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Foreword.—This paper is an account of work conducted at the Signal Corps Engineering Laboratories which pertains to the development of the Standard Cycle for Moisture Resistance Testing of Component Parts for use in electronic equipment The recent increasing interest in reliability and tropical tests has led the author to believe that his experiences in this field may to some extent be a contribution to the state of the art. In the latter part of 1943, the extent of failures of communication equipment occurring in the tropics, where vital phases of the war were being fought, had become a serious concern to the Signal Corps Engineering Laboratories. Many types of failures, such as in Fig. 1, including corrosion, loss of set sensitivity, inoperation and others were attributed to the severe tropical conditions being encountered. The laboratories, located at Fort Monmouth, N. J., are responsible for the research and development of all communication equipment for the Department of the Army. As quick action was taken to improve the performance of equipment in the tropics, many protective techniques, such as the use of hermetic seals, coating materials, impregnants, etc., were being developed and used. In order to insure performance, some variety of either a humidity test, immersion, or “dunk” cycle or a salt spray exposure would usually be included in the applicable specification. In a short time, the types of tropical tests being specified were so diverse and numerous that it was necessary to standardize quickly on a test procedure. The many varieties of test procedures created a confusion as to the significance of results, since many were founded on an incomplete knowledge of tropical field conditions. In some specifications, two equipments would require that the same transformers should meet two different requirements although intended for the same field environments. It then became impossible to compare the results of tests of various subcontractors' parts or to correlate either result with field reports. The increased procurement during the war created an immense demand for humidity test facilities, and the resulting backlog made it necessary to standardize on a single test procedure so that a large work load could be handled efficiently and expeditiously.
Lascaro, Charles P.
Assistant Chief, Squier Signal Laboratory, Fort Monmouth, N. J.