Evaluation of Contact Failure by Vaporized Organic Gases

The results of a study of contact-resistance increase due to vaporized organic gases generated in relays are reported. The study was intended to evaluate the kinds of vaporized organic gases that impair contacts and to investigate the mechanism of contact failure caused by contact activation. A desiccator simplified testing method was used to determine the influence on contact resistance of such factors as the saturated-vapor pressure and structure peculiar to each of the vaporized organic gases. It was found that the allowable concentration level of saturated-vapor pressure was about 1 x 10-2mm. Hg when the switching operation was conducted at 50-V dc, 100 mA and that polymerized substances containing a number of double bonds and substances including benzene rings remarkably increased the contact resistance. It was also revealed that contact resistance depended upon the amount and distribution of black powder produced on the contact surface, which varied with the type of organic gases generated. Accordingly, our new approach was to focus on contact failure attributable to the productive process of black powder, rather than on contact failure due to contact erosion as conventionally supposed in contact activation phenomena.