- How a non-contact thermal detector works
- Features of thermal imagers and pyrometers
- Spectral sensitivity (spectral range)
- Measured temperature range
- Temperature data error (measurement accuracy)
- Measurement speed
- Optical resolution
- Temperature sensitivity threshold (NETD characteristic)
- Autocompensation of measurements
- Guidance system (sight)
- Remote Thermal Scanner Display
- Interchangeable, optional lenses
- Onboard memory
- Various display modes
- Surface moisture detection
- PC communication
- Illumination of the working area
- Ergonomics, type of execution
- Infrared Thermal Scanner Power Options
- The cost
Pyrometers and thermal imagers are very effectively used to detect heat leaks in existing buildings, or cold leaks in cooling systems. For builders, diagnostics using infrared devices allows you 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 at the output we have accurate and systematized data (temperature values are saved), it is possible to analyze the situation as a whole, determine the degree of urgency of the problems and solve them in turn, starting with more serious.
Thermal imagers and pyrometers are irreplaceable, for example, if you decide to buy a house on the secondary market and have no idea how the enclosing structures were insulated. They very well clarify the situation with the technical condition of electrical installations: for example, an increased temperature of a conductor or a circuit breaker indicates that it is overloaded, and if the connection heats up, it means that there is poor contact in this place. Also, infrared devices help to identify errors in the implementation of thermal protection of stoves, boilers and fireplaces, show the heat output of heating routes and places of leaks, the level of filling of tanks and reservoirs. Thermal scanners can easily detect waterlogging of building elements, damage to insulation, colonies of colonized pests.
So, the main purpose of a portable building thermal imager / pyrometer is flaw detection, energy audit of enclosing structures and utilities..
How a non-contact thermal detector works
All objects that have a temperature higher than absolute zero emit infrared wavelengths from 0.74 to 1000 microns. This was stated in 1800 by the English scientist William Herschel, the famous explorer of the Sun. It became clear that special radiation is emitted not only by a red-hot metal or electrical discharges (everyone saw this), but also by bodies with a low temperature, including below 0 ° C. Infrared 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 as warmth with his skin, but does not see it..
It took time to learn how to register infrared, heat 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 optoelectronic devices that capture invisible infrared radiation from objects with lenses and convert it into an electrical signal in the receiver, and it 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, therefore it is possible to obtain accurate digital temperature values even on thermal photographs.
A thermal imager, like a digital camera, has a matrix, but each of its pixels does not show 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 from germanium);
- an infrared radiation receiver (most often based on a bolometer – a resistor that changes its 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, “photograph”, but the average surface temperature of the tested object is indicated in digital / text form.
Diagnostics with these devices is inexpensive and quick – according to the “point – shoot” principle. The fastest temperature readout speed is available, within 0.15-0.5 seconds. The range of their action is limited only by the diameter of the working spot (it expands when removed) and the transparency of the air environment (smoke, dust, water vapor, carbon dioxide, ozone – reduce the sensitivity). Data can be obtained both from a few centimeters and from 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 determine the type of device, and then proceed to consider specific models:
- What material are the objects that you will test made of??
- What is the approximate temperature of the diagnosed areas?
- From what distance will the measurements be made?
- In what environment will the device work (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 give out a short wave, while other materials – a long one. There is a concept of “surface blackness”, and there is a corresponding coefficient, which is several times different for metals and for organic materials. The reality is that some pyrometers and thermal imagers do not read all waves 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 broad-spectrum universal devices that are suitable for most conditions of construction diagnostics. The wavelengths that they capture are 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 passports.
MicroRay RIDGID IR-100
Measured temperature range
The pyrometer and thermal imager can perceive temperature in a wide range: from -50 to +3000 degrees, sometimes they are “sharpened” for low values (including minus ones), and sometimes only for heated bodies. For the most accurate results, select the device that has the narrowest range. It makes no sense to purchase 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, something else will be required – for example, DeWalt DCT 414 S1 (-30 to +550). The main thing is to observe 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, the realities (in particular, the transparency of the environment and the correctness of the user’s actions) make their own adjustments. Most portable thermal scanners are accurate to within 2 percent of their results..
This characteristic of the 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), thermoscanners with inertia within 0.15 seconds are high-speed, however, this is more important for testing moving objects, or changing your physical condition.
