Slope

In ratio pyrometry (also known as two-wavelength measurement), the radiation signals of an object are evaluated by two infrared detectors that are considered independent of each other and have different spectral sensitivities. Since the emissivity for many probes (e.g., all metals) depends on the spectral range, the emissivity for both signal channels is different. Since the signal ratio is now further processed, the emissivity ratio is relevant for the temperature calculation and not the absolute values of the individual emissivities.

The emissivity ratio is summarized and referred to as the slope, with slope = e1/e2. While the values for emissivity in practice range between 0.07 and 0.95, the values for the slope are typically between 0.7 and 1.3.