on the IR display areas with a given temperature, or with a given temperature range, the remaining areas are displayed in the visible range. And the last mode is the Full Visible Light mode of a simple digital camera. The most modern thermal imagers can operate in all of the listed modes, but their cost is much higher than conventional devices.

Functional equipment and components of the thermal imager

Before you settle on a particular device, you need to pay attention to its functional equipment and packaging. The scope of application depends on its equipment and configuration. Many thermal imagers have functions such as determining surface humidity and recording video in the infrared region of the spectrum. There are also devices that are equipped with zoom lenses, laser pointers and other devices. All this also affects both the specification and the final price.

So, when choosing a thermal imager, you need to very carefully pay attention to such characteristics as thermal sensitivity, operating temperature range, matrix resolution, and equipment. Choosing a thermal imager is an important step, which is why you need to clearly formulate the task and know what exactly is required. Flir thermal imagers are certified in the Russian Federation and come in a huge variety of models of various specifications: from thermal imagers for security before thermal imagers for hunting. You can choose exactly the device you need.

Pyrometers and thermal imagers are very effectively used to detect heat leaks in operating buildings or cold leaks in cooling systems. For builders, diagnostics using IR devices allows them to identify defects in the thermal insulation of a house, non-destructively determine the quality of the materials used, and, based on the data obtained, eliminate leaks, increasing the energy efficiency of the building. Considering that the output is accurate and systematized data (temperature values ​​are saved), it is possible to analyze the situation as a whole, determine the relevance of the problems and solve them one by one, starting with the more serious ones.

Thermal imagers and pyrometers are indispensable, for example, if you decide to purchase a house on the secondary market and have no idea how the thermal insulation of the enclosing structures was made. They very well clarify the situation with the technical condition of electrical installations: for example, an increased temperature of a conductor or circuit breaker indicates that it is overloaded, and if the connection heats up, it means that there is poor contact in that location. Also, IR devices help to identify errors in the implementation of thermal protection of stoves, boilers and fireplaces, show the thermal output of heating routes and places of leaks, the filling level of containers and reservoirs. Thermal scanners can easily detect waterlogging of building elements, damage to insulation, and colonies of pests.

So, the main purpose of a portable construction thermal imager/pyrometer is flaw detection, energy audit of enclosing structures and utilities.

How does a non-contact thermal detector work?

All objects that have a temperature higher than absolute zero emit infrared waves with a length of 0.74 to 1000 microns. This was stated in 1800 by the English scientist William Herschel, a famous solar researcher. It became clear that special radiation is emitted not only by hot metal or electrical discharges (everyone has seen this), but also by bodies with low temperatures, including below 0 ° C. IR rays are emitted by excited ions, and the wavelength changes with different heating of the object (the warmer the surface, the shorter the wave and the more intense the flow). A person can perceive this energy on the skin as heat, but does not see it.

It took time to learn to register infrared and thermal rays, recognize them and process the information received. In 1967, Wahl Instruments Inc. The first portable pyrometer was developed.

Both a pyrometer and a thermal imager are optical-electronic devices whose lenses capture invisible infrared radiation from objects and convert it into an electrical signal in the receiver, which is already processed into an easy-to-read type of indication (picture or numbers). The resulting electrical voltage is proportional to the power of the received radiation flux, so it is possible to obtain accurate digital temperature values ​​even in thermal photographs.

A thermal imager, like a digital camera, has a matrix, but each of its pixels shows not the color and brightness, but the temperature value at a specific point of the object under study. On the display, the user receives a raster image, where zones with different heating are displayed in certain colors, so you can very quickly get a general impression of the temperature situation in the diagnosed zone. Basically the device consists of:

• lens (made of germanium);
• an IR radiation receiver (most often based on a bolometer - a resistor that changes resistance depending on the power of the current flow);
• processing unit.

The pyrometer is an order of magnitude simpler in design and much cheaper; there is no thermogram or “photograph,” but the average surface temperature of the tested object is indicated in digital/text form.

Diagnostics with these devices is inexpensive and fast - according to the “point and shoot” principle. The highest temperature reading speed is available, within 0.15-0.5 seconds. Their range of action is limited only by the diameter of the working spot (it expands as it moves away) and the transparency of the air (smoke, dust, water vapor, carbon dioxide, ozone - reduce sensitivity). Data can be obtained from a few centimeters to several tens of meters.

