Linear and angular transducers for positional control in the decametre range. A survey of available techniques

Currently available methods for transducing large-scale (over 1 m range) multiaxial position into equivalent signals for closed-loop control or direct measurement are reviewed. Methods discussed are: mechanical techniques (automated tapes and wires, friction-driven rollers); distance measurement with radiated energy (microwave, acoustic, modulated and pulsed-incoherent and -coherent light); natural-phenomenon references (gyrocompasses, magnetic compasses, celestial-body position, electric levels, horizon sensors); optical position determination (detector position-indicating properties, tracking optics, photogrammetry, mechanically and electrically scanned imaging optics); automatic alignment (wires, interference and diffraction optical elements, autocollimators, laser beam, spatially modulated beams); and finally, methods of high-resolution rotary measurement (encoded and incremental, moiré fringe, dual generator, chronometric, synchros, optical interferometry). The concept of triangulated position determination (instead of the usually used rectangulated methods) for large-scale control is described.