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BELL SYSTEM TECHNICAL JOURNAL 



spring Ai, which limits the testing pressure appHed to the soldered 

 joint. 



If the length of pin is within limits, the electrical circuit remains 

 open and the coil passes on to the next test. If it is too short, the 

 circuit is closed through lever Bz coming in contact with B^, and if too 

 long the contact is made with B^. 



If the soldered joint fails, the effect is the same as a short pin. In 

 either case the tripping magnet operates and at the next position of 



Fig. 8 



the disc the defective part is released and drops into the proper 

 container. 



For testing the electrical resistance, contact is made with the coil 

 terminals by the gaging machine and the resistance measurement 

 proper is made by means of the apparatus shown in Figs. 7 and 8, 

 which is essentially two Wheatstone resistance bridges, one for checking 

 the resistance of the coil against a low limit and the other against a 

 high limit. The galvanometers G, for indicating the balance of the 

 bridges, each have a small rectangular, delicately pivoted coil which 

 rotates between the pole piece of a strong magnet. The end of a long 

 pointer attached to the coil is broadened out and contains a narrow 

 slot which, in connection with a fixed slot, forms a shutter that passes 

 or intercepts (depending on the position of the coil) a beam of light 

 from a small lamp in the hood L passing to the photo-electric cell M. 



The photo-electric cell is connected in the circuit of a vacuum tube 

 amplifier, the tubes of which are shown at V. The position of the 

 small shutter on the galvanometer needle is determined by the relative 



