[time-nuts] Tbolt temperature sensor

Ulrich Bangert df6jb at ulrich-bangert.de
Thu Feb 5 10:23:44 UTC 2009


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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