DETERMINATION OF WAVE FORM 619 



engineering work. These devices are made self-registering. In 

 that shown in Fig. 384 the trace is recorded photographically. 2 



The necessary electrical connections are shown in Fig. 385. 

 Ki and K 2 are two rigidly connected contact wheels of ebonite. 



.--. ."-. ..-. 

 . ... .... .. 



.-A 



Curved, Electromotive Force Wave. Curve B, Current Wave. 

 Resonance of Fifteenth Harmonic 



FIG. 383. Wave form taken with Rosa curve tracer. 



Into the periphery of each wheel are set four brass blocks which 

 are placed 90 apart. Upon each wheel a brush and a collector 

 ring give permanent contact with all the blocks. Another 

 brush, resting on the periphery of the wheel, completes the 



Fio. :4. Synchronous commutator with continuously moving brushes, 

 for use in determining wave form. 



electrical connection as the blocks pass under it. The brushes 

 are so set that contact is made and broken at K 2 before Ki 

 closes. The contact wheels are driven by a synchronous motor, 

 which makes one revolution for four complete cycles of the 



