. The Bell System technical journal . ualization is desired only to a frequency a littlebelow Fo, and if maximum sensitivity is not essential, it is sufficientto shunt the galvanometer with a suitable resistance. Four ohms isabout the right value for the instrument under discussion, and gives adeflection vs. frequency curve as shown in Fig. 5. There is a decidedpeak of sensitivity at ^Fq with the result that when a current with a i 200O I 1 REACTANCE NEAR FUNDAMENTAL RESONANCE FREQUENCY —■ /- / \ 2400 2500 2600 2700 2800 2900 3000 3100 3200 3300FREQUENCY IN CYCLES PER SECOND 3400 3500 3600 Fig
. The Bell System technical journal . ualization is desired only to a frequency a littlebelow Fo, and if maximum sensitivity is not essential, it is sufficientto shunt the galvanometer with a suitable resistance. Four ohms isabout the right value for the instrument under discussion, and gives adeflection vs. frequency curve as shown in Fig. 5. There is a decidedpeak of sensitivity at ^Fq with the result that when a current with a i 200O I 1 REACTANCE NEAR FUNDAMENTAL RESONANCE FREQUENCY —■ /- / \ 2400 2500 2600 2700 2800 2900 3000 3100 3200 3300FREQUENCY IN CYCLES PER SECOND 3400 3500 3600 Fig. 4—Variation in reactance near fundamental resonance frequency with imageamplitude constant at 2 mm., peak to peak. AN OSCILLOGRAPH FOR TEN THOUSAND CYCLES 79 square wave front is applied, a weak damped oscillation containingabout one cycle of Fq and many cycles of ZFq will be superposed on thesquare wave record, as has already been reported by Professor H. The effect of the third partial oscillation is usually of. 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000 II000 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 stringimage, and its effect is noticeable principally as a slight blurring ofthe trace. This method of resistance-shunt damping, used with the earlier formof 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. ^ An inductance in series with a capacitance, which resonatesit to Fq, and a suitable resistance are sufficient The characteristicsof a string shunted with such an equalizing element, in which for con-venience the capacitance was made considerably less than the optimumvalue, is shown in
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