ACCELERATION EFFECTS ON ELECTRON TUBES 1205 



ACCELEROMETERS AND ASSOCIATED INSTRUMENTATION 



Instrumentation employed for measuring accelerations depends largely 

 on the frequency range of the disturbances to be recorded, which, for 

 vacuum tube applications, covers approximately the audio spectrum. 



In practically all cases, electronic recording equipment is used because 

 of its high degree of flexibility. Its basic components consist of (a) a 

 mechanical-electrical transducer which translates mechanical distur- 

 bances into proportional electrical potentials, (b) an electronic amplifier 

 to step up the voltage output of the transducer to desired levels, and (c) 

 an indicating instrument, usually a cathode ray oscilloscope, for obser- 

 vations of the disturbances. 



Accelerometers 



Although several types of mechanical-electrical transducers or pick- 

 ups are in existence,^ it has been found that the self generating types em- 

 ploying materials such as quartz or ferro electric crystals, are most useful 

 since they can be constructed so that their output is directly proportional 

 to acceleration over a large frequency range. Velocity and displacement 

 indicating instruments are sometimes used for low frequency work; by 

 suitable differentation their output signal will be proportional to acceler- 

 ation. 



An accelerometer must have the following fundamental properties: 



(a) the signal produced must be proportional to the accelerations to 

 be measured. 



(b) its calibration must be stable and unaffected by humidity and 

 temperature changes encountered. 



(c) its mechanical strength has to be adequate to withstand the accel- 

 eration stresses to which it is subjected. 



(d) its weight must be sufficiently low so that the disturbance patterns 

 are not modified by loading. 



(e) its sensitivity (voltage output/g) and useful frequency range must 

 be sufficiently high to cover acceleration magnitudes and frequency com- 

 Donents to be recorded. 



A number of piezoelectric materials are available and have been em- 

 ployed in various electro-mechanical transducers. The development of 

 practical light-weight transducers has been made possible by the use of 

 some of the relatively new ferro-electric ceramics. By proper compound- 

 ing, firing and poling, these materials can be made to have very high 

 sensitivity and good life stability. Other advantages are their high dielec- 

 tric values, good mechanical strength and relative insensitivity to usually 



