.■I\ El.f.CTRICAL VREQUF.NCY ANALYZER ?^2i 



uiulor tlu- \om\ condition only, thus indicating that it is due to an 

 / R drop at the brush contacts or to an c. in. f. de\'i'lopc<i in the short- 

 circuited coil with the brush off the magnetic neutral. 



The very small irreRularilies on the record shown particularly 

 between peaks above "joO cntIcs on the load record are probabK- due 

 to slight chattering of llie l)rushes. 



It is of interest to note that the .sfi cailetl frequenc>' of comnuita- 

 tioii does not appear in either of the records. I'or this machine tiiis 

 frequency at no load is approximately 346 cycles per second. 



From these records it is possible to determine the r. ni. s. value 

 of the alternating voltage at any frequency of interest. This is 

 computed from a knowledge of the circuit constants and analyzer 

 impedance. We thus obtain for the 550-cycle peak (Fig. 17) a value 

 of O.S \dlts and for the 60-c>'clc peak a value of 1.1 volts. 



In general the records taken by means of the anaK^zer on this 

 commutating machine, confirm quantitatively the well known fact 

 that such machines may give ri.sc to frequencies in ilie audible range. 

 Consideration of the records indicates that llicsc fretiucncies nui>' 

 be divided into two classes: F"irst, those pertaining to and controlled 

 by design, and second, those caused and controlleil b\- the plnsical 

 condition of the machine at any particular time. It is also interest- 

 ing to note that the driving motor may produce an appreciable effect, 

 particularly unfler the no-load condition. 



Si MMARV 



In the abo\e paper there has been gi\en a short statement of the 

 theory and construction of an automatic, recording, electrical fre- 

 quency analyzer, together with illustrations shf)wing its use and 

 limitations in various fields. 



This apparatus has been found \er\- useful in liie laboratory in 

 .the investigation of many different types of problems chiefly because 

 of the speed with which records can be made and harmonic analyses 

 obtained without computation. 



In conclusion the authors wish to express their appreciation to 

 Mr. C. E. Lane and Mr. C. E. Dean, of the Western F^lectric Com- 

 pany, Inc., for their assistance in the building of this machine and 

 the preparation of this paper. 



