Elecromagnetic Relay Reliability Predictions by Designed Life Experiments and Weibull Analysis

The complexity of their failure mechanisms, the significant interaction effects of numerous operating parameters, and high test costs have led to many elaborate, expensive, time consuming, and often ineffective, test programs to characterize the life expectancy of specific relay designs under a variety of application conditions. This paper describes a program wherein a series of life tests of a newly developed relay, conducted in accordance with a factorial experimental design, graphical Weibull analysis, and appropriate computational techniques were combined to derive the functional relationship between its life expectancy and the operating parameters of load current, ambient temperature, and operating frequency over a broad range of stress levels. The results of the program are presented in the form of application data for use by the design engineer in assessing the expected life expectancy, or reliability of the design over a wide range of the parameters explored and the effect of "trading-off" operating parameters on the reliability of the device.