Resistors for harsh environments resist sulphur degradation
Designed to operate in harsh environments where there are high levels of sulphur contamination, these products offer increased product lifespan compared to standard film resistors. In tests conducted by Bourns comparing its standard film resistors to its sulphur-resistant film resistors, the’ sulphur-resistant resistors provided 20 times greater operating lifespan over its standard device. This enhanced lifespan makes them particularly well suited for mission-critical applications such as industrial and automation equipment, power supplies and communication base stations.
High-sulphur environments include those where oils, lubricants or fossil fuels are present, polluted industrial areas that have high-sulphur contamination or generally where there are harsh, corrosive conditions. Normal factors such as temperature, humidity and air flow, coupled with the presence of sulphur-based gasses, contribute to the corrosion process and the formation of harmful silver sulphide, which ultimately can cause an open circuit condition and failure of the resistor. Adding to the problem is the design and materials used in typical thick film resistors, particularly the silver in the silver palladium internal terminal, which cause standard resistor components to be more susceptible to the ingress of sulphur-based gasses.
“In recent years, the long-term reliability of film chip resistors that must operate in high sulphur environments has become an important concern in multiple industrial and telecommunication market segments,” said Brian Ahearne, Product Line Manager at Bourns, Inc.
The tests Bourns performed used parts in a 2400 cm³ glass desiccator vessel where the vessel was heated to an elevated temperature of 105C to accelerate the effects of the sulphurization. The resistors were then measured at regular intervals to verify resistance and compare results.
The latest sulphur-resistant thick film resistor models are available in eight different footprints from 01005 up to 0603. They include CR0201-AS, CR0402-AS, CR0603-AS, CR01005-AS, CAY06-AS, CAY10-AS, CAY16-AS and CAT16-AS. They are manufactured using a thick film element printed onto a ceramic substrate and tested in accordance with the ASTM B809-95 method. Bourns also offers the new models with wide resistance, temperature coefficiency and tolerance options.
Bourns; www.bourns.com/products/resistive-products/sulphur-resistant
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