[time-nuts] temperature sensor
jwsmail at jwsss.com
Mon Jul 21 16:51:35 EDT 2014
On 7/21/2014 11:36 AM, Hal Murray wrote:
> docdailey at gmail.com said:
>> >Ice water and boiling water coupled with altitude will give you two points.
> Has anybody used a good thermometer to measure air pressure?
> How much does the measured temperature vary between just barely boiling and a
> good roiling boil? Or in various locations within a pot of boiling water?
When you are dealing with water phase changes, you are dealing with both
temperature and heat. When you get up to a point like boiling, you have
a mass of water which is at the local boiling point and the only thing
stopping the water from going to steam phase is the amount of heat in
the water. Once a pot of water is at rolling boil all of the water in
the pan should be at and stay at the boiling point till it is all gone.
Once you remove the heat, the boiling will slow and stop, and the
temperature will begin to fall as the water loses the heat.
As long as you maintain a balance between having the sensor too close to
the point you are applying heat, and keeping it immersed in boiling
water, you should be able to assume the local boiling point. That
boiling point has to be adjusted for pressure, which affects the temp
the most. Also assuming only water, and no other contaminants as
mentioned by another poster.
The same sort of action occurs when water freezes, along with some other
oddball issues with the crystalization. You can arrive at the freezing
point, and you will dwell there for some time as the water loses its
heat and becomes solid.
The thing that is different between freezing and boiling is that as long
as you have water and are boiling the temperature will remain at
boiling, and no higher.
With freezing, if you are measuring water as you cool it and remove
heat, it will go thru freezing with a pause as it goes to ice, then it
can continue to cool as cold as you like.
so when you are measuring by using ice as a reference, you should have
frozen the sensor or drilled it into the center of a block of ice, and
let it come to equilibrium in the ice w/o any freezing apparatus being
active. It should come to the freezing point till all of the ice melts.
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