The second name of 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 tested surface to the diameter of the diagnostic spot (it is its average temperature that is investigated). In this case, it is necessary to choose a pyrometer in accordance with the size of the object being examined, since the basic diagnostic rule states that the object must completely fall into the working field of the detector and overlap it so that foreign bodies with their “temperatures” do not get there. In other words: a specific sighting indicator determines the distance from which 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 long distances, devices with a sighting ratio of 100: 1 and higher are required.
In order not to tie the user to specific distances, a variable focus (zoom) is applied, while focusing can be manual or automatic. Also, interchangeable lenses are used to work in various conditions..
Temperature sensitivity threshold (NETD characteristic)
The thermal sensitivity indicator of the thermal imager displays possible errors when testing the temperature at two adjacent points. This is a characteristic of the matrix, which determines how small the recorded difference between the temperature of 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 an order of magnitude more detailed, which allows you to very accurately determine not only the presence, but also the shape of the temperature anomaly, and, accordingly, the cause of its occurrence. So, for example, the Testo 881 thermal imager has a sensitivity index of 0.05 degrees.
Autocompensation of measurements
The accuracy of diagnostics largely depends on external factors, and it can be quite difficult to manually configure the device, therefore, many modern thermal imagers in automatic mode can compensate for some negative moments. For example, the reflectivity of the object’s surface (“emissivity”) can be corrected – from 0.2 to 1 (in increments of 0.1). Ambient temperature and air humidity can be detected and compensated. Meanwhile, some cheap devices sometimes do not even have manual settings to take these factors into account..
Guidance system (sight)
Visual aiming helps control the thermal imaging area. In principle, guidance can be optical and 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 come in “point”, “double beams”, “circles”, and in one device several options can be used to choose from. “Point” and “double” are aimed at the object from a distance of 2-3 tens of meters, and the “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. The sight in the form of a circle is good because it shows the contours of the working spot of the thermal scanner. Most modern thermal imagers and pyrometers use a safe second class laser – red glow.
Bosch PTD 1
Remote Thermal Scanner Display
Matrix size (size of the IR detector) – 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. This indicator implies an important characteristic of a thermal scanner (what is the surface area per pixel) – “spatial resolution”, or “field of view”. As we already said, each pixel on the display is a display of the measured temperature at a specific point in the tested zone. The better the resolution, the finer details can be distinguished on the thermogram and conclusions can be drawn about the causes of temperature anomalies. For example, a device with a 160×120 pixel detector measures 19,200 points, while a matrix with dimensions of 320×240 pixels (Testo 882) already diagnoses 76800 points.
Some thermal imagers are equipped with a touchscreen display, 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 in dark rooms.
Interchangeable, optional lenses
By changing the lens, the user can significantly diversify the functionality of the thermal imager. Telescopic optics allow you to zoom in / out the shooting area and thus test small objects at a great distance. If you need to explore a large, extended object, you can use a wide-angle lens and get a panoramic picture. It is worth noting that the wider the angle of “view” of the lens, the shorter the working distance will be, and vice versa.
When choosing a pyrometer or thermal imager, it is very important to pay attention to what ambient temperature the device can be used at 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 use (temperature from 0 to +40 degrees, humidity up to 80%). More versatile thermal scanners operate outdoors, at subzero temperatures and humidity up to 90%. Comparing several models, take a look at the IP rating of the housing, the average is IP54.
This function allows you to set the maximum or minimum temperature indicator, upon detection of which a beep is automatically emitted or a light indication is triggered. This way the user will not miss critical temperature changes and will react to the problem in time (Fluke Ti25).
Memorization of measurements is performed both in pyrometers and in thermal imagers. This can be a short-term storage of fresh data until the next measurement, as well as writing to built-in and removable media (various memory cards). Expensive thermal imagers can record voice comments, save diagnostic data as video (in IR mode, or in the visible range).
Various display modes
A modern thermal imager, in addition to the “full IR” mode, is capable of making a regular digital photograph, or a regular video recording with a high frame refresh rate (over 40 Hz). The visible image can be superimposed on infrared, thus making it easier to identify the defective area. In some devices, you can set extreme temperatures at which only areas that are off scale in temperature will be displayed in the visible photo in the IR mode, you can simply set them to be selected in a fully infrared image (Flir InfraCAM). Also, the display can display the found dew points and waterlogged areas. For the convenience of orientation, the projection of the laser designator is displayed on the screen. Sometimes the isotherm function is available in thermal imagers – a specified temperature range is displayed in a specific color.
