Oscillographs for Recording Transient Phenomena^ 



By W. A. HARRISON 



In this paper, oscillographs developed for recording transient phenomena 

 are described which obtain automatically records of amplitude, wave form, 

 frequency, duration, and time of any electrical disturbance for which they 

 are adapted. Two instruments are described for recording very short or 

 very long transients: these may be used in combination. At power frequen- 

 cies satisfactory records may be made on film or sensitized paper with a 

 two-watt lamp. The instruments and their performance are illustrated by 

 photographs and oscillograms. 



OSCILLOGRAPHS are described which were developed primarily 

 for recording transient phenomena of which the time of occur- 

 rence is neither known nor subject to control. The specific apparatus 

 described was designed primarily for recording transient inductive 

 disturbances in communication lines from neighboring power circuits. 

 When the design of this apparatus was begun, there was no satisfactory 

 way for determining the duration, frequency or wave form of such 

 disturbances, although apparatus was available by means of which the 

 approximate magnitude of such transients could be determined, and, 

 by constant supervision, the time of their occurrence. It was with 

 the idea of determining part or all of these factors automatically in a 

 single record that the oscillographs to be described were developed. 



Transients in general may be of various types. They may have 

 components in a large range of frequencies, they may occur in a large 

 range of amplitudes and may be very long or very short or inter- 

 mittent. Attention was directed toward recording devices which 

 would obtain records of any disturbances in excess of a predetermined 

 magnitude regardless of the time of occurrence. For practical reasons 

 it was necessary also to give attention to the cost of operation, the 

 power consumed, and the amount of servicing in operation. 



To meet these requirements two somewhat different types of oscillo- 

 graph were developed. One is capable of making records of short 

 duration having uniform resolution throughout. By its use the wave 

 shape of the first half cycle of a transient is recorded as clearly as 

 that of any subsequent wave. The other instrument makes long con- 

 tinuous records and may be arranged to record a disturbance of any 

 reasonable duration. The former instrument makes records in polar 

 coordinates on a sheet of film rotating in its plane and will be called 

 a "polar oscillograph." The latter records in rectangular coordinates 



1 Presented at the Regional Meeting of the Middle Eastern District of the A. I. E. 

 E. at Cincinnati, Ohio, March 20-22, 1929. 



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