Measurement of relative movement between two phases

Claim 1

Apparatus for measuring the movement of one phase within another phase, the one phase having a different light transmission characteristic than the other phase, comprising a container having walls which are at least partly transparent to radiation and arranged to contain the phases such that the one phase defines a boundary surface in the other phase; an illumination source for illuminating the region of the boundary surface and comprising a light-emitting diode disposed for directing a beam of radiation into said container and a reflector associated with said diode for directing stray light from said diode into said container; means connected to supply said diode with light-producing energy in the form of pulses for permitting increased illumination intensity and digital processing of measured values; an optical imaging system composed of an aperture and a focussing lens located behind said aperture for forming an image of the boundary surface region within said container on a measuring plane; radiation detecting means including two parallel connected light responsive diodes disposed for measuring the radiation intensity in the measuring plane at at least two areas of that region in order to produce an initial indication of the radiation contrast between those areas; and servo means connected to produce, after a selected time interval following production of the initial indication, relative movement of said container parallel to said measuring plane and in the direction between said areas through a distance sufficient to cause the same contrast indication to be produced by said detecting means.