SOLDERLESS WRAPPED CONNECTIONS 



PART III 



595 



3. Chill for two hours at 0°F. 



4. Heat for three hous at a temperature (175°C) which will relax the 

 stresses as much as will occur during the expected life at the normal 

 central office operating temperature. 



5. Expose the connection to a suitable agent which will discolor all 

 the non gas-tight area. 



6. Remeasure the resistance variation as in 2. 



7. Unwrap the wire and estimate the size of the gas-tight areas. 



Items 1 and 2 are intended to show whether initially there is the inti- 

 mate contact between wire and terminal demanded by the General 

 Requirement No. 1. At present, the multiple terminal banks on step-by- 

 step switches are connected together with a clinched solderless con- 

 nection. Based on experience with these connections, together with an 

 estimate of the noise produced (See appendix A) a resistance variation 

 in excess of 0.002 ohms is considered to indicate a poor connection. 

 Items 5 and 7 will show the existence of the gas-tight areas demanded by 

 General Requirement No, 2, and the size estimate from Item 7, the 

 area of contact demanded by General Requirement No. 4 can be evalu- 

 ated. Items 3 and 4 are intended to simulate most of the aging which 

 will take place during the life of the connection. It is believed, as de- 

 scribed earlier in this paper, that relaxation of internal stress is the 

 chief factor in the aging of these connections. The chill at 0°F puts the 

 maximum initial stress in the wire by shrinking it at extreme operating 



MILLIAMMETER 



FULL SCALE 



100 MA 



MILLIVOLTMETER/^ 



FULL SCALE V 



7.5 MV V^ 



Fig. 1 — Test set for measuring resistance of solderless connection. 

 Test Procedure 



(1) With Ri set at "a" and switch SW closed, adjust R2 so that the millivolt- 

 meter reads 25 microvolts with Rx open. 



(2) If millivoltmeter returns to zero with test connection across Rx , no barrier 

 film is indicated and therefore connection is closed. 



(3) All resistance measurements are made with R^ set to give 100 milliamperes 

 through Rx . Then Rx = millivolts/0.100. 



(4) A variation of not more than 2 milliohms as the connection is moved or 

 disturbed indicates a stable connection. 



