Abstract: In its preferred embodiment, a one-piece optical-prism sensor of liquid level internally incorporates waveguide structure, i.e., within the otherwise conventional conical external profile of the prism, the waveguide being a thin flat member which includes three parallel spaced axes, namely, the axis of light input, the central axis of the cone, and the axis of detection of such light as exits the prism. The conical shape of the prism is essentially a hollow conical shell, within which the waveguide extends in essentially a single diametrical plane, with integral connection of the shell to the diametric limits of the waveguide. The net result is that light enters the waveguide on the input axis and, to the extent that the light is internally reflected, the waveguide so confines internal reflection that scattering is very substantially reduced, and essentially all the internally reflected light will exit on the detection axis.

Abstract: The invention contemplates a sensor head which senses liquid conductivity as well as liquid level. An optical prism is configured to provide two internal reflections of light entering on a first-axis alignment of 45.degree. incidence for the first internal reflection, and exiting the prism on a second-axis alignment that is parallel to and spaced from the first-axis alignment. The internal reflections may occur in a conical-prism configuration having a geometric apex angle of 90.degree., or in a triangular-prism configuration wherein two surfaces converge at 90.degree.. In either case, these internal reflections occur substantially in the single geometrical plane that is defined by the first and second axes. As a matter of structural practicality, each of these prism alternatives has greater body bulk, on both sides of this single geometric plane, than is needed for the indicated internal relfections.

Abstract: Plural sensor prisms and associated opticalfiber circuits are arrayed as a single vertical stem by which the individual prisms serve for response to each of a plurality of different liquid levels. Each prism is formed of light-transmitting plastic material which can be injection-molded to precision dimensions. The body configuration is such as to adapt to arrayed interconnection with tubular members, also of plastic, and bonded at telescoping fit of each prism to the tubular member or members to which it is connected. The prism configuration relied upon for sensed response to the presence of immersing liquid (as compared to air) is a solid region having an exterior profile which includes a downwardly convergent conical surface portion at least at spaced locales which are at equal but opposite offset from the cylindrical body axis, wherein the geometric apex angle of downward convergence is 90 degrees.