4. Optical effect systems

4.1 Measuring principle

A light beam (wavelength λ: from ultraviolet λ > 50 nm to infrared λ < 1 mm) can be interrupted, deflected, refracted, reflected, attenuated or scattered when an obstacle, such as a liquid or bulk solid, gets in its way: all these phenomena can offer a solution for detecting an interface.

The simplest system, with beam shielding, consists of a light source, the medium to be analyzed and the receiver-detector. In addition, transparent windows are required for liquids or bulk products. A filter can be interposed to work on a narrow wavelength range and thus increase the selectivity of the method.

Daylight, with its broad spectrum, is a disturbing factor, as is ambient lighting. Many optical systems are all...