Abstract :
This paper describes the behaviour of Barrier Layer Photo electric cells in A.C. circuits and it is shown that whilst they behave as rectifiers in darkness they act as non-linear conductors to current in both directions when exposed to light. This change from uni-directional to duo-directional conductivity is used directly without amplifier valves, for operating relays in industrial devices used for switching, counting, grading and other operations. Used in this way, i.e. as a relay valve, the cell is some 300 times more sensitive than when used, as hitherto, as a detector. A further advantage of this novel method is that the cell may be small and can, if necessary, be mounted at some distance from the associated electrical equipment, thus permitting the cell to be used in places unsuitable for present equipment. If the cell is operated from the same A.C. supply as the lamp which illuminates it, a very high degree of electrical stability may be obtained. The paper ends with descriptions of circuits required for various industrial applications and some suggestions for future developments are made.
