Photo-electric Control in Industry


    AT the Nottingham meeting of the British Association, Mr. A. L. Whiteley contributed to Section A a paper on photo-electric control in industry. The photo-electric cell provides greater rapidity of action and a higher sensitivity than other light-sensitive devices. The greatest field for it is the talking picture industry, but this does not come under the subject of his paper. In industry the cells are usually made in standard sets called photo-electric relays, containing an amplifier circuit and a small contactor capable of making or breaking 15 amperes. An obvious application of this unit is counting objects on a conveyor belt or vehicles passing on a road. It can easily be used to make the pointer of an instrument actuate an external circuit on reaching a predetermined scale reading. Applications of this nature include automatic weighing of mass-produced parts and automatic termination of operations on high precision grinders when a mechanical gauge records that a certain diameter of the part operated on has been reached. It is also used to control street lighting according to variations in the intensity of the light. In many types of automatic wrapping and bag-making machines a continuous preprinted web of paper or "Cellophane" is fed to the machine at a high speed. It is necessary that positional relationship between the printed matter and the fold or cut be maintained. This is done by the response of the printed matter itself. The system is used abroad to maintain 'register' between the design and the perforations of postage stamps. It can be applied to record the intensity of the smoke corning from a chimney and the temperature of strip steel as it comes from the hot rolls of a rolling mill.

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    Photo-electric Control in Industry. Nature 140, 927 (1937).

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