wet and dry contacts

Discussion in 'General Electronics Chat' started by bigdog, Jan 15, 2006.

  1. bigdog

    Thread Starter New Member

    Jan 15, 2006
    I would like to know the definition of wet and dry contacts and inputs.
  2. beenthere

    Retired Moderator

    Apr 20, 2004

    Considering contacts, dry ones are just that - two conductive metal peices that are mechanically brought into contact in order to carry current. Wet contacts are found in sealed enclosures. The weting agent is mercury. Wet contacts are not particularly affected by wear and pitting, although they carry arcs with the greatest of ease. You do not want to be in a room where a big mercury displacement contactor has overloaded and blown mercury vapor all over.

    I think the wet inputs are an old dodge to avoid slip rings, such as when taking torque measurements from a rotating shaft. You arrange concentric cups holding mercury, so that each signal terminates in its own insulated cup. The signals get picked off by wires trailing in the contact cups. Not too healthy, but electrically quiet.