Absolute zero

Absolute zero is -273.15 ° C (0 K = -459.69 ° F). No object emits infrared energy at a temperature above absolute zero, in which case it means that they do not emit any infrared radiation.

Absorption / uptake

When the electromagnetic infrared radiation hits an object, the latter absorbs a certain amount of infrared energy. The absorption of infrared energy involves heating the object. Warmer objects emit more infrared radiation than objects of lower temperature. Absorption of infrared radiation emitted is converted into infrared radiation (coming from the object). The absorption coefficient, thus, corresponds to the ratio of the radiation. The incident infrared radiation, which is not absorbed by the object is reflected and / or missed (pass through the object).

Black body

An object that absorbs all the energy of the incident infrared radiation, converts it to its own infrared radiation and fully rejects him. Absolute emissivity of the radiator is unity. For this reason, there is no reflection or transmission of radiation. Objects having the properties of this kind does not exist in nature. Devices for the calibration of thermal imagers are called "black body". However, their emissivity less than one (? 0.95).

The time for temperature stabilization

The amount of time required for thermal adaptation to the ambient temperature at the site of measurement. Heat stabilized detectors of the same type as in the testo 880 has a relatively short time of stabilization (balancing) the temperature.

Hot / Cold Spot

The coldest point on the IR image is called a "cold spot", the hottest - the "hot spot". With the function "Auto Hot / Cold Spot," you can display imager these two points. This feature is also available in many software packages, such as Testo IRSoft 2.0. Through this software you can also display the hot and cold point of any selected area of ​​IR images.

Two-point measurement

2-point measurement is carried out through two crosshairs on the display of the thermal imager, with the aid of which the individual values ​​of the temperature reading.


The detector receives infrared radiation and converts it into an electrical signal. The size of the detector is specified in pixels.

The ideal emitter

See the "blackbody"

Gray body emitter

Almost all of the objects encountered in practice is called "gray bodies" or "real emitters." In contrast to the absolute black bodies, gray bodies would not absorb all incident infrared radiation on them. In this case, part of the incident light is always reflected and some is absorbed by the surface. Thus, the emissivity of a gray body radiator is always less than unity.


The lines connecting the points with the same temperature. You can display the isotherms using the software for analysis (for example, Testo IR Soft 2.0). In the course of the isotherms show that all points on the IR image with the values ​​of the temperature within the specified range are allocated the same color.

IR image

The image, which shows the temperature distribution on the surface of objects by using different colors for different temperatures. Infrared images are created using the thermal imager.

Infrared radiation

Infrared radiation is electromagnetic radiation of heat. All objects with temperatures above absolute zero (0 K = -273.15 ° C) emit infrared radiation. Infrared radiation covers the wavelength range from 0.75 mm to 1,000 mm (= 1 mm) and, thus, is bordered with a range of wavelengths of visible light (0.38 to 0.75 mm). Thermal imagers are usually measured by long-wave infrared radiation in the range from 8 mm to 14 mm (eg, testo 880), as atmosphere in the long-range good passes infrared light.

IFOVgeo (the smallest visible object)

The geometric resolution (spatial resolution). The degree of resolution of the detector in combination with the lens. The geometric resolution is indicated in mrad (= billion) and determines the smallest object that, depending on the distance to the measured object can be displayed on the IR image. In the infrared image of the size of the object corresponds to one pixel.

IFOVmeas (as measured by the smallest item)

Determination of the smallest object to be measured for which a precise measurement of temperature imager. This object is 2-3 times greater than the smallest visible object (IFOVgeo). There follows a rule of thumb: IFOVmeas »3 x IFOVgeo. IFOVmeas also referred to the measured point.


The procedure for obtaining and comparing the readings (actual value) and standard instrument readings (nominal value). Using these results we can conclude - whether the nominal instrument within the allowable range. In contrast to the setup procedure, the deviation of the set is documented, but there is no adjustment device under nominal

value. The frequency of calibration depends on the measurement objectives and requirements to them.

Kelvin [K]

The unit of temperature. 0 K is absolute zero (-273.15 ° C). Accordingly: 273.15 K = 0 ° C = 32 ° F. K = ° C + 273.15.

An example of converting 20 ° C in K: 20 ° C + 273.15 = 293.15 K.

CAT (reflected temperature compensation)

In the fall of the real body of a certain amount of infrared radiation is reflected. This reflected the temperature should be considered when measuring objects with low emissivity. Using the reflected temperature compensation in camera, the reflected radiation is calculated and, thus, improves the accuracy of temperature measurement. Basically, this compensation is performed by entering data in the thermal and / or software that runs manually. In most cases, the compensation temperature corresponds to the reflected ambient temperature. If the infrared radiation coming from sources of interference are reflected on the surface of the measured object, you should determine the temperature of the reflected radiation (for example, using a thermometer or a spherical radiator Lambert). Reflected temperature compensation has little effect on objects with very high coefficient of radiation.


The transformation of matter from gaseous to liquid state. Humidity may condense on the surface if the surface temperature and, consequently, the air temperature at the surface is lower than the ambient air temperature and dew point temperature.


