[time-nuts] Tbolt temperature sensor

Mark Sims holrum at hotmail.com
Wed Feb 4 05:45:55 UTC 2009

Well,  I replaced the DS1620 temperature sensor in my 2005 vintage Thunderbolt that shows the (mostly) flat temperature curve that is quantized to 0.25/0.75C increments (earlier models produce a smooth temperature curve that tracks minute temperature changes).  

The new DS1620 chip shows the same behavior as the old one.  Conclusion is that either Trimble changed the firmware (but did not change the  reported firmware revision number/date) or Dallas Semiconductor changed the DS1620 high resolution read mode in a way that messes up the Tbolt firmware (the DS1620 that I used did have a similar date code to the one I changed out). 

My bet is Dallas Semi changed their chip in a way that is not compatible with the Tbolt firmware.  If Trimble changed their firmware to not do the high resolution read cycle,  they would not have done the first steps of the high res read cycle (mask off the LSB,  subtract 0.25C)  which actually reduces the temperature resolution from nine bits to eight bits.

Trimble could have easily missed the problem if they did not plot the temperature curves.  The unit reports a proper temperature,  it just does not have the fine resolution of the earlier units...  which could easily affect holdover performance.

Does anybody out there have a late model (like 2005 date code) Tbolt (like from the second batch of TAPR units) that shows the smoothly changing temperature curves?  The pictures that Asa posted show the flat temperature curve.  All my 2002-2003 vintage units show the smoothly changing curve.  Lady Heather shows the date of manufacture on the third line down.
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