Electro-encephalographic Signal Averager



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One potential method for obtaining high quality electro-encephalographs is to photographically average the electromagnetic signals of interest. Before any such process can be attempted, however, the concept and feasibility of photographic signal averaging must be demonstrated. The Electro-encephalographic Signal Averager fulfills this purpose. It provides a means to rotate a film-carrying drum through a specified angle at a constant speed. During the constant-speed rotation, optical signals may be recorded on the film. This process may be repeated a preset number of times. The signal averaging time (i.e., the time during which the drum is rotated through a specified angle) may be preset to 100 milliseconds, one second, or ten seconds. By averaging a large number of signals, some average value signal may be detected on the photograph. The Electro-encephalographic Signal Averager consists of two primary sections: an electronic control system and a servomechanism. The electronic control portion provides all necessary timing signals to permit presetting of the averaging time and the number of times cycling is to occur. It also furnishes appropriate control signals to the servomechanism. The servo assembly is approximated as a second order control system employing both position and velocity feedback. Using a high performance DC motor, a rise time of less than eight milliseconds and a drum rotation linearity of less than one percent was obtained.