252 



BELL SYSTEM TECHNICAL JOURNAL 



13.46 Mounting the Crystal Plate 



After the suspension wires are affixed to the plate, they are then bent to 

 serve as springs and to permit soldering into the cages as illustrated in 

 Fig. 13.2. Two different types of springs are used, one of them involving 

 one bend and the other two. The direction of the bends and the distances 

 between them have been worked out so that the crystal will be displaced 

 to about the same extent in all three directions for equal forces. The 

 cages are of simple construction being made up of mica stampings and 

 metal rods. The assembly of these parts is performed by welding little 



AMPLITUDE OF WIRE VIBRATION 



VERSUS 



NUMBER OF COMPLETE EXCURSIONS FOR .0063 INCH DIA. PH. BR WIRE 



10* 10' 10' 10° 



NUMBER OF COMPLETE EXCURSIONS 



Fig. 13.10 — Characteristic performance of phosphor-bronze spring wires. 



eyelets, which are staked into the micas, to the rods. In the structures 

 shown, the inside micas are provided with rectangular slots which limit the 

 sidewise movement of the crystal plate from 25 to 30 mils. The end micas 

 are spaced so as to limit the movement of the plate in the lengthwise direc- 

 tion by the same amount. Aside from being used as parts of the cage, the 

 micas therefore serve as "bumpers" to prevent excessive displacement, and 

 possible breakage of the wires or plate if the crystal units are subject to 

 extreme vibration or shock. Figure 13.10 is an experimental curve showing 

 the minimum number of excursions made by wire-mounted crystal plates 

 vibrated at different amplitudes before wire failure occurs for 6.3 mil phos- 

 phor bronze spring wires with single bends. On the basis of these data, the 



