PHOTOELECTRIC INCLINATION SENSOR

A method for obtaining the tilt angle and direction in the two-dimensional plane by using a photoelectric inclination sensor, consisting of LED, a hemispherical spirit level and a photodiode array is explained. Light from the LED projects a bubble in the spirit level and throws a shadow onto the surface of the array composed of four equivalent p-n junction diodes, isolated from each other by a cross on a wafer. When the sensor is kept horizontal, the area of the shadow in each diode is exactly equivalent. But when it is inclined, the area is not equivalent. Assuming that the shadow on the array in a low tilt angle is circular and the output current per unit area is constant over the surface of the diodes, the tilt angle and direction in a two-dimensional plane is obtained by combining the diode outputs. The principle of the sensor, its fabrication process, theoretical analysis of the sensor output against tilt angle and direction, and the system to display them in CRT are explained. Finally, the experimental values are discussed. © 1990.