Features of thermal imagers and pyrometers

To start choosing an IR detector, you should answer a few basic questions that will help you decide on the type of device, and then move on to considering specific models:

1. What material are the objects you will be testing made of?
2. What approximately will be the temperature of the diagnosed areas?
3. From what distance will measurements be taken?
4. In what environment will the device operate (ambient temperatures, transparency of the space between the device and the object...).

Spectral sensitivity (spectral range)

Note that different materials emit different wavelengths. For example, metal and glass reflect well, so they produce a short wave, while other materials produce a long wave. There is a concept of “surface blackness”, and there is a corresponding coefficient, which is significantly different for metals and for organic materials. The reality is that some pyrometers and thermal imagers do not read all wavelengths and cannot test all materials. They have a narrow specialization, as they are designed for a specific range, to work with specific materials. But there are also wide-spectrum universal devices that are suitable for most construction diagnostic conditions. The wavelength they pick up is usually in the range of 6-14 microns, for example, MicroRay RIDGID IR-100 or ADA TemPro 1600. Manufacturers almost always indicate this parameter in their data sheets.

MicroRay RIDGID IR-100

Temperature range

A pyrometer and thermal imager can perceive temperatures in a wide range: from -50 to +3000 degrees, sometimes they are “sharpened” for low temperatures (including sub-zero), and sometimes only for heated bodies. To get the most accurate results, you should choose a device that has the narrowest range. There is no point in purchasing a thermal detector that measures far beyond a thousand degrees if our task is to diagnose a home - even a household Bosch PTD 1 (from -20 to +200) is quite enough, but to monitor a fleet of electric motors you will need something else - say, DeWalt DCT 414 S1 (-30 to +550). The main thing is to follow the golden rule: “the temperature range should overlap the temperature of the object by 25%. It should be noted that the larger the range of measured temperatures, the more expensive the device is. Some advanced models have replaceable frequency filters, which makes it possible to adjust the device to a wider temperature range.

DeWalt DCT 414 S1

Temperature data error (measurement accuracy)

This parameter is always indicated by the manufacturers of the pyrometer or thermal imager; it is calculated in laboratory conditions on absolutely black bodies and, first of all, depends on the method of information processing; however, realities (in particular, the transparency of the environment and the correctness of user actions) make their own adjustments. Most portable thermal scanners provide an error within 2 percent of the results obtained.

Measuring speed

This characteristic of a pyrometer is also called “inertia”, “response time”. The performance of these devices is incomparable with the performance of contact devices for temperature diagnostics. Indicators of 0.25-0.5 seconds are considered normal (X-Line pIRo-850M - 0.5 s), thermal scanners with inertia within 0.15 seconds are fast, however, this is more important for testing moving objects or changing your physical condition.

Optical resolution

The second name for the most important property of pyrometers and thermal imagers is “sighting index”; it directly depends on the optics of the device. Optical resolution shows the ratio of the distance from the device to the test surface to the diameter of the diagnostic spot (it is its average temperature that is being studied). In this case, it is necessary to select a pyrometer in accordance with the size of the object being examined, since the basic diagnostic rule states that the object must completely fall within the working field of the detector and cover it so that foreign bodies with their “temperatures” do not get there. In other words: a specific sighting indicator determines from what distance it is possible to measure objects of a certain size; at the same time, this characteristic of the device determines the minimum size of the recorded thermal anomaly. Optical resolution with a ratio of 10:1 to 40:1 is considered universal; for working at long distances, devices with a viewing ratio of 100:1 and higher will be required.

In order not to tie the user to specific distances, variable focus (zoom) is used, and focusing can be manual or automatic. Interchangeable lenses are also used to work in different conditions.

Temperature sensitivity threshold (NETD characteristic)

The thermal sensitivity indicator of a thermal imager displays possible errors when testing the temperature at two adjacent points. This is a characteristic of the matrix that determines how small the recorded temperature difference between the object and its background can be. The normal indicator is 0.1 degrees at +30 °C (sometimes manufacturers indicate in Kelvin), but many devices work in an order of magnitude more detailed, which makes it possible to very accurately determine not only the presence, but also the form of a temperature anomaly, and, accordingly, the cause of its occurrence. For example, the Testo 881 thermal imager has a sensitivity rating of 0.05 degrees.

