QUARTZ CRYSTAL PLATES 



527 



Temperature Coefficient as Function of Dimensions 

 AND Temperature 



As mentioned above, when the temperature coefficients of these 

 parallel cut crystals were studied it was found that there was con- 

 siderable variation between plates having the same thickness but 

 slightly different areas, and the temperature coefficient of a given 

 plate was found to be a function of the temperature. • To illustrate 

 this last point a typical frequency-temperature curve for a parallel 



1.07 



1.03 

 1.02 

 1. 01 



0.99 

 0.98 



0.96 



13 14 15 16 17 



WIDTH ALONG ELECTRIC AXIS MM. 



Fig. 10 — The wave-lengths at which a parallel cut crystal will operate in an 

 oscillator circuit as its width (the dimension along the electric axis) is progressively 

 reduced, the other dimensions being fixed. 



Xo = 153 X thickness. 



Thickness along mechanical axis = 1.64 mm. 



Length along optic axis = 54.8 mm. 



cut crystal is shown in Fig. 11. It will be noted that the frequency 

 increase is linear until a given temperature is reached, at which point 

 the curve flattens off and then begins to reverse. Just beyond the 

 point of reversal the frequency jumps to a new value and, if the 

 curve is continued, the frequency increases again at the same rate as 

 originally. This type of frequency-temperature curve is common to a 

 large percentage of parallel cut crystals, the only difference being the 

 width of the flat part of the curve and the temperature at which the 

 discontinuity occurs. 



