Testo Tech sheets:
The testo 890 thermal imager for Research and Development

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.