[time-nuts] Thunderbolt DAC vs temperature

Mark Sims holrum at hotmail.com
Sun Mar 8 21:42:45 UTC 2009

In holdover mode,  my Thunderbolt seems to vary the DAC voltage around 100 uV for a 150 millidegree C change.  For slowly  varying temperature changes the DAC seems to lag the temperature by around 60 seconds.  More radical temperature changes (like a spritz of freeze spray) get to the DAC in less than 10 seconds.  

The Thunderbolt filters the temperature sensor readings in firmware.  The filter seems to exhibit a very fast attack and a slow decay.  A glitch in the temperature readings (like when the sensor is on the edge between two 0.5C basic resolution raw reading levels) shows up as an instantaneous spike in the temperature plot followed a slow decay back to the proper level.


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