ManufacturingTrend 2015/11, Technical diagnostics section

Modern thermal cameras from a professional perspective (IX)

Selection criteria summarized

In the final chapter of our series, we review step by step the task-specific selection criteria for thermal cameras suitable for specific thermographic measurement tasks.

1) Installed or mobile?

• An installed thermal camera cannot be used for handheld measurements because it lacks both a battery and controls, as well as its own display (carrying a continuously connected notebook is impractical),
• A portable thermal camera cannot be used for installed tasks that require cooling/heating, moisture and dust protection, as protective covers of this kind are typically only available for installed types.

2) Wavelength range

The long-wave range cannot be used

• only for objects with high emissivity in the mid-wave range,
• if there is glass (or other material that does not transmit long waves) between the object and the thermal camera

The mid-wave range cannot be used

• for measuring low-temperature objects,
• for measurements from large distances (several times larger than 10 m),
• only for objects with acceptable emissivity in the long-wave range,
• for materials between the object and the thermal camera that do not transmit medium wavelengths.

3) Detector technology

Considerations: wavelength, frame rate. Bolometer/microbolometer sensor can be used if

• a long-wave device is required and
• a maximum of 50/120 Hz (or up to 240 Hz for special thermal cameras) frame rate is sufficient. (Note: for free-hand thermal camera use, to avoid problems caused by motion, the minimum required frame rate is 50 Hz.)

Photon detectors are necessary if

• measurements need to be taken in the mid-wave range (e.g., through glass) or
• a frame rate above 50/120 Hz (or in exceptional cases 240 Hz) is required. (Note: photon detectors are significantly more expensive than bolometers and also require cooling, which depending on the technology, imposes a limitation on lifespan.)

4) Thermal resolution

• to be considered based on the specific task,
• not critical for checking boilers and furnaces, or assessing mechanical or electrical equipment conditions, as fault locations (thermal phenomena) involve large temperature differences,
• important for searching for moisture/leaks, assessing insulation, fire-resistant linings (wear),
• usually the most essential parameter for biological or material testing measurements. (Note: improving thermal resolution results in sharper, clearer, and more recognizable thermal images.)

5) Temperature measurement range

• to be considered based on the specific task,
• important quality parameter primarily for measuring low-temperature objects.

6) Number of pixels

• absolute minimum: 160×120 pixels (effective operation is hardly possible with fewer pixels),
• recommended minimum: 256×256 or 320×240 pixels,
• economical: 384×288 pixels,
• professional: 640×480 or 640×512 pixels,
• current peak: 1024×768 pixels,
• favorable solution: quadrupling pixels with microscan (up to 1280×960 or 2048×1536 pixels, can be used with or without a stand; not interpolation calculations, but real measurement points). (Note: the more pixels the camera has, the more details become recognizable in the image, or the larger object (equipment) can be examined at once with appropriate, i.e., evaluable resolution.)

7) Geometric resolution

• to be considered based on the specific task,
• for multiple tasks, it is preferable to choose a thermal camera with interchangeable lenses so that the appropriate geometric resolution is always available,
• a favorable solution without interchangeable lens: quadrupling pixels with microscan procedure, which improves the geometric resolution to 2/3 of the value specified for the same detector-optics assembly.

8) Special capabilities

• quick internal storage of thermal image sequences without a PC,
• remote control, live data transmission,
• interchangeable lenses, special filters.

The parameters of thermal cameras designed for various tasks are listed in the table on the following page.

