MALVERN, Pa., 5 June 2009. Vishay Intertechnology Inc. in Malvern, Pa., is introducing mil spec bulk metal foil Accutrim trimming potentiometers designed to meet the military standard requirements of MIL-PRF-22097 Char. F.
These parts, which are for avionics, military, and space applications, are on the military Qualified Parts List (QPL), administered by the Defense Supply Center Columbus (DSCC).
The QPL-approved 1/4 square-inch RJ26-style devices offer low end-to-end TCR of plus-or-minus 10 ppm/ degrees Celsius from – 55 degrees Celsius to + 150 degrees Celsius, + 25 degrees Celsius ref., and plus-or-minus 25 ppm/ degrees Celsius through the wiper, load life stability of 0.1 percent typical under full rated power at + 85 degrees Celsius for 1,000 hours, and a < 0.05 percent typical settability.
Vishay's 1242 series of trimmers has a bulk metal foil resistive element with temperature and load life stability. Vishay foil trimmers have a multi-fingered wiper traversing a flat element. The wiper engagement pressure can be much higher when the load is spread out over various wiper tangs, so the sensitivity to shock and vibration in foil-based trimmers is eliminated for most applications. Cermet trimmers have a much greater mass of the rider block and begin to show response to the lower frequencies of vibration and shock.
For high-reliability AMS applications, the 1242 devices are required when the value of resistance or voltage division in a circuit must be adjusted to compensate for environmental influences, when the desired circuit performance cannot be procured and retained through manufacturing, or it is unknown what precision is required.
The devices offer a multi-fingered, noble metal wiper engaging a planar surface of etched foil for low TCR end-to-end (five times tighter than required by MIL-PRF-39035 Char. H) and through the wiper. Other technologies, such as wirewound and cermet trimmers, have a much higher TCR end-to-end, and cannot be relied on to demonstrate an acceptable TCR through the wiper, which is an important element in the precise adjustment of circuits subject to temperature fluctuations.
For more information contact Vishay online at www.vishay.com.
