RELAY MEASrinXC IHill PMEXT 21 



parts of tlu' slructui'c conti'ol the li.!;ht t'alliii.ii on the cell, whose output 

 can then be oonxerted so as to read (hrectly as (hsplacenient . 'Hie di.s- 

 phieement data may then be (HiTerentialed as a function of time, in 

 electrical differentiating circuits, to give very accurate measurements of 

 velocity. A complete description of this method, originally due to E. L. 

 Xorton, has been published by M. A. Logan.*' As a result of the accuracy 

 and convenience of this method, it has recently been used extensively 

 in relay studies correlating the amount of contact chatter with armature 

 \-elocity. 



The motion of parts may also be observed with various forms of trans- 

 ducers. One which is now finding application in telephone relay studies 

 is a type of electrostatic gauge, measuring armature displacement by 

 the changes in capacity between it and a fixed electrode. The entire 

 scheme is to be described by T. E. Davis and A. L. Blaha in a forth- 

 coming issue. 



Some relay motions need to be studied in three dimensions. Then the 

 high-speed motion picture gives best results. By photographing at up to 

 5,000 frames per second, and viewing at about 20 frames, a time mag- 

 nification of 250 to 1 can be gained. If need be, such pictures may be 

 scaled off to give displacement-time information, a somewhat tedious 

 task. A recent study of the effect of dropping in shipment gives a strik- 

 ing picture of the utiUty of the method Fig. 15 gives views, photographed 

 at 3,000 frames per second, of an AF relay as its mounting plate strikes 

 a concrete block at the end of a six inch fall. Severe distortion, followed 

 by recovery of the parts to normal, may be seen. With such information, 

 relay designers can plan parts to stand the service stresses, and form a 

 clear judgment of the margin of reliability built into the structure, 



CONCLUSION 



Although the relay is one of the oldest de^'ices in the telephone busi- 

 ness, many features of its operation are still imperfectly understood, even 

 today. The number and complexity of the continuing technical problems 

 may be judged from the other articles in this issue, on representative 

 relay subjects. As improved relay operation becomes ever more important 

 in the telephone system, the analytical and measuring technology for 

 these devices must progress, in parallel. Some of the typical measuring 

 equipment, as needed for modern relay design, has been described in 

 this article. 



REFERENCES 



1. R. L. Peelv, Jr., Mea-suring the Pull of Relays, Bell Lab. Record, .June, 1953. 



2. T. E. Davis, Measuring the Load-Displacement in Relays, Bell Lai). Record, 



June, 1953. 



