OPEN-CONTACT PERFORMANCE OF TWIN CONTACTS 



1379 



of failure of twin contacts is also quite sensitive to initial contact con- 

 tamination. If, for example, So = 10~ , i.e., Hooo of the twin contacts 

 are permanently half-open to start with, and for the same numbers used 

 above and Ps = Ko^ equation 8 gives Pt = 1.1 X 10~ . This corresponds 

 to an 11 fold increase in twin-contact failures just due to an initial con- 

 tamination So of 0.1 per cent. This performance is also 1100 times worse 

 than the idealistic performance of Pt = P/ = 10~^\ 



By operation, the performance of twin contacts will exponentially 

 deteriorate according to equation 7. It will asymptotically approach a 

 constant rate of failure given by: 



(Pt)^ = Ps\l + 2/I/J + 2Ps 



1 -/o. 



(9) 



This is independent of the initial contamination So and is practically 

 reached in a number of operations: 



(nth = 3/(P.(3 - 2/J) (10) 



The worst performance of twin contacts is obtained when f„ = 0, i.e., 



h 



d 



DUST PARTICLE 

 _- CAUSING OPEN 

 CONTACT 



---^DUST PARTICLE 

 JUST CLEARED 



Fig. 3 — Particle in open zone. 



