Two Wavelength Measurement

Two-wavelength measurement, also known as ratio pyrometry or two-color measurement, is an advanced non-contact temperature measurement technique that quantifies the ratio of radiation intensities at two distinct wavelengths instead of directly evaluating radiation intensities. This method facilitates precise temperature measurements, even under conditions of varying emissivity or partial obscuration of the measuring object. The technology leverages the fact that a material’s emissivity varies at different wavelengths. By calculating the ratio of the measured intensities, a temperature-independent quantity is derived, enabling accurate temperature determination. This applies strictly if the influence of the process under consideration or the environment on the emissivities of both wavelength signals is the same.

To make this possible for many applications, two detectors with spectral ranges that are close together or even partially overlapping are usually used. However, even then, both emissivities are often only similar to one another. It has therefore become common practice to adjust the ratio of both emissivities, the so-called slope. This is often approximately constant, even if the individual emissivity levels are not.

Two-wavelength measurement is particularly advantageous in industrial applications characterized by high temperatures and challenging measurement conditions. Key benefits include emissivity independence, which ensures precise measurements even with unknown or variable emissivity of the material. The technique also exhibits robustness, demonstrating resilience to contamination or partial obscuration of the measuring object, and provides high accuracy and speed, offering rapid and precise measurements crucial for industrial processes.