Testo 881

Automatic measurement compensation

The accuracy of diagnostics largely depends on external factors, and manually setting up the device can be quite difficult, so many modern thermal imagers can compensate for some negative aspects in automatic mode. For example, the reflectivity of an object’s surface (“blackness coefficient”) can be adjusted - from 0.2 to 1 (in steps of 0.1). Ambient temperature and air humidity can be detected and compensated for. Meanwhile, some cheap devices sometimes do not even have manual settings to take these factors into account.

Guidance system (sight)

Visual targeting helps control the thermal imaging area. In principle, guidance can be optical or laser. Optics help to diagnose at long distances, test very hot objects (from 1200 degrees), or if the beam is simply not visible in strong natural light. Laser sights can be “dot”, “double beam”, “circle”, and several options can be used in one device to choose from. “Point” and “double” are aimed at an object from a distance of 2-3 tens of meters, and “circle” is convenient for close testing (up to 7 meters). The “double” sight also forms a point in the right place, but here it is the intersection of two laser beams. A sight in the form of a circle is good because it shows the contours of the thermal scanner’s working spot. Most modern thermal imagers and pyrometers use a second class safe laser - red light.

Bosch PTD 1

Remote thermal scanner display

Matrix size (IR detector size) - this indicator applies only to thermal imagers. The size of the matrix determines the number of sensitive elements (elementary bolometers) and, accordingly, the available image clarity. An important characteristic of a thermal scanner (how much surface area per pixel) follows from this indicator - “spatial resolution”, or “field of view”. As we have already said, each pixel on the display is a reflection of the measured temperature at a specific point in the tested zone. The better the resolution, the finer details can be distinguished in the thermogram and conclusions can be drawn about the causes of temperature anomalies. For example, a device with a detector of 160x120 pixels measures 19,200 points, while a matrix with dimensions of 320x240 pixels (Testo 882) already diagnoses 76,800 points.

Testo 882

Some thermal imagers are equipped with a touch screen, which does not affect the technical characteristics of the device.

Pyrometer display. In pyrometers, digital or text information is displayed on the LCD screen, which can be located in one or several lines (Ryobi RP4030). Almost all pyrometers have a backlit display, which allows measurements to be taken in dark rooms.

Ryobi RP4030

Interchangeable, additional lenses

By changing the lens, the user can significantly diversify the functionality of the thermal imager. Telescopic optics allows you to zoom in/out of the shooting area and thus test small objects at a great distance. If you need to examine a large, extended object, you can use a wide-angle lens and get a panoramic image. It is worth noting that the wider the angle of view of the lens, the shorter the working distance will be, and vice versa.

terms of Use

When choosing a pyrometer or thermal imager, it is very important to pay attention to the ambient temperature at which the device can be used and at what humidity. Manufacturers do not hide this information, but do not confuse it with storage conditions - there is a wider range. Some cheap devices are limited in this regard and are designed for indoor operation (temperature from 0 to +40 degrees, humidity up to 80%). More universal thermal scanners operate outdoors, at sub-zero temperatures and humidity up to 90%. When comparing several models, take a look at the IP protection class of the housing; the average is IP54.

Signaling

This function allows you to set the maximum or minimum temperature, when detected, a sound signal is automatically heard or a light indication is activated. This way the user will not miss critical temperature changes and will react to the problem in time (Fluke Ti25).

Fluke Ti25

Onboard memory

Measurements are stored in both pyrometers and thermal imagers. This can be short-term storage of fresh data until the next measurement, as well as recording on built-in and removable media (various memory cards). Expensive thermal imagers can record voice comments and save diagnostic data as video footage (in IR mode or in the visible range).

Various information display modes

A modern thermal imager, in addition to the “full IR” mode, is capable of taking a regular digital photograph or regular video recording with a high frame update rate (more than 40 Hz). The visible image can be superimposed on the infrared image, thus facilitating the identification of the defective area. In some devices, you can set extreme temperatures at which only areas that are off-scale in temperature will be displayed on a visible photograph in IR mode; you can simply set them to be highlighted on a fully infrared image (Flir InfraCAM). You can also display detected dew points and waterlogged areas on the display. For ease of orientation, a projection of a laser target designator is displayed on the screen. Sometimes thermal imagers have an isotherm function - a specified temperature range is depicted in a specific color.

