OSCILLOGRAPHS 381 



inertia of the driven member it is rapidly accelerated to maximum 

 speed. Since this is a friction type of clutch, the acceleration is gradual 

 and does not submit the sprocket and film to shock as would a toothed 

 clutch. 



The delay in recording after the beginning of a disturbance depends 

 on the time of operation of the high-speed relay plus that of either the 

 clutch or the lamp, whichever is the longer. The relay requires only a 

 few thousandths of a second to operate and both the clutch and the 

 lamp may be adjusted to operate in less than one hundredth of a 

 second. With this apparatus, therefore, it is possible to record all of a 

 disturbance except that part which occurs during about the first 0.02 

 of a second. If desired, the lamp can be arranged to operate in con- 

 siderably less time than the clutch, in which case the first part of the 

 record will not be resolved but will indicate the amplitude of the 

 disturbance which is frequently the most desired information. In the 

 case of 25-cycle or 60-cycle disturbances the maximum of even the 

 first half cycle may be recorded in this manner. 



The film driving mechanism is arranged so that the film may be 

 advanced at any speed in a wide range, from a few inches per minute to 

 about a foot per second. This is accomplished by means of a set of 

 change gears and by changing the speed of the driving motor, or by 

 both in combination. 



As with the polar oscillograph, a camera is included for the purpose 

 of recording the time automatically on the oscillograph film. This 

 camera may be seen in Fig. 10. It is similar to that on the polar 

 oscillograph with the difference that only one prism is used. This has 

 the advantage, when recording is done on paper, that the image ob- 

 tained through a lens and a single reflection is not reversed. The 

 shutter is equipped with an automatic release that can be associated 

 with slow acting relays or a sequence switch to take care of photo- 

 graphing the clock on the right portion of the film. 



Operation 



There are a great many ways in which the oscillographs, described 

 above, may be used. An arrangement is described in which two polar 

 oscillographs and one continuous-film oscillograph have been used in 

 conjunction for studying transients which are likely to occur at any 

 time during long continuous periods. It was desired to determine the 

 magnitude with considerable accuracy and at the same time to de- 

 termine the time of occurrence, duration, frequency and wave form. 



The arrangement of oscillographs is shown diagrammatically in 



