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In the range between 4.6 - 4.9 µm, glass has an emissivity of almost 100 %. Above 5 µm, atmospheric influences such as humidity or water vapour affect the measurement. The CellaTemp® PK 42 has a blocking filter with a spectral sensitivity of 4.6 - 4.9 µm. This means that it records the temperature from the area of the glass close to the surface. Thickness changes, different types of glass or humidity changes in the atmosphere do not affect the measured value at this wavelength.