A photoelectrical tilt sensor

Abstract

The angle of deflection from the horizontal position can be detected by a sensor that consists of two phototransistors placed symmetrically near a light-emitting diode and immersed in a suitable liquid. In this arrangement the transistors are illuminated by the light reflected from the air-liquid interface. When the sensor is in the horizontal position, both transistors receive equal fluxes, causing the net electrical signal to be zero. In any other position the symmetry is interrupted and the signal becomes dependent upon the tilt angle. The characteristics of the sensor is S-shaped, but has a nearly linear part around the origin. The sensor response there is about 42 m V/degree.