[time-nuts] FE-5680A temp coefficient seems to be -7E-12 per degree C

John Beale beale at bealecorner.com
Wed Dec 21 13:55:44 EST 2011


My measurements on one FE-5680A Rb sample indicate a temperature 
coefficient of -7E-12 per degree C (T measured at exterior case top 
center); more details below. Can anyone opine if this is a reasonable value?

I can't say anything about long-term drift until I stabilize the case 
temperature. Currently experimenting with a variable-speed fan and PID 
controller looking at a thermistor attached to the case, to that end.

The starting point of -3.2E-10 offset is just how the unit arrived, I have 
not yet tried changing the frequency via RS-232 commands.

With a 40mm 12V fan running at 5V and pointed at a 4x6x1" finned heatsink 
the unit is mounted on, the case temp. drops 10 degrees (55C -> 45C), and 
the unit 15Vdc power draw increases 2 watts. (Perhaps a bit less, I 
actually measured the power at 120Vac with a WattsUp Pro meter, but I 
assume my DVE 15V 2A switcher is pretty efficient. Supply is from 
lightobject.com and actually provides 14.84 V, but that seems to work.) 
Ambient room temp was also logged; it varies by about 2 C as building 
heater cycles.

FE-5680A 10 MHz F_offset vs. GPS using picPET:
http://www.leapsecond.com/pic/picpet.htm
and Sure Electronics GPS:  http://www.leapsecond.com/pages/MG1613S/
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Foff = -3.20E-10  7:30 am Dec.14 2011 (32 hours). Case top: ~45 C
Foff = -3.22E-10  9 pm Dec. 15 2011 (14.5 hours). Case top: 41.5-44.5 C
Foff = -3.227E-10 3 pm Dec. 17 (40.9 hours). Case top: 42-44 C	
Foff = -3.216E-10 11 pm Dec. 19 (46.5 hours). Case top: 42-44 C	
Foff = -3.902E-10 10 am Dec 20 (11 hours). Case top: 52.5-53.5 C (fan off)
Foff = -3.910E-10 10 am Dec. 21 (12 hours of data). Case top: 52.5-53.5 C

conclusion: tempco is -7E-11 with +10 C, or about -7E-12 per degree C
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see also: https://picasaweb.google.com/109928236040342205185/FE5680A
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