FROM CURRENT LITERATURE

NEW APPLICATIONS OF PHOTOCELLS IN PRODUCTION1

Photocells with an external photoelectric effect are finding ever wider application in various branches of American industry. One of the new applications is a device serving to control the cutting of paper, consisting of a photocell, two thyratrons, a small motor. Light from a small incandescent lamp, through four small lenses mounted on the motor shaft, falls on a roll of cut paper, on which there is a narrow dark guide line, and is diffusely reflected into the photocell. The circuit is adjusted so that as long as these light beams fall on the light surface of the paper, the thyratrons do not operate. But as soon as the beams fall on the guide line, the thyratrons switch on. This, by changing the voltage on the motor, leads to such a change in the position of the roll as is necessary for the continuation of a straight-line cut.

Another device, consisting of nine photocells, a thyratron, and a recording device, has recently become widespread at steel-rolling mills, where it is used to check steel sheets for the presence of holes. At a speed of the inspected steel sheet of \(240\ \text{m/min}\), this device makes it possible to detect and mark the location of holes of \(0.25\ \text{mm}\).

N. Khlebnikov, Moscow

Literature

1. Journ. Appl. Phys., 10, XII, 1939. ↩