Balanced Polar Mercury Contact Relay 



By J. T. L. BROWN and C. E. POLLARD 



(Manuscript received June 19, 1953) 



A new type of relay making use of solid contacts maintained continuously 

 wet with mercury has been developed. It has a symmetrical polar structure, 

 resulting in improved sensitivity and speed compared with the existing neu- 

 tral structure with similar contacts. It is also particularly well adapted to 

 switching of high frequency circuits. Two magnets are used for polarization, 

 and the relay is adjusted after assembly to desired values of sensitivity for 

 operation in both forward and reverse directions by selective adjustment of 

 the magnet strengths. 



INTRODUCTION 



In a previous paper^ a mercury contact relay is described in which the 

 contact elements are maintained wet with mercury through a capillary 

 path to mercury reservoir below the contacts. The present paper de- 

 scribes a new design making use of this same mercury contact principle, 

 but with a S3mametrical polar structure which gives improvement in 

 sensitivity and speed capabilities over the previous neutral structure. 



VERTICAL RELAY 



Fig. 1 shows one design of the relay, adapted for general use in a 

 vertical position. It provides a single pole double throw magnetic switch 

 in a sealed glass tube, enclosed along vnth an operating coil and polariz- 

 ing magnets in a steel can with a medium octal plug base similar to the 

 previous type relay (275 type). 



Fig. 2 shows the glass enclosed magnetic switch element. The armature 

 is a tapered reed welded to a tubular stem which is sealed in the glass at 

 the lower end. Mercury, and gas under pressure are introduced through 

 this tube, which is then welded closed. The magnetic working gaps are 

 formed between the armature and fixed pole-pieces which are sealed in 



1 J T L. Brown and C. E. Pollard, Mercury Contact Relays, Eloc. Enj?., 66, 

 Nov., 1947. 



1393 



