Manufacturing Trend 2011/04, Technical Diagnostics Section

"A universal measurement procedure"

Thermography, as an imaging temperature measurement procedure, primarily involves collecting temperature data (more precisely, thermal radiation intensity values). These data need to be processed appropriately during or after the measurement, followed by the challenge of displaying and/or documenting them.

Depending on the specific measurement task, the requirements for evaluating thermal images can vary significantly. While in some cases determining the specific temperature of individual pixels (measurement points) is sufficient, in other cases, capturing and evaluating entire image sequences is necessary for analyzing desired temperature processes (e.g., in the form of temperature-time diagrams). Fundamentally, we can also differentiate the evaluation (or processing) of data based on the timing: this step can be performed online (live, even in real-time) immediately during the measurement, or through offline (post-processing) of stored digital data, mostly on a PC.

On-site (immediate, live) evaluation

Often, data evaluation and "processed" visualization are required during the measurement itself. The so-called live evaluation is practically part of the operational (user) software in thermal cameras, or an "embedded" extension, integrating its management into the thermal camera's operation process. The following list summarizes the live evaluation functions integrated into most modern products:

• temperature scale
• display of pixel temperature
• cursor temperature display
• minimum/maximum temperature display
• multi-point temperature display
• multi-surface temperature display
• number of temperature color scales
• display of isotherms
• display of stored images
• image gallery display
• differential image display
• display of background-stored images.

Through these functions, for example, during inspection measurements, it is no longer necessary to evaluate thermal images individually afterwards. (Typical application case: temperatures above 50 °C were not detected anywhere – hence, we can conclude that everything is fine.) In addition to the mentioned evaluation possibilities, we also note the potential for triggering measurements, image storage, or even triggering technological processes (if the thermal camera's output is connected to the technology). It is often very helpful, for example, if image storage occurs automatically when a preset maximum value is exceeded.

Software tools for post-thermographic evaluation

When creating thermographic reports, measurement reports, and other documentation, the method shown in our diagram assumes that the processing of special thermographic data only needs to be done with software developed for this purpose – software with special capabilities tailored to the task – until data formats or (image) information are produced that can be further processed by most users using existing Windows programs (text or image editors). The greatest advantage of this is that the convenience features of the latest hardware and software products due to the rapid development of PC technology can be immediately applied during documentation creation without the need to update or replace the specialized thermographic evaluation software.

The uniqueness of thermographic "image" data

Let's start by noting that thermographic data are not actually image data – files containing these are by no means graphic image files. The raw thermographic data (compressed into appropriate files) contain the registered radiation intensity per pixel and all other important data, allowing for the correct calculation of the temperature of each "image" or more accurately, measurement point afterwards. The content of thermographic files generally consists of the following:

• digitized radiation intensity-detector signal from each measurement point
• data on the applied thermal camera type (e.g., short or long wave) and calibration
• additional information for temperature calculation, such as:
  • ambient temperature
  • measurement path transmission parameters
  • measurement (calibration) range
  • camera setting parameters
  • object distance
  • magnification (ZOOM)
  • object emissivity factor
• user-specific notes
• measurement date and time

Thermographic files generally cannot be displayed with common graphic programs. The point-by-point temperatures can only be calculated with the appropriate thermographic software, as it requires a temperature calculation algorithm that corresponds to the physical model of the thermal camera, based on the relationship between radiation intensity and temperature. The specific algorithm is the intellectual property of thermal camera manufacturers and is therefore not freely accessible. This circumstance, along with the significant computational requirements, led to the introduction of various specialized software tools (thermographic evaluation software) for evaluating thermographic data. There are also "converter" type software available that convert raw data into temperature data per pixel using the appropriate algorithm (result: a matrix of digital temperature data, which, however, cannot be scaled or corrected further).

Typical application areas

Below we review the most common application areas and typical examples of thermography. Buildings, architecture

• assessment and qualification of thermal insulation in residential and industrial buildings
• examination of structural element inhomogeneities
• indirect assessment of structures (e.g. localization of weak points in bridges, tunnels, searching for and qualifying reconstructions)
• preparation of building renovation or repair activities, as well as quality control during execution
• discovery of hidden structural elements (fasteners, wooden beams, trusses, voids, pipes)
• searching for causes of moisture penetration

Building and HVAC technology

• detecting leaks and sealing defects
• locating hidden pipes and accurately determining their positions
• optimization and qualification of HVAC equipment operation
• operational verification of heating and cooling equipment (surfaces)

Energy industry

• condition assessment of electrical equipment (transformers, insulators, switches, conductors, cables, connections, distribution equipment in high, medium, and low voltage networks)
• assessment of heat exchangers and district heating pipelines
• identification of heat losses
• assessment of pipe and equipment insulation

Industrial applications in development, manufacturing, and process control

• product development and optimization according to specific thermal requirements
• process optimization under special process temperature requirements (e.g. setting and tuning heating or cooling cycles)
• non-destructive material testing and quality control
• searching for faults in electronic and microelectronic connections and components (e.g. short circuits, thermal overload)
• inspection of electrical equipment (main and sub-distribution boards, switchgear, individual connections, electrical consumers)
• continuous or periodic technological and fire protection inspections (e.g. waste storage, coal storage, wood drying, sand mold walls, conveyor belt bearings)
• liquid level detection (uninsulated storage tanks and pipelines)

Agriculture and environmental monitoring (especially thermography from the air)

• collecting specific data for agriculture or breeding purposes
• exploring substances hidden in the ground (pollutants, thermal springs) or landfill surveys
• microclimatic studies
• prevention and extinguishing of forest fires (discovering hot spots)
• exploration and assessment of thermal loads in rivers, lakes, and wastewater disposal systems

Medical applications

• human and veterinary medicine
• diagnosis of tumors, inflammations, and peripheral circulatory disorders

Rahne Eric (PIM Ltd.) pim-kft.hu, gepszakerto.hu

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