AN OSCILLOGRAPH FOR TEN THOUSAND CYCLES 



79 



square wave front is applied, a weak damped oscillation containing 

 about one cycle of Fq and many cycles of ZFq will be superposed on the 

 square wave record, as has already been reported by Professor H. B. 

 Williams.2 The effect of the third partial oscillation is usually of 



1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000 II 000 12 000 



FREQUENCY IN CYCLES PER SECOND 



Fig- 5 — Characteristics of instrument shunted with a resistance of 4 ohms. 



minor importance. Its amplitude is less than the width of the string 

 image, and its effect is noticeable principally as a slight blurring of 

 the trace. 



This method of resistance-shunt damping, used with the earlier form 

 of the rapid record oscillograph, gives very satisfactory character- 

 istics up to nearly Fq, but it does not develop maximum sensitivity, 

 which for its attainment requires an equalizing network with character- 

 istics inverse to those of the vibrating string, as described by J. T. 

 Irwin.^ An inductance in series with a capacitance, which resonates 

 it to Fq, and a suitable resistance are sufficient The characteristics 

 of a string shunted with such an equalizing element, in which for con- 

 venience the capacitance was made considerably less than the optimum 

 value, is shown in curve A of Fig. 6. It will be noticed that the de- 

 flection for a 10 ma. current has been increased from 0.11 inch, ob- 

 tained with resistance damping above, to about 0.36 inch — a sensi- 

 tivity better than three times as great 



This type of equalization alone, however, gives a sensitivity at 3Fo 

 nearly as great as that at T^o- Because of this there is a greater 3Fo 

 distortion with a resonant shunt when a square wave is impressed than 

 with the resistance shunt. The sensitivity at 2>Fq, however, may be 

 damped out by an additional shunt element, and when this is employed 

 the characteristics are as shown by curve B of Fig. 6. 



2 Jour. Optical Soc, September, 1926. 



3 U. S. Patent No. 1,324,054. 



