[time-nuts] Tbolt temperature sensor

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Feb 5 11:14:24 UTC 2009


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
>> regards
>> Nigel
>> _______________________________________________

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