[time-nuts] Aging rate of crystals

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Feb 18 05:24:54 EST 2008


The dielectric constant of air has a tempco of about 5ppm/C

The variation  of the dielectric constant of air with humidity is about 
+ 1.4ppm per %RH.
The dielectric constant of air has a pressure coefficient of about 
100ppm/atm.

The rapid variations in frequency may be due to variation of fringing 
capacitances and the capacitance of any air dielectric trimmer caps with 
humidity.
The time constants for the absorption and desorption of water by epoxies 
and other plastics may be so long that the effects of the variation of 
water content of circuit board and other plastics surrounding the 
oscillator components on oscillator frequency are masked by aging.

Bruce



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