PERFECCIONAMIENTOS EN LOS RECEPTORES DIFERENCIALES.

摘要

This invention relates to reference systems of the type used for surveying railroad track in which a light beam transmitter, a beam receiver spaced therefrom and a railroad condition sensor having a single edged shadow board is located therebetween. The invention contemplates positioning at least two photo-cells in the receiver physically closely spaced apart in the direction of shadow board motion. The outputs from the photo-electric cells are electrically connected in a differential configuration so that a command signal is generated to stop shadow board movement into the transmitted beam when the shadow board reaches a datum position at which point the distribution of the transmitted light on the photo-cells will have achieved a predetermined difference. In one aspect of the invention a deadband producing photo-cell is provided in the receiver and located physically closely spaced apart from the other two photo-cells in the direction of the shadow board motion and inwardly of the edge thereof when it is in datum position. The deadband producing photo-cell is electrically connected to generate a command signal to commence shadow board movement into the beam when the deadband producing photo-electric cell is exposed by a predetermined amount to the transmitted beam.