Flir InfraCAM

Surface moisture detection

In manual mode, humidity and air temperature are entered, and the device itself will show problem areas in the tested area. Humidity can also be measured automatically, after connecting a special radio probe. An additional function is an alarm about the found dew point.

PC connection

Images obtained as a result of the study are available for viewing directly on the display. However, for analysis and reporting, for using the device as a recorder, the information is sent to a computer. The connection can be made via analogue or discrete outputs. The presence of a USB connector is considered good form, for example, Optris LaserSight (LS) and others. The software is usually included and updated free of charge, but sometimes it needs to be purchased separately.

Optris LaserSight

Work area lighting

Many pyrometers and thermal imagers have built-in LED lights that illuminate the object of study, so diagnostics are possible even in conditions of poor visibility.

Ergonomics, type of execution

Modern thermal imagers and pyrometers are used either stationary or portable. The former are used in production, are powered from the network and often have a narrow specialization, while the latter are more universal, characterized by low weight and modest dimensions.

Industrial thermal imagers and pyrometers are encased in a metal case; they are well protected from all kinds of influences (dust, vibration, humidity, chips, high temperature). As a rule, stationary instruments provide more accurate data.

Portable devices for infrared diagnostics can look like a camera or video camera, but most often they are made in the form of a pistol made of engineering plastic, where the trigger is used to start testing, and at the end of the body there is a control display with menu control buttons. Their weight rarely exceeds 500 g, many specimens are lighter than 200 grams (ADA TemPro 900 - 170 grams). The well-designed device can be held and operated with one hand. High-quality devices are protected from falling from a height of 2 meters (Fluke TiR1), at least the manufacturer confidently claims this.

Fluke TiR1

Power Options for Infrared Thermal Scanners

Stationary devices are powered from the network through step-down devices. Portable thermal detectors are usually powered by alkaline batteries (AA, Krona, AAA, “tablet”). Many manufacturers supply their thermal scanners with various batteries (nickel-cadmium and lithium-ion); by the way, you can also connect power via a USB port. Those who create power tools and have complete battery systems at their disposal install batteries from power units on their pyrometers and thermal imagers. For example, the DeWalt DCT 414 S1 and model S1 DCT416S1 are equipped with a 12-volt unit with a capacity of 1.5 Ah. Milwaukee has gone a little further and sells its thermal imager and pyrometer without a battery or charger. A consumer who already has a mobile tool from this company can save a lot of money by installing an M12 system battery on the diagnostic tool.

DeWalt S1 DCT416S1

Selecting the technical and functional characteristics suitable for your conditions, as well as the successful configuration of a thermal scanner, is certainly an important task, but you should also pay attention to metrological support from the manufacturer so that the results of the energy audit (if necessary) can be legalized in the appropriate authorities. The device must undergo standardization! Considering the technical complexity and high cost of these measuring devices, we recommend that you be sensitive to issues of warranty and service.

Price

A pyrometer, unlike a thermal imager, is a simpler and relatively inexpensive device. Entry-level models can be purchased for approximately 2,500 rubles, for example, ADA TemPro 300 with a temperature range from -32 to +350 degrees, or the Laserliner ThermoSpot, which has similar characteristics. With the expansion of the range, the cost increases almost proportionally (the price tag for the ADA TemPro 1200, capable of measuring up to 1200 degrees, is 9,500 thousand). It is difficult to see other pricing patterns - manufacturers act at their own discretion, offering different sets of additional options. Note that devices from companies that create power tools have good technical and performance characteristics at a moderate cost (DeWalt DCT 414 S1 - 5000, Ryobi RP4030 - 3500, Bosch PTD 1 - about 4500 rubles).

