OSCILLOGRAPHS 383 



continuous-film oscillograph used together is shown in Fig. 18. The 

 polar oscillogram is similar to that shown in Fig. 8. It is obvious that 

 the continuous oscillograph began recording about five cycles after the 

 beginning of the transient while, of course, the polar oscillograph began 

 recording immediately. The long record, however, continues twenty- 

 five or thirty cycles beyond the end of the polar record and shows 

 the manner in which the transient ended. Space does not permit 

 of showing the clock that was photographed on the strip "record. 



When certain factors are known about the disturbances to be 

 recorded the arrangement may be somewhat simplified. If, for 

 example, it is known that any transient to be recorded will be of very 

 short duration, the continuous oscillograph need not be used. If, on 

 the other hand, it is known that the first cycle or two of the disturbance 

 will be of no importance in the record, the polar oscillograph may be 

 dispensed with. 



The continuous film type of oscillograph offers some decided ad- 

 vantages over the polar type in that a large number of records can be 

 made at one loading. Largely because of this it is possible to make the 

 oscillograph entirely automatic in operation, causing it to record, with- 

 out any attention whatever, all the transients in a circuit as they 

 occur, until the supply of film is exhausted. Such an oscillograph may 

 be left permanently connected into a circuit in which transients are 

 expected, and at the end of any period the film that has been advanced 

 into the "exposed" magazine will show on development records of the 

 magnitude, frequency, and wave form of the disturbances and of the 

 time of occurrence of each. 



For automatic operation of the oscillograph a sequence switch of 

 some sort must be used to insure that the various automatic operations 

 are performed in the proper sequence. In Fig. 15 a schematic drawing 

 illustrates the essential elements of such an arrangement. When 

 standing by, ready to record a transient, the motor on the oscillograph 

 is running but does not engage the film advancing mechanism because 

 the magnetic clutch is normally deenergized. On the arrival of a 

 transient the sequence of operation is as follows: 



The line-relay operates, and locks in operated position in virtue of 

 the bias current through the outer winding being removed by the 

 opening of the back contact. The lamp is lighted through the re- 

 sistance and condenser combination RC, and, at the same time, the 

 motor is engaged with the film driving mechanism through the magnetic 

 clutch. Since the vibrator is connected continuously to the line, re- 

 cording begins immediately. Relay SR operates at the same time that 

 the clutch is energized and starts the motor of the sequence switch 



