GB387425A - Improvements in or relating to liquid level gauges of the transparent prism type - Google Patents

Abstract

387,425. Indicating liquid-levels. ELECTRICAL IMPROVEMENTS, Ltd., Carliol House, Newcastle-on-Tyne, and BLACKBURN, C. L., 2, Ryder Street, London. Oct. 8, 1931, No. 27969. [Class 12 (i).] A liquid-level gauge comprises a prism so arranged that light entering the gauge above the liquid is totally reflected so that the upper part appears dark, while light entering below the liquid level is refracted through the liquid so that the lower part appears bright. In Fig. 1, two similar glass prisms A, B are mounted vertically with their inclined faces separated to form, with internal shoulders D<1>, a space for the water column. The prisms are clamped in a casing D against inset pieces E, E<1>. Light is directed through the opening E<2> and is incident on the oblique surface of the prism at an angle to the normal greater than the critical angle for the upper part, and less than the critical angle for the lower part of the surface in contact with the liquid. The upper part of the beam is thus totally reflected, while the lower part is refracted and passes through the second prism to emerge at E3. In a modification, Fig. 3 (not shown), the prisms are mounted in a recess in the casing and are secured by a slotted cover-plate held by screws. In another modification, Fig. 6 (not shown), one of the prisms is replaced by a parallel-sided glass plate, and the light may be incident from either side. Specifications 263,638, [Class 123 (i), Liquid-level regulating &c.], and 387,752 are referred to.