Level detection device for enclosed tanks

A level detection system is disclosed that utilizes backscattered radiation in which a radiation source is vertically arranged between two radiation detectors along the exterior of a tank, the system automatically moving up or down along the height of the tank in response to radiation received by the detectors to indicate the level of material within the tank. Variations in wall thickness of the tank are automatically compensated for by comparing the electronic signals produced by the two detectors and using the differential signal to drive the system