OPEN-CONTACT PERFORMANCE OF TWIN CONTACTS 1383 



plate with the fibres. The pressing force was the same as that used in the 

 subsequent operation of the contacts. The contacts were then operated 

 at four operations per second in a sealed compartment. After each 

 closure a checking circuit using 48 volts, and a maximum current of 

 0.50 amp., checked the continuity in the contacts. When the open was 

 cleared the unit automatically stopped and the corresponding number of 

 operations was obtained from a counter. The maximum number of opera- 

 tions allowed for each run was 2,000. For one set of operating conditions, 

 it was necessary to repeat the above for at least 150 times before a repre- 

 sentative clearing distribution was obtained. 



Results 



Effect of Mdpe: Fig. 5 shows the results obtained for a range of wipes 

 between 0.006 and 0.025 cm at a constant force of 10 grams. As expected, 

 the clearing rate was higher for larger wipes. 



Effect of force: Fig. 6 was obtained at a constant Avipe of 0.006 cm and 

 a set of forces between 5 and 80 grams. Large forces gave higher clearing 

 rates. The effect of changing the force, however, is not as significant as 

 that of changing the wipe. 



As outlined in the preceding introduction, the above data was replotted 

 as fraction clearing / versus Nw"F'^. The results are shown in Fig. 7 with 

 a = 3 and 6 = 1.0. As indicated, the pomts converged to a single average 

 line with comparatively small spread.* This shows that, at least for the 

 range covered, the change in clearing rate obtained by changing the wipe 

 say by a factor of two can also be obtained by changing the force by a 

 factor of 8. 



To determine the persistency (1 — /„), one may choose an arbitrary 

 number of operations for defining it. If 2,000 operations is chosen, one 

 may determine from the above data the fraction, (1 — /2,ooo), that will 

 persist to beyond 2,000 operations. This was done and the results are 

 plotted in Fig. 8 as (1 — /2,ooo) versus F^'^w. This suggests the follow- 

 ing relation: 



— /2,ooo) = e (11) 



where F is in grams and w in cms. This expression allows the determina- 

 tion of the effects of force and wipe on the performance of twin contacts 

 by substituting in Equations 7' through 10. Similarly the average number 

 of operations n, used in the above equations, may be obtained. This may 



* This same convergence was obtained, but not presented here, by plotting / 

 versus NF at constant iv and / versus Nw^ at constant F. 



