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BELL SYSTEM TECHNICAL JOURNAL 



swinging contacts between the wires of each pair under test and 

 simultaneously to record the velocity and direction of the wind. 



To obtain an idea of the nature of a contact, oscillograph studies 

 were conducted at the outset. The oscillograms (Fig. 3) are repre- 



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V 



V V V V V V 



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Iff^rm^w^ 



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Fig. 3 — Oscillograms of swinging wire contacts. 



sentative of the results obtained. The timing wave has a frequency 

 of 60 cycles. When swinging into contact, it appears that the wires 

 scrape and chatter as evidenced by the rapid variations in the current 

 flow. It was found in these oscillograph studies that during a single 

 contact the resistance might vary from zero to 50,000 ohms while in 

 another case the variation might be from zero to 5,000 ohms. The 

 duration of a contact varied approximately from 0.004 to 0.230 second. 



