1204 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



specifically designed to minimize the effects of such distrubances. For a 

 rational design, it is, therefore, necessary to have some knowledge of the 

 nature of the disturbances likely to be encountered by tubes during their 

 service life. If one considers the numerous conditions under which elec- 

 tronic equipment is required to function, it becomes clear that the me- 

 chanical requirements are manifold indeed. Equipment applications can 

 be divided into three general groups, each one imposing in many cases 

 special requirements on tubes. These groups are: (a) stationary equip- 

 ment, such as central office telephone installations, home radio and tele- 

 vision receivers, etc., (b) mobile equipment used in land vehicles, ships 

 or airplanes, and (c) portable equipment. In many instances, military 

 equipments straddle above subdivisions and superimpose additional re- 

 quirements. It must be stressed, too, that pre-service conditions encount- 

 ered through handling and shipping must be taken into consideration, 

 since a tube is of no use to the customer until it is installed and operating. 



A knowledge of expected service conditions is not only useful in the 

 initial design stage but also aids the manufacturer in devising suitable 

 test gear to check the quality of the product at the factory. Although a 

 wealth of data has been collected on shocks and vibrations to which elec- 

 tronic equipments are subjected under actual service conditions, little 

 is known how these disturbances are altered by the mechanical structures 

 of the equipments before they reach the tubes. In general, the nature 

 and magnitude of mechanical disturbances can be expressed in terms of 

 acceleration, velocity, or displacement. Since electron tubes may respond 

 to a wide frequency range of vibrations, the most sensitive measure is 

 acceleration, which varies as the square of the frequency of the element 

 displacement. Velocity or displacement instruments are usually not suffi- 

 ciently sensitive to give a true record of disturbances in the higher modes 

 of vibration due to the small velocity and displacement values involved. 



The investigation of the nature of accelerations at tube sockets offers 

 special problems. The accelerometers must approximate the weights of 

 the tubes used in the respective sockets so that the disturbances are not 

 modified by the substitution of acceleration pick-ups for the tubes. For 

 the same reason, the method of fastening the accelerometers in 

 the 80<!kets must duplicate that of the tubes, and since the accelerating 

 forces may act in several directions, the accelerometers must be capable 

 of exploring these various directions. Lightweight accelerometers meeting 

 the above reciuireraents have been developed recently. These instru- 

 ments are generally built to approximate the weight, weight distribution, 

 and shape of vacuum tul)e8. A more detailed description of these accelero- 

 meters and associated recording circuits is given in the following chapter. 



