[time-nuts] temperature sensor
albertson.chris at gmail.com
Mon Jul 21 19:05:18 EDT 2014
Steam is always 100C in open air at sea level BUT there are real
problems if you try to use it
Steem quickly condenses back to water. If you think you can see steam
you are mistaken. What you see is water aerosol that is condensed
when stem hits the colder air. Water in vapor form is invisible in
air. For the same reason clouds are water, not vapor. If you place
the sensor in steam it is hard to really know what you have. Is it a
mixture of vapor, re-condenced vapor and air. And then what about the
thermal conductivity? You really can't know. But with water it is
pretty easy to see that it is nearly 100% water. Experiment with tap
water v. RO water and I doubt you will find much difference as "hard"
water has only maybe 12ppm dissolved minerals.
Same with dissolved gasses O2 and N2 at room temperature are present
at the small fraction of a gram per liter but at 100C there is not
much gas in the water.
Remember the raise in boiling point is (from memory) about .5C per
mole per liter and how many moles "stuff" is in a liter of 100C tap
water? You can calculate the effect. But I'm thinking it's way below
the 0.001C level.
Air pressure or altitude above sea level will make a real difference.
I once tried to cook rice at 12,000 feet. It didn't work.
On Mon, Jul 21, 2014 at 1:11 PM, Brooke Clarke <brooke at pacific.net> wrote:
> The temperature of steam can be anything above boiling water.
> Super heating of steam was common railroad practice.
> Boiling pure water will get rid of any trapped gases quickly.
> In fact this is the recommended thing to do to tap water before using it for
> freshly cut roses.
> Of course you need to let the water cool before putting them into it.
> Removing the trapped oxygen makes them last longer.
> Have Fun,
> Brooke Clarke
> Alan Melia wrote:
>> er not boiling water....steam. Water's boiling point is affected by the
>> dissolved gasses and other contaminants.
>> ----- Original Message ----- From: "Bill Dailey" <docdailey at gmail.com>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at febo.com>
>> Sent: Monday, July 21, 2014 5:43 PM
>> Subject: Re: [time-nuts] temperature sensor
>>> Ice water and boiling water coupled with altitude will give you two
>>> Sent from mobile
>>>> On Jul 21, 2014, at 10:12 AM, Attila Kinali <attila at kinali.ch> wrote:
>>>> On Mon, 21 Jul 2014 04:39:51 -0700
>>>> Alexander Pummer <alexpcs at ieee.org> wrote:
>>>>> NTC are not that very stable, they are amorphous material winch could
>>>>> recrystallize slowly and therefore change it's electrical behavior ,
>>>>> PT100 style is more reliable since it is pure metal
>>>> How long is the time constant for NTCs?
>>>> I guess, it wouldn't matter for most of the measurements we do,
>>>> as NTCs need to be "calibrated" before precision measurements
>>>> anyways. Unless one measures over several months, or years.
>>>> But on this timescales, i wouldn't really trust an off the shelf
>>>> PT100 either. Not unless i measure its stability
>>>> For use in GPSDOs and OCXOs, i guess it doesn't really matter,
>>>> as long as the NTC stays within spec. There an external loop
>>>> corrects for the variation/drift of the measurement.
>>>> While we are at it: what is a good way to calibrate/characterize
>>>> temperature sensors that is available to hobbyists?
>>>> Attila Kinali
>>>> I pity people who can't find laughter or at least some bit of amusement
>>>> the little doings of the day. I believe I could find something
>>>> even in the saddest moment, if necessary. It has nothing to do with
>>>> superficial. It's a matter of joy in life.
>>>> -- Sophie Scholl
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