PLATED QUARTZ CRYSTAL UNITS 



235 



2. Supports for holding the crystal plate in its mount, and 



3. A sealed outer case having the necessary terminals, and provisions for 

 incorporating the unit electrically and mechanically into the apparatus. 



Two distinct types of crystal units have been evolved, one embodying 

 the use of pressure pins or anvils for supporting and holding the crystal 

 plate and the other involving the suspension of the cr}-stal plate by means 

 of fine wires.- These designs are known, respectively, as the Pressure T^'pe 

 and Wire Supported Type, and will be discussed later under these headings. 

 However, there are several details of fabrication common to both types 

 which can best be discussed at this point. 



Fig. 13.1 — Pressure-type holders. 



Irrespective of the type of mounting, realization of the desired perform- 

 ance in a crystal unit depends to a considerable extent on the processing of 

 the quartz plate itself. Previous articles^' ^ have brought out the signifi- 

 cance of such factors as the precision of angular orientation and linear 

 dimensions on the fundamental characteristics of the plate. The plate 

 must also be virtually free of impurities or imperfections.^ In the prepara- 

 tion of a quartz plate it must be lapped using increasingly finer abrasive 

 materials until the final dimensions are reached. Depending upon the type 

 of crystal unit. No. 400, No. 600 carborundum or finer abrasives are now 



* A. W. Ziegler, Patent 2,275,122, March 3, 1942. 



' "The Use of X-Rays for Determining the Orientation of Quartz Crystals", W. L. 

 Bond and E. J. Armstrong, B.S.T.J., Vol. XXTI, Oct. 1943. 



■> "Raw Quartz, Its Imperfections and Inspection," G. W. VVillard, B.S.T.J., Vol. 

 XXII, Oct. 1943. 



