[time-nuts] Tbolt temperature sensor
df6jb at ulrich-bangert.de
Thu Feb 5 12:23:53 UTC 2009
I have been thinking about the DS18B20 with programmable resolution.
> -----Ursprungliche Nachricht-----
> Von: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Bruce Griffiths
> Gesendet: Donnerstag, 5. Februar 2009 12:14
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Tbolt temperature sensor
> As in the difference between the DS620 (10, 11, 12, or 13 bit
> directly with no additional calculation) and the DS1620 (9
> bits + 3bits extension via the procedure in the datasheet)?
> The original post did state that the sensor was a DS1620.
> Mark also stated in a later post that he had replaced the
> chip a new DS1620 with no effect on the resolution of the
> reported temperature.
> Ulrich Bangert wrote:
> > Gents,
> > has anyone checked which DALLAS part is REALLY inside the box?
> > I put forward this question because DALLAS has parts in their
> > portfolio that sell as "genuine" 12-bit resolution ones and
> other ones
> > that sell as 9-bit resolution ones where additional 3 bits of
> > resolution can be used by some "tricks" The software for these two
> > types is NOT the same.
> > Best regards
> > Ulrich Bnagert
> >> -----Ursprungliche Nachricht-----
> >> Von: time-nuts-bounces at febo.com
> >> [mailto:time-nuts-bounces at febo.com] Im Auftrag von
> GandalfG8 at aol.com
> >> Gesendet: Donnerstag, 5. Februar 2009 11:15
> >> An: time-nuts at febo.com
> >> Betreff: Re: [time-nuts] Tbolt temperature sensor
> >> In a message dated 05/02/2009 06:25:52 GMT Standard Time,
> >> holrum at hotmail.com
> >> writes:
> >> Actually, what is apparently going on with the newer
> >> Thunderbolts is worse
> >> than that. The reported temperature seems to only end in
> >> 0.25C or 0.75C, so
> >> it has an effective 0.5C resolution. The basic DS1620
> >> resolution is 9
> >> bits, but the Tbolt firmware reduces that to 8 bits since
> >> the first step in the
> >> high res temp algorithm is to mask off the lower bit.
> >> Whatever is going on
> >> they are not getting the extra resolution that they think
> >> they are, and in
> >> fact they are reducing the basic resolution of the chip.
> >> The firmware does seem do do some filtering on those values
> >> since whenever
> >> the reading steps you can see some smoothing going on. A
> >> lot of times the
> >> temperature value oscillatates around the step point. The
> >> filter apparently
> >> does not have any hysteresis.
> >> The older Thunderbolts produced a nice smooth curve. The high res
> >> temperature reading (Bruce says is 12 bit/0.0625C) coupled
> >> with the firmware filtering
> >> gave temperature curves with microdegree scale resolution.
> >> The newer ones
> >> clunk around with effectively 0.5C resolution.
> >> --------------------------------
> >> But have you actually established this has anything
> >> whatsoever to do with
> >> the oscillator conditioning and, if not, what effects are you
> >> suggesting it has
> >> on the conditioned output?
> >> Isn't it likely that a temperature sensor adjacent to the
> >> RS232 connector is
> >> just going to monitor unit temperature for environmental
> >> purposes, perhaps,
> >> for example, to give the option for flagging up an
> >> overheating situation, in
> >> which case surely 0.5C resolution is more than adequate and
> >> the "clunkiness"
> >> isn't really an issue?
> >> I agree it's always nice to know what's happening, and why,
> >> but I suspect
> >> the performance of this sensor has no relevance to the
> >> oscillator performance
> >> itself.
> >> regards
> >> Nigel
> >> GM8PZR
> >> regards
> >> Nigel
> >> GM8PZR
> >> _______________________________________________
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