Excerpt: Tech sheet – testo 890: see more thanks to excellent temperature measuring accuracy.





The testo 890 thermal imager has one of the best temperature measuring accuracies in their instrument class. This means they are ideally suited for tasks in research and development which require the utmost precision.

Testo guarantees a measuring accuracy of ±2°C or ±2% for the testo 890 thermal imager. These values do not just apply to one or two individual reference points, but to the whole thermal image and every individual measuring value. Furthermore, the temperature measuring accuracy is also guaranteed over the entire ambient/operating temperature from -15°C to +50°C. Why is that the case?


The sensor is the heart of every thermal imager. It comprises a matrix with very small infrared-sensitive pixels which convert the incident electromagnetic radiation of the measurement object into an electronic signal. The entirety of the pixel signals create a digital image. The digital image shows the surface temperature of the object and depicts this as a false colour image in the camera. The process involves every individual pixel getting a temperature value by scaling and the selected palette a defined colour in the false colour image. The speed of a thermal imager depends on the time required to create an individual image. The testo 890 thermal imager has an image refresh rate of up to 33 Hz.

The detector of a Testo thermal imager can measure electromagnetic radiation in an atmospheric window between 7.5 and 14 µm. The ambient temperature (300 K) has the highest radiation intensity at a wavelength of 9.89 µm (Planck's radiation spectrum). A Testo thermal imager's detector is therefore designed to have the highest sensitivity at the 9.89 µm wavelength.


The sensor also has a high thermal sensitivity. This is to be understood as the smallest temperature difference which the detector can measure and visualize. Thermal sensitivity is also referred to as Noise Equivalent Temperature Difference (NETD) and given in millikelvins (mK). NETD is therefore the smallest resolution of the temperatures between 2 pixels. NETD is improved by the use of lenses with particularly large apertures. The better the NETD is, the more low-noise and high-contrast the image is with the same number of pixels.


Testo's thermal imagers have an uncooled detector using microbolometer technology. This means the detector is not only influenced by the electromagnetic radiation of the object being measured, but also by the ambient temperatures of the thermal imager itself. As the figure shows, a mere 5% of the whole electromagnetic radiation originates from the object being measured. The influences of the remaining 95% of the radiation must therefore be compensated for exact measuring values. Because these influences change with the ambient temperatures, Testo fits several high-precision temperature sensors in the housing. These ensure that the sensor's ambient temperature does not falsify the measuring values.


The influences of the ambient radiation which are measured by the temperature sensors are compensated by adjustment. Careful adjustment meticulously carried out is therefore crucial for excellent temperature measuring accuracy. Testo carries out the adjustment of thermal imager at ambient temperatures between -15°C and +50°C. Every pixel of the testo 890 camera gets its own detailed sensor characteristic curve which ensures its measuring accuracy at different ambient temperatures. The excellent temperature measuring accuracy of the testo 890 is therefore based on the precisely set interplay between detector, lens and adjustment.

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  • Design and sensitivity of the infrared detector 
  • Detailed analysis options due to minimum focusing distance
  • Improvement of resolution through the testo SuperResolution Technology
  • Fast and precise analysis via the LabVIEW™ interface

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