Re: [time-nuts] temperature sensor
Hi
If you want to hit 1 mK with your home made triple point cell, you will need a source of very clean water and some luck with materials and cleaning processes. If you want to go below that level, you will need an isotope readout on your water source. Rain water, and mid-continent well water are a bit different in their composition …. If I remember correctly, you want the mid-continent deep well stuff, but only from the “right” sort of well.
Yes I’d bet there is a water isotope nuts mailing list somewhere ….
Bob
On Jul 21, 2014, at 8:10 PM, Attila Kinali attila@kinali.ch wrote:
To satisfy my curiosity and get actual data I'd like to place 6 or more
tiny analog high-resolution temperature sensors all around the OCXO of a
Trimble Thunderbolt. That's high-resolution both in temperature and in time.
In other words, no fake accuracy "averaging" allowed. The goal is to observe
thermal gradients in real-time and see how good, or how bad, the correlation
is among crystal temperature, case temperature, and DS1620 temperature
sensor (which is mounted a considerable distance from the OCXO). The same
technique, and maybe even the same conclusions, might apply to Rb.
Ok... a couple hours of reading later.... ;-)
My excursion into temperature measurement has brought some results:
-
PT sensors can be secondary standards for temperature calibration.
But standard industrial sensors do not have the stability or linearity
of the standard grade sensors. But at least they do not break when you
glare at them. Those in ceramic housing are supperior to those in glass
or metal housing. Thin film are inferior to wire wound. (in terms of
stability and accuracy, thermal coupling is a different matter)
(the price for a commercial standard grade PT sensor seems to be in
the order of 3kusd) -
The uncertainty of the calibration of the standards grade PTR seems
to be in the order of 100uK to 10uK. -
Making a triple point of water cell for calibration with an accuracy
better than 10mK seems to be quite simple and doable at home, most
likely something around 1mK is achievable. Also judging the quality
of the cell is quite simple: make multiple of them, the one with the
highest temperature is the most accurate one. -
A well done ice bath gets you into the ballpark of 10mK accuracy.
Most of the error is due to impurities and gas in the water.
The air pressure effect is much smaller (and thus inconsequential)
unless living on a high mountain. Also an ice bath is easier to
do than using an triple point cell. -
There are people on ebay who sell very pure Gallium and Indium that
could be used for (not so accurate) melting/freezing cells for
~29.7°C and 156°C.
(if anyone knows what the non-nut would use those for, please tell me) -
The book "Traceable Temperatures" by Nicholas and White is a very good
reading on temperature measurement and calibration. It explains the
procedures with what can go wrong and what accuracies are achievable.
It also contains a list of references for further reading. I did not
have a look at those yet, but from the titles they look very reasonable.Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
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That is a great idea. Thank you.
I can see use for this on more then one project. I have some really
poor preforming traction motors on a small robot. This is one of
those flap your forehead "why did I not think of something so simple?"
events. I'll call it a "kick starter"
BTW, one project, years ago needed stable temperer. They placed the
part in a vacuum. If you really do need to decouple from the ambient
a vacuum gap will do it.
... I and has a "stall
routine" that gives the fan a kick if it stalls (NB: this is a feature of
the 642B, absent on the 642). So, not only will it run the fan at its
lowest possible self-sustaining speed, you can also run the fan much slower
than its self-sustaining speed by letting it stall and be restarted
periodically.
--
Chris Albertson
Redondo Beach, California
Absolutely nothing limits the temperature of steam in
air. It can easily be superheated to thousands of degrees F.
However, at the water/steam interface, the steam will be
exactly 100C at standard pressure as it vaporizes. Even if the
water is full of dissolved matter, and has a slightly higher
boiling point.
When I calibrate thermometers, I always use well stirred ice
water, and well stirred boiling water. I can't see getting
enough dissolved matter in distilled water to make enough of
a difference in the boiling point to matter to me.
-Chuck Harris
Attila Kinali wrote:
On Mon, 21 Jul 2014 18:00:59 -0400
Chuck Harris cfharris@erols.com wrote:
Steam superheats only if the pressure is raised above standard pressure,
otherwise, steam at standard pressure will be exactly 212F, or 100C.
Uhm.. you are the second one claiming this. Could you please explain
what physics limits the temperature of vapor?
The ideal gas equation says that p*V/T = const, ie that the temperature
can rise at a constant pressure, as long as the gas is allowed to expand.
Attila Kinali
The maximum temperature of saturated steam temperature depends on
pressure; unsaturated steam does not. At work, we just finished a
project using steam at over 800F to drive a jet mill.
Brent
http://en.wikipedia.org/wiki/Superheated_steam
On 7/21/2014 5:39 PM, Attila Kinali wrote:
On Mon, 21 Jul 2014 18:00:59 -0400
Chuck Harris cfharris@erols.com wrote:
Steam superheats only if the pressure is raised above standard pressure,
otherwise, steam at standard pressure will be exactly 212F, or 100C.
Uhm.. you are the second one claiming this. Could you please explain
what physics limits the temperature of vapor?
The ideal gas equation says that p*V/T = const, ie that the temperature
can rise at a constant pressure, as long as the gas is allowed to expand.
