1110 
MONITORING 
of 50 ohms and shunt capacity of 5.83 pF. For 
this crystal the manufacturer was more specific 
in that he shipped measured values along with 
the crystal. 
From these plots one must conclude that the 
crystal of curve B more nearly follows the ex- 
pected impedance curve as predicted by theory 
than does the crystal of curve A. One might 
have been able to design a circuit using a crystal 
equivalent circuit and the manufacturer's 
sketchy data for crystal B, but would have had 
a difficult time designing a circuit by using the 
3 pieces of information supplied with crystal 
A. There were other crystals received from 
manufacturer B that did not agree with the ex- 
pected curve as well as that shown, but this 
particular crystal was picked to indicate that 
some crystals do measure as theory predicts. 
One special problem in designing low energy 
circuits is that the drive level of the crystal 
must be considered. Normally, the maximum 
drive level is of interest and must not be ex- 
ceeded or the crystal will be damaged, but for 
low energy circuits, as are often used in bio- 
