[time-nuts] Tbolt temperature sensor

Ulrich Bangert df6jb at ulrich-bangert.de
Thu Feb 5 12:23:53 UTC 2009


Bruce,

I have been thinking about the DS18B20 with programmable resolution.

Best regards
Ulrich

> -----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
> 
> 
> Ulrich
> 
> 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.
> 
> Bruce
> 
> 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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