With thermal imagers (for construction purposes), the situation is more complicated. In these devices, in addition to the fundamental operating features (90% of the price is determined by the characteristics of the matrix and optics), it is necessary to take into account a huge number of additional functions that make the user’s life easier. Do not forget about the breadth of the basic delivery package and the “promotion” of the brand. Few thermal imagers cost about 30,000 rubles; these are budget models, for example, Fluke VT04 and model VT02, as well as DeWalt DCT416S1. The price tag for the FLIR i3 device is slightly higher than the minimum - about 43,000. Thermal imagers costing about 100,000 rubles (Testo 875-1 or Fluke TiS) can be considered middling. There are models for 250,000 (Testo 875-2) and 430,000 rubles (FLIR T335). For reference, a purely professional FLIR P640 costs over one and a half million.

The estimated cost of conducting an energy audit (survey + report) of a private house by specialized organizations is from 50 rubles per square meter of building. As a rule, they charge at least 10,000 for a one-story building. A thermal imager can be rented; a day of using an average device in terms of characteristics will cost you about 2-3 thousand rubles; naturally, you need to leave about 20-40 thousand as a deposit. You can save a little if you rent a simpler model and for a long period of time, for example, teaming up with someone.

Hello.

A thermal imager is an extremely useful thing for anyone who likes to do something with their own hands, study something, etc. But for many years they were unaffordable. Fortunately, progress is gradually correcting this situation.

A few months ago, I compared the inexpensive Fluke VT04, FLIR TG165, and FLIR C2 prototype thermal imagers. Then I tested the serial FLIR C2 a little. Well, now I thought: why haven’t I written about this on Geektimes yet?..

In principle, I immediately posted all the test results on YouTube, so those who are too lazy to read can watch the video. But I warn you, it’s a total of 40-45 minutes. For those who are more interested in the text, this article is for you. For those who are bored by all this - for those there are cats at the end of the article.

The article is based on the video, so it is divided exactly according to them into the following parts:
1 - general overview;
2 - technical characteristics;
3 - test, examination of electronics;
4 - test, inspection of electrical equipment;
5 - measurement accuracy test;
6 - test, inspection of the premises.

So, point 1: general overview.

For starters, prices, since the title says “inexpensive.” I took the prices at the time of writing from the first seller I came across who had all three models. Perhaps something can be bought cheaper. Interestingly, the prices turned out to be the same as a few months ago...

So:
- Fluke VT04 - 35,000 rubles;
- FLIR TG165 - 40,000 rubles;
- FLIR C2 - 64,000 rubles.
There in USA, VT04 is $500, TG165 is $500, and C2 is $700.

Now let's take it in our hands.

The Fluke VT04 is a total disappointment. I have nothing against Fluke at all, I have their thermal imager at work and it was purchased on my recommendation. But in this case, one gets the feeling that its body and ergonomics were designed with the goal of pushing the buyer to buy something more expensive...

Its handle is very wide and uncomfortable. Although basically everything is covered with rubber, you grab hard, unpleasant plastic with your hand, and the transition from bare plastic to covered with rubber is a very large step that puts pressure on your fingers.

The VT04 shutter release button is simply a creation of Satan... It is narrow, slippery and requires a lot of effort to take a picture, and is also located at such an angle that the finger slips and presses on it with the very edge. As a result, when actively using the device, your index finger really starts to hurt!

The body panels fit poorly: where is the gap, where the rubber coating rises from compression.
The SD card is not covered with anything; during active use, it can easily get caught on something and break. Plus, it is held together only by friction, so you can also lose it...

FLIR TG165 after that is just heaven and earth...
The body is completely rubberized, all panels fit perfectly, the handle is extremely convenient in shape and size, and the release button is also “for people.” And, of course, the SD card is held on with a latch and covered with a rubber plug, so nothing will happen to it under any circumstances. In addition, the TG165 is noticeably more compact.

FLIR C2 is something completely different... It is made in the form factor... of a smartphone!
Probably for those who are used to shooting with a smartphone, it will be extremely convenient. But it was, at least, unusual for me: I’m used to shooting with cameras, or, in extreme cases, with thermal imaging pistols, and I don’t have a smartphone at all. In my opinion, it would be worth changing the shape of the case a little so that the C2 could be held as a point-and-shoot camera. But, alas, they made it in such a way that it’s only like a smartphone, otherwise you either press the touchscreen for the wrong reasons, or block the lens, or you can’t reach the shutter button.

But the build quality is difficult to undermine even in a prototype, and the production model turned out to be completely ideal.