Moving the heat in accordance with the movement of infrared energy in a liquid or a gas flow of the substance (forced or spontaneously).


The degree of ability of a material to emit (highlight) the infrared radiation. Emissivity varies depending on the properties of the surface material, and - for some of the materials - the temperature of the object.

The reflection coefficient

The degree of the ability of a material to reflect infrared radiation. The reflection coefficient depends on the properties of the surface temperature and the type of material.


The degree of ability to pass through a material infrared radiation. It depends on the thickness and material type. Most materials do not miss the long-wave infrared radiation.

Emitter Lambert

The emitter / radiator Lambert - an object that reflects the incident radiation with optimal diffusion, in other words, the incident light is reflected with equal force in all directions. You can measure the temperature of the reflected radiation emitter using thermal Lambert.

Laser (laser measurement point selection)

With the help of the laser is "targeting" in the measured surface (red dot is projected onto the measured object). The laser "pointer" and the center of the image is not entirely consistent with each other as they are on different optical axes. Thus, the point marked by the laser is not suitable for accurate allocation of positions on the screen with the cursor. It serves only as a guide.

Please note:

Laser Class 2: Never point the laser at people or animals and do not look at laser laser. The risk of eye damage!

NETD (temperature sensitivity)

The key term used in connection with the smallest temperature difference that can "recognize" the imager. The smaller this value, the better the resolution of the imager.


The size of the field of view thermal imager and as a consequence, the size of the measurement varies depending on the lens. Wide-angle lens (eg, 32 ° standard lens for testo 880) is ideally suited for the review of the temperature distribution over a large surface. For accurate measurement of small parts (even at large distances) recommend the use of a telephoto lens (eg 12 ° telephoto Testo).

Field measurements of

See IFOVmeas.

Relative humidity (% RH)

The index of saturation of air with water vapor as a percentage. For example, at 33% RH air contains about one third of the maximum amount of water vapor, which can absorb the air at a given temperature and air pressure. When humidity exceeds 100%, and the process of condensation, as air is completely saturated and can not absorb additional moisture. Thus, the gaseous water vapor contained in air is converted into a liquid. The higher the temperature the more moisture it can absorb without the formation of condensation. Consequently, condensation occurs primarily on cold surfaces.

Real body

See the "gray-body radiator."

Thermal Imager

The camera measures the infrared radiation and converts the received signals in the IR image. With the help of the thermal imager, you can get a map of temperature distribution on the surface, which can not be seen by the human eye. Typical applications of the imager are building thermography, service of electrical and industrial thermography.


A variable indicating the energy which is present inside a body.

Temperature scale Celsius [° C]

The unit of temperature. At normal pressure, the zero mark on the Celsius scale (0 ° C) is the temperature at which water freezes. Another fixed point is the Celsius scale the boiling point of water at 100 ° C.

° C = (° F -32) / 1.8 or ° C = K - 273.15. Thermal conductivity Thermal conductivity. The transfer of infrared energy between adjacent particles.Energy is always transferred from warmer to cooler particles. In contrast to the convection conductivity of the particle does not move.


See the IR image.


The procedure for creating images with the help of a measuring technique based on infrared imaging and temperature distribution on the surface of an object using the thermal imager.

The dew point / dew-point temperature

The temperature at which condensation of water. When the dew point temperature of the air is saturated with more than 100% water vapor.Because air can not absorb more water vapor, condensation occurs.

Scale Fahrenheit [° F]

The unit of temperature, is used mainly in North America. ° F = (° C x 1.8) + 32. An example of converting 20 ° C ° F: (20 ° C x 1.8) + 32 = 68 ° F.

FOV (field of view)

The field of view thermal imager. Field of view is specified as an angle (eg 32 °) and defines an area that falls within the field of view thermal imager. The field of view depends on the detector used in camera and the lens used. Wide-angle lens has a large field of view, a telephoto lens (eg 12 ° telephoto Testo) - a small field of view.

Color radiator.

An object with emissivity less than unity, this ratio depends on temperature and varies based on the testimony of the latter. Most metals are emitters of colored body, so, for example, the emissivity of aluminum is increased by heating the metal (= 0.02 at 25 ° C,? = 0.03 at 100 ° C).

The color palette

The choice of colors for the IR images in camera (eg, color palette, "Rainbow", "iron", "halftone"). The contrast of IR images can be displayed in different capacities depending on the measurement problem and adjusting the color palette. Color palette can also be individually configured using the software for analysis (for example, Testo IR Soft 2.0) after saving the IR image. Do not forget about the possibility of your interpretation of infrared images in choosing the color palette. The colors red and yellow hues when viewed intuitively associated with the heat, shades of green and blue - with a cold.

Frequency of updates

Technical data in Hz, indicating the number of updates the display in the second (for example, 9 Gts/33 Hz/60 Hz). 9 Hz refresh rate means that the imager updates the infrared image on the display 9 times per second.



The thermal imager testo 870 was specially developed for your applications, in cooperation with heating constructors, building contractors, service engineers and facility management specialists – for example for detecting leakages, localizing cold bridges or visualizing overheated connections.