On Electronic Timer for Photographic and Automatic Control Applications

Abstract

Correct time intervals ranging from 0.1 second to 1 minute for operating photographic printing lamps and other control apparatus are provided by a simple device using an electro-nic tube and a delay circuit. By checking up to 0.001 second with an electronic counter of the accuracy of ±0.0001 second, the device showed an accuracy very much higher than that of customary timers. The principle of operation is based upon the change of plate current, which operates a relay, in accordance with the change of the charging time, i.e. the delay time, of capacitor through an adjustable resistance in C-r delay circuit. A noticeable feature is that as it has a stabilizing tube each in the B electric power supply and the bias circuit, the current characteristic varies according as which one of the two tubes is operated. We may, therefore, choose the one that suits the purpose. Thus, in face of fluctuating line voltage of say ±10%, error in timing can be made as small as ±1.0%.