ACCELERATION EFFECTS ON ELECTRON TUBES 



1209 



cause phase distortion between the impressed and recorded frequency 

 components takes place. Fig. 3* graphically illustrates this relation. This 



figure shows that l — j would have to be made approximately 0.5 in order 



to have a phase angle proportional to the impressed frequencies, i.e., to 

 obtain a true recorded pattern of the disturbance. Damping is generally 

 not employed in accelerometers built to duplicate the size and weight of 

 electron tubes due to constructional difficulties. The useful frequency 

 limit of these devices is often not governed by the resonant frequencies 

 of the active elements but by the lowest resonant frequency of their 

 housing structure. 



As mentioned previously, the active elements of these light weight 

 transducers can be employed in various ways. The first models which 

 were developed a few years ago made use of the elements in compression, 

 following the practice of their predecessors, or: the relatively heavy and 

 large quartz crystal accelerometers. A working model of a compression 

 unit is shown in Fig. 4(a). Although this type of unit can be constructed 

 to have a very wide useful frequency range (high resonant frequencies), 

 it possesses two disadvantages: its internal capacity is rather low, and 

 it has poor directional sensitivity. Its sensitivity decreases to roughly 



180 



OJ 



cr 

 o 



" 90 



45 



0.5 



2.0 



2.5 



3.0 



1.0 1.5 



Fig. 3 — Phase angle between force and displacement as a function of the 

 forcing frequency for two values of damping. 