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 in automatic mode after connecting a special radio probe. An additional function is an alarm about the found dew point.
The images obtained as a result of the examination 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 analog or digital outputs. The presence of a USB connector is considered a good form, for example, Optris LaserSight (LS) and others. The software is usually included in the package and is updated for free, but sometimes you need to buy it separately.
Illumination of the working area
Many pyrometers and thermal imagers have built-in LED lights that illuminate the object of study, so diagnostics is possible even in poor visibility..
Ergonomics, type of execution
Modern thermal imagers and pyrometers are used either permanently or as portable. The former are used in production, are powered from the network and often have a narrow specialization, and the latter are more versatile, differ in their small weight and modest dimensions..
Industrial thermal imagers and pyrometers are clad in a metal case, they are well protected from all kinds of influences (dust, vibration, humidity, chips, high temperature). Typically, stationary instruments provide more accurate data..
Portable devices for infrared diagnostics may look like a camera or video camera, but most often they are made in the form of a pistol made of structural plastic, where the trigger is used to start testing, at the end of the case there is a control display with menu control buttons. Their weight rarely exceeds 500 g, many of them are lighter than 200 grams (ADA TemPro 900 – 170 grams). The well-designed apparatus is held and operated with one hand. Quality devices are protected from falling from a height of 2 meters (Fluke TiR1), at least, the manufacturer confidently states this.
Infrared Thermal Scanner Power Options
Stationary devices are powered from the network through step-down devices. Portable thermal detectors are usually powered by alkaline batteries (AA, CZK, AAA, “pills”). Many manufacturers supply their thermal scanners with various rechargeable batteries (nickel-cadmium and lithium-ion), by the way, you can also connect power via the USB port. Those of them who are engaged in the creation of power tools and have at their disposal complete battery systems, install batteries from power units on their pyrometers and thermal imagers. For example, DeWalt DCT 414 S1 and model S1 DCT416S1 are configured with a 12-volt unit with a capacity of 1.5 Ah. Milwaukee has gone a bit further and sells its thermal imager and pyrometer without a battery or charger. A consumer who already has a mobile tool of this company can save a lot by supplying an M12 system battery to the diagnostic tool..
DeWalt S1 DCT416S1
The choice of technical and functional characteristics that are 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 an energy audit (if necessary) can be legalized in the appropriate authorities. The device must be standardized! Considering the technical complexity and high cost of these measuring devices, we recommend that you be scrupulous about the issues of warranty and service..
A pyrometer, in contrast to a thermal imager, is a simpler and relatively inexpensive device. Entry-level models can be purchased for about 2,500 rubles, for example, the ADA TemPro 300 with a temperature range of -32 to +350 degrees, or a similar Laserliner ThermoSpot. 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 9500 thousand). Other pricing patterns are difficult to see – manufacturers act at their own discretion, offering different sets of additional options. Note that devices from companies that create power tools (DeWalt DCT 414 S1 – 5000, Ryobi RP4030 – 3500, Bosch PTD 1 – about 4500 rubles) have good technical and operational characteristics, at a moderate cost..
The situation with thermal imagers (for construction purposes) is more complicated. In these devices, in addition to fundamental operating features (90% of the price is formed from 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 set and the “promotion” of the brand. Few thermal imagers cost about 30,000 rubles, these are budget models, for example, the Fluke VT04 and model VT02, as well as the DeWalt DCT416S1. Slightly higher than the minimum price tag for the FLIR i3 device – about 43,000. Thermal imagers costing about 100,000 rubles (Testo 875-1 or Fluke TiS) can be considered average. There are models for 250,000 (Testo 875-2) and 430,000 rubles (FLIR T335). For reference, a purely professional FLIR P640 costs over 1.5 million.
The estimated cost of an energy audit (survey + report) of a private house by specialized organizations is from 50 rubles per square meter of the building. As a rule, they take at least 10,000 for a one-story building. A thermal imager can be rented, a day of using an average device will cost you about 2-3 thousand rubles, of course, you need to leave about 20-40 thousand as a deposit. You can save a little if you rent a model that is simpler and for a long time, for example, by teaming up with someone.