A water film surface is irradiated with light from a detecting unit's light source. Light reflected from the water film surface is converted into an electrical signal by a sensor (photoelectric converting means) in the unit. The converted electrical signal is supplied to a processing unit through a cable....http://www.google.es/patents/US4687333?utm_source=gb-gplus-sharePatente US4687333 - Measuring apparatus for optically measuring the thickness of a water film
Measuring apparatus for optically measuring the thickness of a water film
