Changes

Electrical life, failure rate and reliability are statistical quantities. To determine the electrical life, the relays are switching the specified load in an accelerated way with higher switching frequency, until the first pre-defined failure occurs. The number of switching operations reached for the representative sample size of relays is determined through statistically valid test setups using Weibull distributions. For all switching operations, the failure criteria must be monitored and recorded.

<figure id="fig:Statistical evaluation of the electrical life of relays">

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The DC load conditions are specified in the relevant standards (for ex. Telecom Specifications).

<figure id="fig:Principle and sequence of testing with electronic load simulation">

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<figure id="fig:Automotive relays under motor load">

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The full clarification of causes for switching device failures, for example relays, is most important for quality assurance. As a starting point, the full history of the relay, such as electrical load, environmental conditions etc. must be recorded. The process flow chart in (<xr id="fig:Flow diagram for evaluation of failure cause in switching devices for communications technology"/><!--(Fig. 13.10)-->) clearly describes a proven way to conduct a failure analysis.

<figure id="fig:Flow diagram for evaluation of failure cause in switching devices for communications technology">

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Following all procedures of such a failure evaluation carefully, the root cause of the defect can most likely be established in order to implement preventive measures limiting future occurrences.