QUARTZ CRYSTAL PLATES 



533 



maximum at the point wo' where it has zero coefficient, and then 

 decreases. As the frequency decreases the activity of this particular 

 mode decreases rapidly and finally the crystal "hops" frequency to 

 point C on the co" curve. From this point on the frequency with 



35.5 °C. 



710 712 714 



FREQUENCY KILOCYCLES 



Fig. 15 — The response-frequency spectra of a parallel cut crystal plate at different 

 temperatures illustrating the interchange of activity between the two frequencies 

 as the frequencies of the two modes of vibration pass through a coincident value. 



Length of plate along optic (Z) axis = 47 mm. 



Width along electric {X) axis = 19.35 mm. 



Thickness along mechanical (F) axis = 2.75 mm. 



temperature increases, for this frequency has a positive temperature 

 coefficient in this region. 



