RELAYS AND RELATED MECHANISMS 



contact gaps are correct. The process of increasing the tension in a spring is 

 illustrated in Figure 34.7; the inverse process is used to decrease tension. 

 When adjusting break buffer springs, the armature should be operated 

 manually to lift the lever spring clear. 



The lever springs are next adjusted : make lever springs should bear on the 

 armature or on the contact set below so that a force of 6 g wt is needed to 

 lift them. Break lever springs should be tensioned until they lift the adjacent 

 buffer spring clear of the buffer block when the relay is unoperated. Both 

 tips of twin contacts must touch simultaneously, and cylindrical heavy-duty 

 contacts must meet squarely. Necessary adjustments can be made with the 

 two-pin tool. 



As a final test, the relay armature should be operated by hand and checked 

 for smoothness of movement. The contacts should be inspected at the same 

 time; in the unoperated condition all lower buffer springs should be clear 

 of the block, while in the operated position the upper buffer springs should 

 be lifted clear. All springs should be straight, and all contact clearances 

 adequate; furthermore, all break contacts should open before any make 

 contact closes. 



Operating power 



It is necessary when designing relay circuits to know what power is required 

 for a relay: (a) to operate; (b) not to operate; (c) to hold, once operated; 



^200 

 E 

 100 - 



50- 



20- 



§ 10 



Q_ 



2- 



Number of contacts 

 Figure 34.8 Power requirements of 3000 type relay 



and (d) to release. The power appropriate to each of these conditions 

 depends on the coil configuration, the number and type of contacts, the 

 thickness of the contact springs and the size of the residual gap. Estimating 

 the power in any particular case is a straightforward though laborious 

 process, for further details of which Atkinson^ should be consulted. Since, 

 however, for satisfactory operation of relays large factors of safety are 

 usually applied, it is possible to quote results which, while only correct to 



516 



