Lost in Space: Unpredictable Aging Can Send Resistor Accuracy Way Off Course
by Steve Sandler and Charles Hymowitz, AEi Systems, Los Angeles, Calif., How2Power Today, May 27 2010
Focus:
M55342 chip resistors specify tolerances as tight as 1% with aging on the order of 0.2% after
10,000 hours. Unfortunately, such specifications do not predict how resistors will age when
subjected to the extreme temperatures encountered in space. So what is an appropriate aging
tolerance for film resistors? To answer this question, designers may turn to the many
specification and guideline documents that offer aging tolerances for resistors in space
applications. Unfortunately, these specifications are often ambiguous, arbitrary or even
contradictory. In this article, an attempt is made to analyze the aging tolerance of M55342
thick-film chip resistors from different perspectives, assess the validity of the different
guidelines on resistor aging, dispel common myths, and suggest possible solutions for dealing
with the unpredictability of resistor aging. The authors present a modified Arrhenius equation
and show how it can be used to calculate resistor aging (expressed as a resistor tolerance) at
different temperatures, using actual resistor aging data to curve fit the data to the equation.
They demonstrate the sensitivity of the equation at high temperatures to the value of
activatation energy, and why a lack of industry consensus over the appropriate value of
activation energy for film resistors is problematic.
What you’ll learn:
- How to predict the aging tolerance of thick-film resistors in space applications
- How to predict the tolerance of thick-film resistors as a function of time and temperature
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