ENSURING LIABILITY

Hawke's Bay Tribune, Volume XXII, Issue 148, 8 June 1932, Page 10

ENSURING LIABILITY

TESTS FOR COMPONENTS. A receiving set must not only give the perfromance for which it was designed, but must also be freed from the possibility of breakdown if it is to keep its manufacturer in business. For these reasons the rigid testing which is necessary for the successful commercial production of modern single-control receivers is virtually divided into two parts, one of which deals with the components with a view to ascertaining whether they can stand up to their job and the other of which proves that the finished article can supply the necessary selectivity, sensitivity, and quality. A humble, out by no means the least important, component in a modern set is enamel wire, because many yards of ti are used in the tuning coils, power transformer, windings, chokes, speaker field coils, and like components. Even slight imperfections may lead to serious trouble. The enamel must be perfectly continuous and of the designed uniform thickness, while it must have the ability to resist the corrosive or solvent actions of other materials with which it may come in contact in use or in the course of manufacture. Another property which must be observed is the ability of the enamel to stand up to the bending to which it is necessarily subjected during winding processes, and to the temperature which it has to endure in its final position. Other insulating materials which are employed must also endure the specific atmospheric temperature, and voltage conditions without any alteration of characteristic. In practice the wire and in the insulating materials when combined in the form of windings for transformers and the like are generally subjected to a comprehensive series of tests, the nature of which varies according to the ideas of the individual manufacturer. Before the winding is incorporated in its transformer the voltage induced in it. by a magnetic field of known character may be accurately measured as a check for the correct number of turns and to ascertain whether any of them are short-circuited. If required, shortcircuiting may be more accurately tested by including the coil in a circuit of a valve which is oscillating at low frequencies. By adjusting this valve so that it is only just oscillating the existence of short-circuited turns will he indicated by a cessation of the oscillation. For power transformers the various windings in all possible combinations are generally subjected tu predeteruan-

ed voltages of several times their normal operating voltage, whereupon any breakdown or weakness between windings is indicated. The possiblity of a breakdown of insulation occurring in use is usually checked by the application of a high-voltage direct current, while overheating tests are also applied. These are only a few of the points which are watched apart from the checking of the completed receiver, for which ingenious devices for carrying out the work accurately and rapidly, but with reasonable economy, have been thought out.