[time-nuts] Tbolt temperature sensor
GandalfG8 at aol.com
GandalfG8 at aol.com
Thu Feb 5 10:14:55 UTC 2009
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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