Thermography: Your questions, our answers.

Just like the thermal imaging camera, a pyrometer (also known as a radiation thermometer, point pyrometer, temperature measuring gun or infrared thermometer) detects infrared radiation emitted by an object and converts this into temperature readings. However, a point pyrometer only measures the temperature of a single point and displays a measured value, but does not generate an image. As a type of fixed heat sensor, point pyrometers are often used to measure temperatures on high-temperature surfaces, for example in kilns.

The difference between active and passive thermography is that during active thermography measurements, heat pulses are directed at the measurement object. These do not have to be particularly strong. A few tenths of a degree centigrade is usually enough. The heat migrates into the interior of the object. If there is a fault in the thermal conductivity, the surface stays warm for longer. Passive thermography, on the other hand, does not require an external heat source. Here, the temperature distribution of a surface is measured using the intrinsic heat of the object.

Active thermography is used to detect adhesion weaknesses, cracks, delaminations, bubbles, air pockets or corrosion in objects. The strength of welded, glued or soldered joints can also be tested using active thermography.

Passive thermography for temperature measurement and monitoring is extremely versatile and is therefore used in a wide range of industries and environments. These include industry, building management, the automotive, electrical and medical engineering sectors as well as research and development, but also safety, search and rescue and firefighting. Passive thermography is also used to detect thermal bridges in building technology.

The measurement takes place directly at the surface, so that the depth effect is practically zero.

It is important to ensure that the outside walls of the building are not exposed to the sun either before or during the measurement. Even light winds can falsify the measured values in outdoor thermography.

Thermography measurements are best carried out in the dark to prevent falsified values due to solar radiation.

Thermographic testing of electrical installations in accordance with DIN 54191 is a mandatory measurement procedure that must be carried out regularly to check safety and functionality. This applies in particular to areas in industrial buildings such as factory halls and warehouses. If the installation has passed the standard test, an official certificate and a test seal with the date of the next test are issued. The inspection intervals depend on the type, complexity and size of the installation. 

Training courses in accordance with DIN 54162 are relevant for groups of people from the fields of energy consulting, building damage assessment, architecture, building biology and civil engineering, as well as for managers and responsible employees of craft businesses and for claims managers in the insurance industry. The training courses cover content such as regulations, guidelines and standards as well as the presentation of various thermography systems, heat and temperature measurement, the basics of radiation physics, IR camera technology and measurement parameters, camera operation, thermograph analysis, passive and active thermography, practice in detecting thermal bridges, air leaks and moisture penetration as well as practical guidelines for successful (legally binding) reporting. The examination is conducted by the independent personnel certification centre of the TÜV, and is concluded with the certificate "Specialist for thermography (TÜV) in accordance with DIN 54162 and EN 473".

When buying a thermal imaging camera, a key selection criterion is the type of installation you wish to inspect. If, for example, mechanical or electrical problems need to be detected as quickly as possible during maintenance, then ergonomic and user-friendly cameras are particularly suitable. They offer sufficient flexibility for a wide range of applications. Thermal imaging cameras with special lenses such as wide-angle or telephoto lenses are useful if measurements are to be taken from a greater distance, for example in areas with motor control units that are difficult to access or on high-voltage systems. When it comes to measuring very high temperatures, such as on rotary kilns, thermography devices should be able to be calibrated accordingly. The most important selection criteria for a thermal imaging camera include 

• Thermal resolution: The higher the thermal resolution, the smaller the temperature differences that can be detected. 
• Measuring range and accuracy: The measuring range should meet the requirements of the intended application and the accuracy of the device is crucial for precise measurements. 
• Image quality and resolution: Higher image quality and resolution enable more detailed images, an aspect that is important for identifying problems. 
• Image overlay and merging: The possibility of overlaying thermal images with optical images makes it easier to localise problem areas.
• Measuring speed: Fast measurements are important in some applications, e.g. when monitoring rapidly changing processes.
• Portability and ergonomics: Lightweight, handy devices with simple operating elements increase user-friendliness, mobility and flexibility.
• Data storage and transmission: The ability to store and easily transfer data is important for documentation and analysis. 
• Battery life: Long battery lives are particularly important for mobile applications or field work.
• Robustness and reliability: A sturdy design and reliability are crucial for use in different environments and conditions.
• Calibration options: Regular calibration options are important to ensure the accuracy of the thermal imaging camera.

Zu den wichtigsten Lieferanten für eine Wärmebildkamera zählen:

• BEHA
• Chauvin Arnoux
• Fluke
• Teledyne Flir

You can find these and other manufacturers in our Online shop.

Temperature is a physical property that describes the heat intensity of a system or object. It is a measure of the average kinetic energy of the particles of a substance and is usually expressed in degrees Celsius or Kelvin.

Thermal energy is a form of energy that is released or absorbed by an object due to its temperature. It is caused by the movement and arrangement of atoms and molecules within a system and can be transferred by heat conduction, convection or radiation. In physical processes, thermal energy is often used to perform work or bring about other changes in a system.

There are four main types of temperature transfer: Heat transfer, heat conduction, convection and radiation. Heat transfer is the flow of heat from a solid into a liquid or gaseous medium or vice versa. Heat conduction takes place in solids, while convection refers to the transfer of heat through the flow of a medium such as air or water. Radiation is the transfer of thermal energy by electromagnetic waves that do not require a medium such as air, e.g. in the vacuum of space.

