Apparatus for the continuous measurement of the density of a liquid by utilization of the law of refraction

Claim 1

Apparatus for the continuous measurement of the density of a liquid within prespecified limits by utilization of the law of refraction, particularly for the continuous measurement of the acid density of a storage battery of a motor vehicle for the purpose of determining the state of charge of the battery, comprising: an elongated light-transducing rod mounted for immersion into the liquid; a measuring surface located at the immersion end of said rod; a light source mounted to emit a pencil of rays which is at least nearly parallel into said rod toward said measuring surface; said measuring surface being positioned on said rod to direct said pencil of rays at an angle taken with respect to a normal to the said measuring surface that equals at most the total reflection angle occurring at the lower density limit of said liquid; a deflecting surface 18 arranged in the path of said pencil of rays for deflecting rays refracted into the liquid by the measuring surface; a photosensitive element located in the path of said pencil of rays refracted by the said measuring surface into the said liquid and subsequently deflected by the deflecting surface; a plane (22) normal to the said deflecting surface being positioned to enclose with the said pencil or rays the Brewster angle (αB) occurring at the greatest density of the liquid.