[time-nuts] Tbolt temperature sensor
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:
> 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
>> 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
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