Point 2: technical specifications.

It’s worth starting with the fact that the Fluke VT04 is not positioned as a thermal imager at all, but as a “visual infrared thermometer.” What does this involve from a technical point of view? The fact is that in conventional thermal imagers there is a matrix called a microbolometer, consisting of thermistors, but here a matrix of pyroelectric elements is installed. Pyroelectric sensors are typical for infrared thermometers (pyrometers), but there is only one sensor. They immediately made a matrix of 31x31 sensors, which made it possible to obtain some kind of thermal image.

To compensate for the very low resolution, the device received a relatively small viewing angle of 28°x28° and a visible camera, whose image is mixed with thermal in different ratios, depending on the wishes of the user. We can first find a warm/cold spot in the pure IR range, and then gradually move on to the visible image and understand exactly which real object it corresponds to. By saving the image in Fluke's own format, you can then change the blending factor on your computer. In the alternative BMP, of course, there is no such option, just a conditional screenshot. By the way, he retains this BMP for a very long time...

The big disadvantage of VT04 was the temperature measurement not based on the central pixel of the matrix (and ideally, any pixel of your choice), which would be logical, since the number of pixels is odd, but averaged over a square of 7x7 pixels. Taking into account the low resolution of the matrix, we get a very large area; the temperature of a small object cannot be accurately measured:

Gray corners show the averaging area. As you can see, the temperature turned out to be noticeably lower than what you would expect from your finger... By the way, not as much lower as one might expect, taking into account averaging over such an area. But more on this in paragraph 5.

Saving the image in Fluke’s own format does not change anything: on the computer you can still only see the average temperature of the large square in the center. Most likely this is due to the very high noise of the matrix, which is several times greater than that of a microbolometer.

But, of course, it cannot be said that the device has only disadvantages. There is also a serious plus!
You can put it on a tripod and set up automatic shooting. Either interval or when the critical temperature is exceeded. So for the task of long-term observation of a static object, it may be the best choice.

The FLIR TG165 is also positioned not as a thermal imager, but as a “thermal imaging infrared thermometer.” But the technical side here is completely different from Fluke. It creates a thermal image using a conventional FLIR Lepton thermal imaging module with a microbolometer with a resolution of 80x60 pixels. But to save money, this microbolometer is not calibrated and does not measure temperature! Instead, the device has a separate pyrometer built into it, which measures the temperature approximately in the center of the thermal imager's view. To more accurately determine the measurement area, a double laser pointer is built in, which shows not only the location itself (the middle of the segment connecting two points from the lasers), but also the diameter of the averaging area (the distance between the points). By the way, this diameter is three times smaller than the side of the square over which the VT04 averages the temperature, so small objects are measured much more accurately:

Please note that there is a larger viewing angle (50°x38°) and much less noise.
However, the functionality of the device is absolutely minimal: only show a thermal image, measure the temperature at one point and save “screenshots” of the screen in BMP. But in the vast majority of cases, nothing else is needed! So, in my opinion, for most people this model will be optimal.

Here FLIR C2 is already a thermal imager without any reservations. Also a FLIR Lepton module with a microbolometer with a resolution of 80x60 pixels, but already calibrated, we measure the temperature directly from the image. By saving the image in the only possible “radiometric JPEG” (JPEG screenshot with attached data from the microbolometer ADC and the source image from the visible camera) and opening it with a special program (downloadable for free from the FLIR website), we can find out the temperature of any point, look at temperature distributions, etc. .

Alas, Lepton fundamentally does not understand temperatures above 150°C... If TG165, for example, measures from -25°C to +380°C, then here we only have from -20°C to +150°C. In most cases it will be enough, but not always.

Another minus is the battery life. Only two hours are guaranteed. The two previous devices work at least eight.

But then a huge plus is FLIR MSX technology. It can be understood most clearly from this short video:

Contours are identified in the visible camera image and then added to the thermal image, dramatically increasing detail. I have not seen anything better in terms of combining thermal and visible images. Moreover, MSX leads by a huge margin, simultaneously providing maximum information from both ranges.

Plus, the viewing angle here, in my opinion, is closer to optimal: 41°x31°.
Finally, and very pleasingly, the C2 can be connected to a computer and it is recognized as a webcam, transmitting an image in real time.

