[time-nuts] Strange temperature peak

[Will Matney]

I am glad someone finally said this, as after I read a few explanations, I
could see that the temperature reading would be off somewhat, especially in
the resolution used.

Thanks,

Will

*********** REPLY SEPARATOR  ***********

On 5/28/2011 at 11:53 AM Tom Van Baak wrote:

>The problem is actually with all three parts: the 1620 sensor, TBolt
>firmware, and with Heather. Let me explain.
>
>1) While the root cause is an anomaly in the DS1620 chip, Dallas
>identified (not solved) it and described a work-around after Weather
>Station users noticed glitches in the late 90's.
>
>2) The next problem is Trimble did not implement the recommended
>software fix in their TBolt firmware. Worse yet, Trimble computes a
>running average temperature and returns this as "the temperature"
>instead of the actual instantaneous 1620 reading. Further they use
>24-bit floating point precision in the TSIP packet. Side effects:
>a) the returned temperature is biased and late due to the LPF,
>b) users can mistake filtered floating point for mK or uK resolution,
>c) any 1620 glitches are "smoothed" instead of handled as Dallas
>suggested, and d) internal disciplining algorithms may use the bad
>temperature values as input.
>
>3) The final issue is that LH displays the filtered TSIP temperature
>rather than the actual 1620 temperature reading. Thus you often
>see exponential curves in temperature plots instead of true steps.
>And glitches too.
>
>Anyway, since we can't change the 1620 design; and we can't
>change the TBolt firmware, the solution for Alberto (and anyone
>else) is for LH to report the correct temperature.
>
>Mark -- the trick is to recreate the raw quantized 1620 temperature
>from the TSIP averaged temperature readings and then implement
>the 1620 glitch fix per the Dallas memo. This way the readings are
>on-time, reflect the actual ~1/140th C quantization of the chip, and
>have no glitches. The difference is dramatic.
>
>To de-average see at unavg.c in www.leapsecond/tools/
>
>To de-glitch see the Dallas memo 2000-ds1820-report.pdf under
>www.leapsecond.com/pages/tbolt-1620/
>
>/tvb
>
>
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