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testo explains the theory of thermography

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Thermography is a passive, contactless temperature measurement method using a thermal imager to measure infrared radiation in objects.

Every object with a temperature above absolute zero (0 Kelvin = -273.15C) emits infrared radiation, which is invisible to the human eye. Since there is a correlation between the temperature of an object and the intensity of the infrared radiation it emits, a thermal imager is employed to measure the long-wave infrared radiation received within its field of view, from which it calculates the temperature of the object.

The calculation factors in the emissivity (ε) of the surface of the measuring object and the compensation of the reflected temperature (RTC = reflected temperature compensation), both variables that can be set manually in the thermal imager. The thermal image shows the temperature distribution on the surface of an object. Each pixel of the detector represents a thermal spot that is shown on the display as a false colour image. 

It is important when taking a thermal image to choose the right subject area, and focus the thermal image correctly on the area relevant to the measurement. 

Tips for taking the thermal image using a thermal imager:
  • Factor in, prevent or screen all sources of interference
  • Surface of the measuring object should be clear of optical and thermal sources of interference
  • Where possible, remove covers and objects causing interference from the environment
  • Change position when taking the measurement in order to identify any reflections
  • Thermal features of the measuring object remain in the same place even if the slant changes
  • Measuring spot should never be bigger than the measuring object
  • Keep the measuring distance as small as possible
  • Use a lens appropriate to the measurement task
  • Stand recommended for exact measurement of details
testo specialises in the supply of a comprehensive range of thermal infrared cameras designed for use in diverse thermography applications.

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