The electromagnetic spectrum covers a wide range of electromagnetic waves, including thermal radiation and visible light. Thermal radiation lies in the infrared range of the spectrum and its waves are longer than those of visible light. Thermal radiation is detected by thermal imaging cameras that are used to visualise the temperature distribution in or on objects.

Infrared (IR) is a part of the electromagnetic spectrum that lies between visible light and microwave radiation. This radiation has longer waves than visible light and is invisible to the human eye. Infrared rays are generated by the heat radiated by objects or by certain electrical processes. IR is used not only in thermography, but also in various everyday applications such as remote controls, night vision devices and infrared heaters.

Infrared radiation is used in thermography to visualise the temperature distribution of objects. Thermal imaging cameras detect this infrared radiation and convert it into an image that shows the different temperatures of the surfaces. This allows hot spots, cold spots and other temperature anomalies to be quickly identified, which is beneficial in various areas such as building thermography, electrical thermography, medical diagnostics and security surveillance.

Thermal imaging cameras operate in the infrared range of the electromagnetic spectrum. The most widely used cameras operate in the long-wave infrared (LWIR) range. This typically covers wavelengths between 8 and 14 micrometres. Thermal imaging cameras detect the heat radiation emitted by objects and convert it into a false-colour image, making temperature differences visible.

Cooled cameras are used in thermography when greater sensitivity and accuracy are required, for example when examining objects with very high temperatures or fast-moving objects. Cooled cameras offer better image quality and higher thermal sensitivity compared to uncooled cameras, making them particularly suitable for applications in scientific research, industrial quality control and military surveillance.

The radiation properties of materials have a significant influence on thermography. Factors such as the surface texture and composition of a material determine how well infrared radiation is absorbed and emitted. The emissivity is based on these properties. Materials with high emissivity can emit infrared radiation more efficiently than materials with lower emissivity. Precise knowledge of the radiation characteristics is crucial for carrying out accurate thermographic measurements and obtaining correct temperature values.

The distance to the measured object plays an important role in thermography. The further away the object is from the camera, the larger the image section and the fewer details can be captured. In addition, the accuracy of the temperature measurement can decrease as the resolution of the camera decreases in relation to the distance. It is important to select the optimum distance according to the requirements of the measurement in order to achieve accurate and meaningful results.

Due to its high transmittance of infrared radiation, monocrystalline germanium is ideal for use in thermal imaging cameras and is therefore frequently used as a material for infrared optics.

Proper care of a thermal imaging camera includes the regular removal of dust. Special cleaning cloths suitable for optical surfaces can be used for this purpose. The sensitive lenses should only be cleaned by a specialist to avoid damage. Please contact our service team.

The following lenses are available for thermal imaging cameras: 

• Macro lenses for the close-up range 
• Telephoto lenses (12 degrees) 
• Super telephoto lenses (6 degrees) 
• Super wide-angle lenses (80 degrees)

Dual Field of View (DFOV) is a function that can be found in some high-quality thermal imaging cameras. It allows the user to choose between two different focal lengths or fields of view without having to change the optics. This allows the user to switch between a broader overview and a more detailed view of the target object as required, without having to physically reposition the camera. This function is particularly useful in applications where flexible adjustment of the field of view is required, such as when monitoring large areas and simultaneously inspecting objects at close range.

A measuring spot is the smallest area on an object that a thermal imaging camera can detect and whose temperature it can determine. A simple method based on a 3x3 pixel average is used to determine a measurement spot. The camera determines the temperature based on a small area of 3x3 pixels around the target point. 

For a more precise determination of the measuring spot, reference spotlights and reference apertures are required and 40 to 45 measurements are carried out. The temperature difference is determined between a reference radiator, which emits a known temperature, and the size of the aperture through which the radiator surface can be seen. The exact temperature of the measuring spot is determined by comparing these two measured values.

Thermal imaging cameras are available with different resolutions; the resolution indicates the number of thermal pixels that the camera can capture. The most common resolutions are as follows: 

1. Low resolution (e.g. 80x60 pixels): This resolution is suitable for basic applications where a rough visualisation of temperature differences is sufficient but detailed imaging is not required. 
2. Standard resolution (e.g. 320x240 pixels): This resolution offers a balanced combination of image quality and cost. It is suitable for a wide range of applications, from building inspections to industrial maintenance. 
3. High resolution (e.g. 640x480 pixels or higher): This resolution provides detailed and precise imaging, making it ideal for demanding applications such as medical diagnostics, research or military applications. However, cameras with a high resolution are often more expensive. 

Thermal imaging cameras can be used in many different ways, but there are various sources of danger to the device. Direct sunlight on the sensor with a temperature of approx. 5,700 K, for example, can destroy the sensor. Irradiation of the sensor with a CO2 laser with a wavelength of 10.6 µm or the high temperature of the arc as well as spattering metal particles during arc welding can also lead to damage.

With thermography, a temperature range must be selected so that the camera correctly determines the relevant temperature differences within the observed range. This ensures that the camera is not overloaded and that all relevant details are visible in the image. A temperature range that is too wide may not be able to detect subtle temperature differences, while a temperature range that is too narrow may result in important information being lost outside this range. Selecting the right temperature range is therefore crucial to obtaining accurate and meaningful thermographic images.

Level and span are settings used in thermography to adjust the contrast and display of temperature differences in an image. Level controls the average grey value of the image and allows the background to be adjusted, while Span defines the temperature range displayed in the image. By adjusting the level and span, users can improve the visibility of thermal features and reduce background noise. In this way, Level and Span help to improve the quality and informative value of thermographic images.