THE POST OFFICE 3000 TYPE RELAY 



A relay set up to within ±10 per cent of the figures given below may have a 

 life between adjustments of a million operations. 



Before attempting to adjust a relay, the coil retaining nut should be checked 

 for tightness. The armature travel should then be adjusted to 0-030 in. by 

 bending the armature suitably. A special tool is available for this purpose, 

 but a light hammer, delicately used, is an acceptable substitute. 



For contact adjustment two special tools are needed : (a) A spring balance 

 to measure the force at the contact tip; if a proper relay balance is not 

 available it is possible to use a piece of leaf spring suitably mounted with a 



Position of special spring adjuster 



Bending the spring and pressing upwards 



Stroking the spring 



d 



^ 



Bow in spring 



Final set in spring 



Figure 34.7 Tensioning a contact spring 

 (.By courtesy of J. Atkinson and Sir Isaac Pitman and Sons, Lid. from Telephony, 1948) 



scale which converts deflection into force at the tip. (b) A two-pin spring 

 stroking tool; while it is possible to adjust a relay with a pair of flat-nosed 

 pliers, the correct tool makes the process much more straightforward. The 

 buffer springs should be adjusted first: they should require a force of 20 g wt 

 to lift them clear of the buffer block. They should also be straight so that the 



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