RELAYS AND RELATED MECHANISMS 



for a d.c. voltage of at least 50 V to be applied to the contacts through a 

 high resistance (^^50 kQ) in addition to the small signal voltage. 



Projecting from the side of each non-moving (or 'buffer') spring is a small 

 tag which engages v>/ith a step on the buffer block. This serves two purposes : 

 (a) by pre-tensioning the buffer spring on to the buffer block it is possible 





TT 



Make 



(M) 



s: 



Break 



(B) 



:^ 



Change - over 



(C) 





s: 



TF 



Make - before - break (K) 



Figure 34.5 Types of relay contact 



\M. 



^ 



Figure 34.6 Spring with twin contacts 



to ensure adequate contact pressure ; (b) if the spring is kept straight the 

 position of the buffer block steps determine the contact clearance. It is 

 largely from the buffer block that a relay achieves reliability; operation 

 with unsupported springs can only lead to trouble. 



Buffer blocks are available with 1 , 2, 3 and 4 steps on each side, and with 

 3 steps on one side and 4 on the other. All available contact assemblies can 

 thereby be buffered. 



Adjustment 



For reliable operation a relay must be properly adjusted. For certain 

 applications it may be necessary to use light spring tensions and short 

 armature movements; it must, however, be understood that reduced power 

 handling capacity of the contacts and greater probability of failure due to 

 dust will be the inevitable results of unorthodox adjustments of this type. 



514 