Attila Kinali
On Tue, 22 Jul 2014 01:17:03 +0100
Brian D groups@planet3.freeuk.co.uk wrote:
Saturated steam at standard pressure will be exactly 212F, or 100C.
Stupid question: How to you ensure that the steam is saturated,
while keeping a constant pressure?
I think just buying some indium off ebay and use that as a melting/freezing
reference is easier than the contraption needed to ensure fully saturated
steam, with a low temperature gradient over the temperature sensor.
That said. My investigations into stability of PT100 sensors reveal,
that the quality ones can be less than 10mK/year, but hysteresis is
in the same ball park (see [1]).
Attila Kinali
[1] "Long term stability and hysteresis effects in Pt100 sensors
used in industry", by Ljungblad, Holmstein, Josefson, Klevedal, 2013
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
Group,
I worked for Rosemount, a manufacturer of precision resistance
thermometers, for many years.
Platinum does have a well-known formula for temperature versus
resistance, with second order corrections.
But a sensor is not enough. You need to convert its physical property to
a signal that is useful.
This is done by some sort of temperature transmitter or conversion
device. The device and the RTD are a system.
The temperature system is calibrated as you would any other such system,
by comparing it to a standard that is 10 times more accurate.
So the question is, how accurate do you want it to be, just as it is for
time and frequency standards.
Boiling water with an ambient pressure correction is fine for some
systems. More accuracy requires more purified water and a better
pressure measurement. Similarly, the triple point of ice, water, and
vapor depends on purity and knowledge of ambient conditions, as well as
the heating effect of the stirrer. And that only gives you two points,
with no knowledge of nonlinearity in between or outside them.
There is plenty of literature on the subject, but it is not in the scope
of precision time and frequency measurement.
It is, however, summertime.
Bill Hawkins
In a container, as steam condenses the pressure will drop. The steam will stay saturated. This is as long as the container contains steam only. Eventually, as the steam cools and condenses you will be left with a vacuum contains only minimal water vapor.
Sent from mobile
On Jul 22, 2014, at 2:11 PM, Attila Kinali attila@kinali.ch wrote:
On Tue, 22 Jul 2014 01:17:03 +0100
Brian D groups@planet3.freeuk.co.uk wrote:
Saturated steam at standard pressure will be exactly 212F, or 100C.
Stupid question: How to you ensure that the steam is saturated,
while keeping a constant pressure?
I think just buying some indium off ebay and use that as a melting/freezing
reference is easier than the contraption needed to ensure fully saturated
steam, with a low temperature gradient over the temperature sensor.
That said. My investigations into stability of PT100 sensors reveal,
that the quality ones can be less than 10mK/year, but hysteresis is
in the same ball park (see [1]).
Attila Kinali
[1] "Long term stability and hysteresis effects in Pt100 sensors
used in industry", by Ljungblad, Holmstein, Josefson, Klevedal, 2013
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Tue, 22 Jul 2014 15:59:38 -0500
"Bill Hawkins" bill@iaxs.net wrote:
There is plenty of literature on the subject, but it is not in the scope
of precision time and frequency measurement.
I would like to disagree here. Precise time and frequency measurement
highly depends on precise control of temperature. Most of our devices
and tools have a rather high temperature dependence (high for time-nuts
needs ;-). Thus, i would like to ask you to share any good literature
you have. I've been reading up on this topic the last two days, but
merely scratched on the surface. Any pointer on good things to read
would be highly appreciated.
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
To ensure that steam is in a suitable state for temperature measurement
one uses a Hypsometer.
I made one out of tin cans and it sits on an electric hot plate.
It is not rocket science but it really works, my PT100 showed stable temperatures within a
milliKelvin.
It is made so that the splash is separated from the boiling water and the shielding surfaces
are maintained at the wet steam temperature. All that is necessary in the design is
that the pressure drop of the steam is kept below some reasonable number.
The catch is that you must measure the ambient pressure to great precision,
aneroid barometers are hardly good enough except for some specially calibrated devices,
solid state barometric sensors are orders of magnitude too insensitive,
and a mercury barometer (Fortin pattern) requires several calculated corrections
including the exact value of gravity at the measurement site.
cheers, Neville Michie
On 23/07/2014, at 5:11 AM, Attila Kinali wrote:
On Tue, 22 Jul 2014 01:17:03 +0100
Brian D groups@planet3.freeuk.co.uk wrote:
Saturated steam at standard pressure will be exactly 212F, or 100C.
Stupid question: How to you ensure that the steam is saturated,
while keeping a constant pressure?
I think just buying some indium off ebay and use that as a melting/freezing
reference is easier than the contraption needed to ensure fully saturated
steam, with a low temperature gradient over the temperature sensor.
That said. My investigations into stability of PT100 sensors reveal,
that the quality ones can be less than 10mK/year, but hysteresis is
in the same ball park (see [1]).
Attila Kinali
[1] "Long term stability and hysteresis effects in Pt100 sensors
used in industry", by Ljungblad, Holmstein, Josefson, Klevedal, 2013
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.