professional field	spectral range	technology	calibration range	number of pixels	geometric resolution	temperature resolution	image acquisition frequency	recommended functions/accessories
building thermography	8...12 µm	bolometer (photon detector is also good but expensive)	min. -20°C ... 100°C better from -40°C (approximate upper limit)	min. 320x240 better 384x288 recommended 640x480 peak 1024x768	min. 1.5 mrad better 1 mrad + telephoto lens	min. 80 mK better 50 mK best 30 mK (30mK: can measure for several days = better return)	manual capture: min. 50 Hz	- selectable color scale - autofocus - telephoto lens - wide-angle lens
electrical equipment measurement	8...12 µm	bolometer (photon detector is also good but expensive)	min. -0°C ... 150°C better -20°C ... 250°C	min. 160x120 better 320x240 recommended 384x288 or 640x480 peak 1024x768	min 2 mrad better 1.5 mrad best 1 mrad	min. 120 mK better 80 mK best 50 mK	manual capture: min. 50 Hz	- selectable color scale - autofocus - digital video camera - composite imaging - digital sound recording
measurement of mechanical equipment	8...12 µm	bolometer (photon detector for moving objects, fast processes)	min. -20°C ... 250°C better -40°C ... 400°C	min. 160x120 better 320x240 recommended 384x288 or 640x480 peak 1024x768	min 2 mrad better 1.5 mrad	min. 120 mK better 80 mK best 50 mK	manual recording: min. 50 Hz moving objects: >>50 Hz	- selectable color scale - autofocus - sequence recording - differential recording - digital video camera - composite imaging - digital sound recording
medical (biological) measurements	8...12 µm	bolometer (photon detector is also good, but expensive)	min. -20°C ... 50°C better from -40°C (approximate upper limit)	min. 320x240 better 384x288 recommended 640x480 peak 1024x768	min. 1.5 mrad better 1 mrad	min. 50 mK better 30 mK best 10 mK	manual recording: min. 50 Hz	- selectable color scale - autofocus - sequence recording - differential recording - high image homogeneity - composite imaging
glass-related measurements	3...5 µm (8...12 µm only for glass surfaces)	photon detector	min. 100°C ... 1200°C better 0 ... 2000°C	min. 320x256 recommended 640x512 peak 1280x1024	min 2 mrad better 1.5 mrad	min. 120 mK better 80 mK	process-dependent (typical >>50Hz)	- selectable color scale - autofocus - sequence recording - differential recording - special filters - macro lenses - microscope lenses - protective windows
microelectronic measurements	8...12 µm (3...5 µm is also good, but expensive)	bolometer (photon detector for fast thermal processes)	min. -0°C ... 150°C better -20°C ... 250°C	min. 320x240 better 384x288 recommended 640x480 peak 1024x768	min. 1.5 mrad recommended 1 mrad better 0.7 mrad +special lenses	120 mK better 80 mK best 50 mK	> 2 x process frequency (min. 50 Hz)	- selectable color scale - autofocus - sequence recording - differential recording - macro lenses - microscope lenses - pixel-wise emissivity correction - fast thermal imaging
metallurgical measurements	8...12 µm or 3...5 µm	bolometer or photon detector	min. 300°C ... 1200°C better 0 ... 2000°C	min. 160x120 better 320x240 recommended 384x288 or 640x480 peak 1024x768	min 2 mrad better 1.5 mrad	120 mK better 80 mK	manual recording: min. 50 Hz	- selectable color scale - autofocus - sequence recording - differential recording - digital video camera - composite imaging - telephoto lens - protective windows - additional cooling - special filters
industrial insulation measurements	8...12 µm	bolometer (photon detector is also good, but expensive)	min. -20°C ... 300°C better -40°C ... 600°C	min. 320x240 better 384x288 recommended 640x480 peak 1024x768	min. 1.5 mrad better 1 mrad	120 mK better 80 mK best 50 mK	manual recording: min. 50 Hz	- selectable color scale - autofocus - sequence recording - differential recording - digital video camera - composite imaging - digital sound recording
measurement of electrical power lines	8...12 µm	bolometer (photon detector is also good, but expensive)	min. -20°C ... 120°C better -40°C ... 300°C	min. 320x240 better 384x288 recommended 640x480 peak 1024x768	min. 0.3 mrad recommended 0.2 mrad better 0.1 mrad	120 mK better 80 mK best 50 mK	manual recording: min. 50 Hz	- selectable color scale - autofocus - "large" telephoto lens - digital video camera - composite imaging - digital sound recording - GPS data management

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

Contact

The content of the publication is protected by copyright, and its (even partial) use, electronic or printed re-publication is only permitted with the indication of the source and the author's name, and with the author's prior written consent. Violation of copyright (Copyright) will have legal consequences.