A Subminiature Polar Telegraph Relay

A new approach to the relay design problem has led to improved sensitivity, reliability, maintenance-free long life, and a considerable reduction of size and cost. Extremely efficient magnetic circuits having no ineffective reluctance and requiring no new contact materials permit a high degree of miniaturization of polar relays. To simplify the magnetic circuit, the permanent magnet is used both as the balanced armature and as the "permanent magnet" itself, with all of the air gaps in the magnetic circuit serving as effective reluctances to drive the armature. A characteristic equation obtained from an examination of the leakage flux and the internal reluctance of the permanent magnet is in good agreement with the experimental results. To improve the transmission performance, good chatter-free contact springs were used. Experimentally, it was determined that a stable contact resistance having a very long life is provided by the combination of a platinum contact and a gold-plated tungsten contact, hermetically sealed in inert gas containing a small amount of hydrogen. A subminiature polar relay recently developed for use in carrier telephony, telegraphy, and data transmission equipment has a volume of 2.9 cc, a weight of 10 gm, and an operating power of 0.5 mw. Transmission performance characteristics such as bias distortion and contact ratio are superior to any other widely used polar relays and are reliable enough to meet the environmental test of "MIL-R-5757D."