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Author: STEINKE, M
Abstract: Solid-state controls are now routinely employed to control safety-related functions in household electric ranges, ovens, and counter-mounted cooktops. Solid-state controls are generally more sensitive to physical and electrical environmental conditions than their electro-mechanical counterparts, and traditional test methods are inadequate to properly evaluate the reliability of solid-state devices. The Standard for Safety-Related Solid-State Controls for Household Electric Ranges (UL 858A) was developed to address the unique properties of solid-state controls and covers oven temperature regulating, temperature limiting, self-cleaning (pyrolytic) oven door lock, and cooktop element control applications. UL 858A is concerned only with a control's safety or protection functions. This paper presents an overview of the requirements in UL 858A, with an emphasis on applications. A "typical" solid-state control is followed through several phases of its safety evaluation using UL 858A and its companion Standards UL 244A and UL 873. The failure mode and effect analysis (FMEA) portion of the investigation is discussed in detail, touching on each of the concerns that form the basis of the reliability investigation. The demonstrated test method (DTM) and environmental stress tests are also discussed. This paper also includes an overview of the new requirements in the Standard for Household Electric Ranges (UL 858), which are applied to complete appliances employing solid-state controls, including mechanical endurance tests on membrane switch keyboard assemblies, environmental stress tests on the complete appliance, and shorted-thermostat abnormal operation tests.
Source: IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS
Publication Year: 1992
Volume: 28
Issue nr: 1
Pages: 239 - 250
Science Code: Engineering, Multidisciplinary; Engineering, Electrical & Electronic
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