An experimental apparatus to simulate for air pollution on electrical contacts

Ammonium sulfate was found on the failed contacts for the speech path of the XS-type cross-bar switch in electronic switching systems at an earlier time. It was explained that the ammonium sulfate was formed by SO2 gas in the polluted atmosphere and NH3 gas emitted from the electromagnetic relays in the system. Simulation experiments free of harmful gases are described in this paper. It is noticed that an ultrasonic humidifier can generate not only pure water mist but also solution mist. If the solution involved ammonium sulfate, mist containing ammonium sulfate would be generated. After introducing the ammonium sulfate mist into dry air, fine particles of solid state ammonium sulfate may be deposited. Several kinds of materials were exposed to the atmosphere containing ammonium sulfate using experimental equipment to simulate air pollution on the electrical contacts. The kinds of exposed materials are noble contact metals such as Au, Ag, Pd, Pt, PGS and other alloys, and a few base metals such as Al, Phosphor Bronze, and Stainless Steel.