Point 3: test, examination of electronics.

An open system unit serves as a test object.

Fluke VT04 shows that it copes with such work quite well.

But there are a number of difficulties:
- the combination of visible and thermal images is not accurate due to parallax;
- we have to constantly switch the modes of mixing visible and thermal images to understand what is heating up there;
- frames are saved for a very long time, if there is a task to later show someone else what they saw, then this greatly slows down the work;
- the matrix is ​​“braking”, the picture can actually become blurred during fast movements;
- you have to “scan” for quite a long time due to the not very wide viewing angle, there is a risk of missing something;
- as mentioned above, the temperature of small objects cannot be accurately measured.

The FLIR TG165 does a noticeably better job. Although it does not have an additional visible camera, the relatively high resolution of the thermal image allows us to understand what we are looking at. A large viewing angle allows you to immediately inspect a large area. Well, in terms of measuring the temperature of small objects, it is much better. Although, of course, they cannot measure very small details.

Finally, the FLIR C2. Unfortunately, it still performs worse than the VT04 when it comes to combining thermal and visible images at close distances. At a distance of less than 1 m, it is not designed in this regard. You have to turn off MSX, otherwise it just gets in the way. Moreover, this could be corrected in software, expanding the range of parallax compensation to short distances, but this was not in either the prototype or the production model.

Nevertheless, C2 still copes with this job better than TG165: in addition to all the advantages of the 165, it can also measure the temperature of the smallest parts on the board.

Point 4: test, inspection of electrical equipment.

In general, the results are the same as in the previous test.
But there is an important difference: due to the increased distance (there is somehow no desire to climb closely under 380 volts), FLIR C2 here already works quite well with MSX. I think its significance will be clear in the pictures below. I was especially pleased with the backlight built into the device, which allows you to work as efficiently as possible even in a dark room. Fluke's visible camera became noticeably less effective due to poor lighting.

About the TG165, we can say that the laser here has become useful not only as an indicator of the measurement area, but also as an indicator of what we are looking at (let me remind you that the measurement area approximately coincides with the center of the image). Helps in the absence of a visible range camera. At short distances, due to the same parallax, this did not work.

Point 5: Measurement accuracy test.

Initially, my plans did not include such a test. But somehow I turned on VT04, pointed it at the wall and saw this on the screen:

And somehow I can’t believe that it’s +30 in my apartment...

The instructions for the device say that after turning it on, it needs 5-10 minutes to warm up in order to give accurate readings. And indeed, gradually his readings began to decrease... But even after half an hour of work, he did not want to show less than 26°C on this wall. But I didn’t want to believe in such a temperature in the apartment: all the other temperature meters (including TG165 and C2) found at home spoke about 23-24°C.

But this is not an indicator yet... You need something with a known temperature and emissivity. Water with melting ice was chosen as such a test object. Its emissivity is obviously 0.96, and its temperature is simply by definition equal to 0°C. The thermocouple of my multimeter only confirmed that the determination was being made.

After waiting 5-10 minutes after turning on, we check the Fluke VT04 on the countertop, and then on test water:

As we can see, he consistently overestimates the readings. Moreover, it seems that the higher the temperature, the stronger it is.
Now FLIR TG165:

Simply gorgeous! It is difficult to expect any more accuracy than this from an infrared temperature meter. It's just a standard device. Once again I can recommend everyone to take the TG165.
Finally C2:

Hmm... Please note: at room temperature it shows exactly what is needed, but when it comes to cold it seriously underestimates. However, here I have a prototype, what will happen in the production model? A few weeks later I found out:

It’s already better, it fits the standard, but it’s still not ideal.

I have an assumption that because. heating is easier than cooling; cheap matrices are calibrated only from room temperature and above, and below room temperature - extrapolation. In the prototype, the extrapolation algorithm was poorly developed, so the readings were completely underestimated, but in the production model they have already corrected it, it began to fit into the standards, but nothing more. However, I repeat that this is just my guess.

Point 6: test, inspection of the premises.

Again, the same thing can be said as in points 3 and 4.
Fluke VT04 copes with the task, it is quite possible to work.

But there are a lot of shortcomings, especially the low resolution with a small viewing angle.
FLIR TG165 works much better.

