Abstract

Synopsis

Electrical Resistance Box Contacts

  • (1) Taper plug contacts are unreliable for careful work as their resistance varies with the chance position, firmness of seating, condition of contact surfaces, and use of neighboring contacts.
  • (2) Mercury cup contacts have the mechanical disadvantage of the spread of mercury over the surfaces and through the metal, and the electrical disadvantage of variable resistance due to the difficulty of keeping the mercury path constant.
  • (3) Taper plug contacts when lubricated with oil have much more steady but materially higher resistance.
  • (4) But when made of copper and lubricated with mercury, the contact resistance is greatly decreased, to 17 of that of clean metal surfaces, and also becomes much more constant. The resistance of the contact is only slightly dependent on tightness of seating and on age; the contact surfaces do not cut, or squeeze out; they cement themselves together but may be separated without damage. Resistance may be trusted to 10−6 ohms.
  • (5) The design of sets of contacts should be such as to give great strength and independence between contacts. Several designs are illustrated.

© 1922 Optical Society of America

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References

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