BALANCED POLAR MERCURY CONTACT RELAY 



1397 



we obtain 



h = 0.0338 



\Ri Ri) 



cm. 



(3) 



Fig. 3 shows a cross section of the armature and pole-piece at the 

 contact, indicating the configuration of the mercury in the grooves and 

 around a closed contact, as determined from equation (3). In the grooves, 

 it will be noted, the surface is concave cylindrical, with a radius of 

 -0.0163 cm, providing a path from the reservoir at this height with 

 nearly the full capacity of the groove. The contact angles to the armatuie 



R2 = -0.0163 CM 

 |Rl = 00 



I R, = 0X)263CM 



DEPTH OF WEAR 



MERCURY 



(2.07 CM ABOVE 



RESERVOIR) 



Fig. 3 — Cross-section showing configuration of mercury surface in grooves 

 and around closed contact. 



and platinum alloy contact surfaces are all zero, as these show complete 

 wetting. The mercury fillet around the contact has positive curvature 

 in the plane of the armature {ft\ = +0.0178 cm) and negative curvature 

 (i?2 = —0.0085 cm) in planes through the axis of the contact. 



The depth of wear indicated in Fig. 3 is brought to a stable value by 

 an aging process in production. 



DYNAMIC MERCURY CONFIGURATION 



Fig. 4 shows flash photographs of the contacts at various instants 

 during operation at 60 cps. It will be noted that, as the armature moves 

 away from the fixed contact on the right, Figs. 4(a), (b) and (c), a bridge 

 is drawn out which breaks in two places, leaving a free drop which falls 

 out, Fig. 4(c). 



