Remote position control and indication by digital means

In some applications, e.g. on an accurate radar equipment, it is desirable to convert the angular setting of a shaft to digital form with high accuracy. A master binary disc is made photographically on a dividing engine. A photographic copy of the disc is coupled directly to the shaft whose setting is to be measured and is scanned to produce a digital signal representing the shaft angle or a function thereof. A number of convertors were made with scales subdivided to give an accuracy of the order of 1¿ of arc. They were used under conditions of severe vibration and exposure, and amply demonstrated the principle of the high-accuracy binary disc. A follow-up servo mechanism was made and demonstrated, in which one shaft followed another by a digital link, to an accuracy of 1¿ of arc. The limitation of accuracy is in the production of the binary discs. The master pattern can be subdivided and the photographic emulsion has ample resolution, but further work has to be done on the avoidance of small blemishes in the photographic processes.