Influence of the contact material on the performance oftemperature-dependent switching controllers in household appliance

摘要

Due to their design, the switching behavior oftemperature-dependent electro-mechanical switching controllers iscompletely different to electromagnetically driven devices, especiallywith regard to opening operation. Usually the expansion of a medium(e.g. liquid, bimetallic strip) is used to initiate the switchingoperation and thus the break operation is slow. As a result, sticking orwelding of contacts can occur, leading to troublesome exceededtemperature or reduced service life. Electrical tests with variouscontact materials were carried out in a model switch designed to meetthe switching conditions in switching controllers. It could be shownthat silver/tin oxide containing merely 2% by weight of metal oxide (tinoxide+additives) has significant lower opening forces. Tests in a realpower controller could be clearly improved by the application of thisspecial silver/tin oxide contact material. The way this doped tin oxideworks is tried to be explained by means of metallographic investigation