The image is much more detailed, the viewing angle is much wider - that's what you need. You can't really dig into it.
But FLIR C2 is still ahead at the expense of MSX.

And finally, the promised cats:

In order to identify thermal anomalies in buildings and industrial facilities, their energy inspection is carried out. To perform an energy audit, special devices that work with thermal radiation are used - thermal imagers. They allow you to reproduce a thermographic image of the building or object under study. The pictures make it possible to accurately identify problem areas in heating systems, as well as points through which heat waves leak in door and window openings. In order for a thermal imager to clearly perform its assigned functions for energy inspection and fully justify the money spent, when choosing a model, it is necessary to pay attention to the main characteristics that determine the scope of its use.

Infrared Detector Size

This parameter affects the quality of the image obtained on the screen. To clearly display the situation with thermal radiation at an object and accurately determine temperature values, devices with a matrix size of at least 320 × 240 pixels are better suited. It allows you to measure a large number of temperature values. A high-quality picture makes it easier to determine the location of a heat leak or other anomaly. The higher the resolution, the clearer the picture will be from a distance. However, this parameter should not be confused with screen resolution, which will not affect image improvement if the detector size is insufficient.

Maximum measurement limit

To conduct a study of heat loss in buildings, as well as houses and cottages, it is not necessary to measure high temperatures. Therefore, it is enough to purchase a thermal imager with a measurement limit of up to 250ºС. If the product is purchased for energy audits of industrial, metallurgical and explosive facilities associated with heat treatment, models are required that have higher maximum limit values: from 600 ºС to 2000 ºС.

Device operating range

Depending on the conditions in which you plan to shoot, when choosing a product, you must take into account the temperature range recommended by the manufacturer for using the thermal imager and guaranteeing its proper operation. If the work is planned to be carried out only indoors, then a temperature range from 0ºС to +40ºС is sufficient. If outdoor research is necessary, it is recommended to pay attention to devices that provide shooting at −20ºС - +50ºС. The permissible air humidity can correspond to a value of 95%.

When performing complex work on energy audits of buildings or industrial facilities, it is very important that even the smallest temperature differences are displayed on the screen. Such measurements will be provided by thermal imagers with a matrix whose sensitivity is 0.05 degrees. Thanks to such devices, it is possible not only to determine defective points (locations) of heat leakage, but also to determine the cause of the anomaly by the form of radiation.

Display Modes

Thermal imagers also differ in image reproduction modes. In addition to the main one - “full IR”, which is present in all models, some devices also have additional modes that allow you to focus on a specific point and magnify the image for image detail. Thanks to this functionality, it is possible to identify problem areas with great accuracy.

Additional functions

Among the additional features, it is recommended to pay attention to the function of overlaying an infrared image on a visible image. Many products are equipped with internal storage devices. This option is in demand when there is a need to register the information received. Cheaper models have a special output for connecting any external storage device. For a professional energy audit, the device must have the ability to enter emissivity values, as well as reflected temperature. These parameters ensure high measurement accuracy.

The presence of special software will allow you to connect the device to a computer to transfer information. It is desirable that it be saved in JPEG format, since in this case the data can be sent via Bluetooth, Wi-Fi or, if necessary, via the built-in USB port. The presence of a built-in digital camera will allow you to document information for the purpose of later using it to compile energy audit reports. But, before buying a thermal imager, you need to understand exactly and also make sure that such functions are in demand, because they significantly increase the cost of the models.

General requirements for devices

When choosing thermal imagers for inspecting buildings and structures, it is also necessary to take into account that they must meet the following requirements:

• When measuring electrical circuits, do not create electromagnetic interference.
• Have a sealed housing that is well protected from dust and moisture.
• Be portable and ergonomic, therefore, for ease of use, it is recommended to choose devices weighing no more than 15 kg.
• Autonomous operation from the built-in power source should be ensured for at least 2-4 hours, and it should also be possible to replace batteries in the field.

For each device, it is necessary to check the calibration certificate as a guarantee of accurate results during an energy audit.

Among the popular manufacturers of thermal imagers for energy inspection of buildings, explosive and industrial facilities are Flir, Fluke, Testo. With extensive experience, they produce devices that are reliable and easy to use, and also allow for high-precision surveying.