558 Prelinunai'ij Accoiuit of a Wave-Tracer and Analyser. 



one, or ^^ hen driven by a four-pole synchronous motor. I£ 

 driven direct by a two-pole generator it would obtain the 

 2nd, 6th, JOih, and 14th components if such existed. 



It is built up of five castings of hard gun-metal, turned 

 inside and outside, insulated from the spindle by ebonite tubes 

 and from each other by mica. Two nuts screwed on the 

 spindle bolt the parts firmly together, and the hollow space 

 inside is filled w^ith an insulating compound that is poured 

 in hot. 



Fig. 4 is a photograph of the complete commutator, and 

 shows how the bi-ushes are mounted on a kind of squirrel- 

 cage wdth four bars, wdiich rotates on tubular extensions of 

 the bearings. 



The divided circle and tangent screw', by means of which 

 the brushes are rotated and their different positions deter- 

 mined, can also be seen. Carbon brushes are used, and they 

 are double-banked, two connected brushes being at opposite 

 ends of a diameter of the drum. This greatly lessens the risk 

 of loss of contact due to vibration. To the free end of the 

 spindle is attached a speed-counter, which is so arranged that 

 it desired it closes an electric circuit through a chronograph 

 every 50 revolutions, and so a continuous record of the speed 

 during an experiment can be kept. If great accuracy is not 

 desired, the speed-counter can be used with a stop-watch. 

 The smallest of the insulation-resistances measured between 

 brushes bearing on contiguous sections of the drum was 

 250 megohms, and it runs without perceptible vibration at 

 20U0 revolutions per minute. 



14. Examples of Wave- Analysis hy Photogo^apMc Method. — 

 Fig. 5 is a wave-form of current from rotary transformer 

 with 3 times its 3rd, 5 times its 5th, and 7 times its 7th 

 component, the latter jnst perceptible. 



The components in all photographs are similarly multiplied 

 by numbers equal to the order of the component, and are in 

 their correct positions as to phase relative to the first and to 

 each other. 



The fundamental harmonic of the w^ave can obviously be 

 determined very approximately by subtracting from the full 

 wave-form its different components. 



As an illustration of the power of the method and the 

 w^orking of the instrument I may refer to fig. 6, obtained 

 from a 2000 volt-150 KW. Parsons generator at 45 ampere 

 load, partly inductive and partly a water-resistance. 



With the wave-tracer w^e can obviously obtain all the 

 periodic quantities involved in the action of a transformer, 

 both in magnitude and in correct relative position as to 



