Combined liquid-level and conductivity sensor

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. For conductivity-sensing purposes, the invention uses this bulk, on opposite sides of the plane of internal reflections, to position two spaced electrodes, for external exposure at substantially the level of the internal reflections but at lateral offset from the plane of the reflections. Electronic circuitry associated with the prism serves the light-source and photodetection purposes of liquid-level response, in addition to serving the conductivity response, if any, of electrode exposure to immersing liquid.