382 



BELL SYSTEM TECHNICAL JOURNAL 



Fig. 14. One of two polar oscillographs is connected in the circuit 

 being investigated so that it is in condition to record the first part of 

 any transient that should occur. A high-speed line-relay associated 

 with it is arranged to put in motion the sequence switch which takes 

 care of a number of operations consisting chiefly in starting the con- 

 tinuous-film oscillograph, in substituting the second polar oscillograph 

 for the first after a certain small time interval, and in operating the 

 camera shutters at the proper times. 



LINE RELAY 



^ 



LINE 



L 



n 



POLAR 



OSCILLOGRAPH 



NO. I 



<n CLOCK 



^ 



SEQUENCE 

 SWITCH 



n 



MOVIE 

 OSCILLOGRAPH 



POLAR 



OSCILLOGRAPH 



NO. 2 



& 



X 



Fig. 14 — Arrangement of oscillographs for recording any transient in a line. 

 Two polar oscillographs and one continuous-filni oscillograph with control equipment 

 and clocks are arranged so that a transient of any duration occurring at any time will 

 be recorded with a record of the time of occurrence. 



Used in this way the first polar oscillograph obtains a record, 

 having considerable resolution, of the first part of a transient while the 

 other oscillograph obtains a record of the complete transient with the 

 exception of the first few cycles which are, however, obtained on the 

 polar machine. The sequence switch is adjusted so that the continuous 

 oscillograph is put in operation before the polar machine stops recording 

 so that, with the two records, complete information of the disturbance 

 may be obtained. Two polar oscillographs are used in this way so 

 that, in case two transients occur close together, a record of one of 

 them will not be lost during the time required for reloading. The 

 sequence switch connects the line to the spare polar oscillograph 

 automatically and gives the operator ample time to make any necessary 

 adjustments on the remaining machine. The arrangement is sym- 

 metrical and either polar oscillograph may become the spare. 



An example of the record of a transient obtained with a polar and a 



