ACCELERATION EFFECTS ON ELECTRON TUBES 



1223 



pendulum is allowed to swing under the action of gravity before the 

 hammer strikes the table. The forward motion of the table produced by 

 the impact is arrested by two shock absorbers. 



The impact of the hammer on the anvil of the table produces an 

 abrupt velocity change of the table and excites table resonances, both 

 horizontally and vertically. Because of the structure of the table a very 

 complex acceleration wave form results. In general the accelerations for 

 a given hammer swing vary over the table surface. It is for this reason 

 that, in testing procedures, the position of the tubes on the table and 

 their method of clamping are well defined; and since the acceleration 

 wave shape is the sum of many vibratory frequencies rather than a single 

 shock pulse, the severity of the test is expressed by the angle of hammer 

 swing instead of a shock magnitude and duration. Although some uni- 

 formity in performance is attained by rigid standardization of the struc- 

 ture of the machines and the above mentioned positioning of the tubes, 

 minute differences in these parameters may produce sufficient variations 

 in shock output to reflect on test results. Acceleration-time traces of 

 shocks measured in the shock direction by an accelerometer fastened near 

 the anvil of the table and a second accelerometer clamped to the center 

 of the table, are shown in Figs. 14 and 15. The records were simultane- 

 ously taken through 10,000-cycle low pass filters. Even though the 

 recording of accelerations containing high frequencies of large amplitudes 

 is, to some extent, a function of the measuring equipment, it is seen 

 that significant differences in output exist between the two points of 

 measurements. 



Fig. 11 — Acceleration-time pulse produced by MIL-E-IB bump tester. 



