Abstract: A flat light beam is projected from a light projecting unit to an object to be measured, sweeping its surface with a bright line. The image of the bright line is focused on pluralities of photosensor arrays and line photosensors. A plurality of positions in the bright line are computed by triangular surveying, based on the direction of projection of the flat signal light beam and the positions of those photosensors in each array from which the signal light component is obtained. The position of a gap in the surface of the object is computed, using the detected positions of the photosensors and a signal which indicates a dropout of the signal light component from the output of a line photosensor.

Abstract: A measurement head in an arc welding machine modulates the light intensity of a laser light beam with a modulating signal of 50 KHz or higher, and radiates the laser light beam onto an object to be measured while changing the direction of laser beam emission in one plane. A light receiving unit in the measurement head changes its direction of detecting a reflected beam in the same plane. Angles at which the light beams are emitted and detected are detected at the time a modulated signal component is detected from an output from the light receiving unit. The position of a bright spot produced on the surface by the radiated laser light beam is computed from the detected angles based on the principle of triangulation.

Abstract: Only one reversible electro-acoustic converter is used to act without a press-to-talk switch or the like as a transmitter and a receiver. The electro-acoustic converter is connected to a communication line through two 2 - 4 converters in the form of hybrid transformers which are interconnected to form a transmitting system and a receiving system.