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BELL SYSTEM TECHNICAL JOURNAL 



twins left after cutting electrical twins apart) may be isolated or removed in 

 an intermediate or late stage of processing, where they are detected by the 

 etch technique. Commonly the final rejection of material twinned in either 

 way is delayed until after the final blanks are cut out. These may be 

 etched and examined by reflection, one at a time under a spot lamp, and 

 those showing twinning (and other imperfections) sorted out and rejected. 

 Another possible method of rejecting twinning which is of sufficient 

 amount to be harmful is by making electrical tests on the finished (or semi- 

 finished) plates, at which time those plates failing to meet the electrical tests 

 for any reason (including twinning), are rejected. While this method of 

 rejection does not assure that twinning will be entirely absent from the 

 accepted plates, neither does any other method assure complete absence of 

 twinning. Further, except for imperfections which may affect the useful 

 life of the plate, acceptance of finished oscillator plates is not illogically based 



upon their meeting the desired electrical operating characteristics, i.e., 

 frequency, temperature-coefficient, activity and internal damping (all de- 

 terminable by electrical tests) .-^ It does not appear that twinning will afifect 

 the useful life of the plate. Its effect upon the electrical operating charac- 

 teristics of the plate depend upon many factors. 



An important factor regarding twinning in the finished plate is that optical 

 twinning introduces a less important variation in the physical properties of 

 the plate than does electrical twinning. Thus, in the case of optical twinning 

 alone, both portions of the plate are of the same sense of cut, though still 

 being of opposite electrical sense. This may be understood from an ex- 

 amination of Fig. 5.4, the second and third views taken together represent 

 optical twinning. In the case of electrical twinning the two portions of the 



2^ With filter plates additional operating characteristics must be met. The ratio of 

 capacities (see Chap. I, Appendix A.3) is greatly affected by the opposed electrical sense 

 of twinning. 



