[time-nuts] Thermal Time Constant

Brooke Clarke brooke at pacific.net
Tue Mar 9 23:52:57 UTC 2010


Hi:

For some time I've considered surrounding a free running 32678 Hz 
oscillator (like a Dallas 32khz, or one of the newer Maxim units) with 
thermal mass and insulation in order to get the time constant into the 
range of some days.  To get a feel for it a simple experiment shows that 
a half inch diameter brass rod 3.75" long (102 grams) has a thermal time 
constant of about 6 min 35 seconds when wrapped lightly in a towel.

Is there a way to calculate the amount of aluminum and Styrofoam needed 
to get a time constant of say 100 hours?

This came up in relation to WWVB clocks that free run for most of the 
time.  When you compare WWVB clocks it's not uncommon to see tens of 
seconds difference between them.  http://www.prc68.com/I/Loop.shtml#TC

-- 
Have Fun,

Brooke Clarke
http://www.PRC68.com






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