Humidity sensor

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Dear all
I want to know if you know a humidity sensro that can work to -80°C, I want to use it to calculate dew point.
any suggestions are welcome.

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I would expect at -80c that there would be little humidity due to any water vapour being frozen.

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Ali_dehbidi wrote:
sensro that can work to -80°C, I want to use it to calculate dew point.

http://en.wikipedia.org/wiki/Triple_point
Could you tell us at what pressures H2O is still in liquid phase at -80degC?

Preparing for a longer journey?

No RSTDISBL, no fun!

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Quote:
Could you tell us at what pressures H2O is still in liquid phase at -80degC?

There are some devices that they sell. See this
http://www.vaisala.com/en/products/dewpoint/Pages/DMT152.aspx

The problem is the price!
So do you happen to know something way cheaper, if I could sense humidity then there are lots of cheap ways to measure temperature and finally calculating dew point.

I love Digital
and you who involved in it!

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Brutte wrote:

http://en.wikipedia.org/wiki/Triple_point
Could you tell us at what pressures H2O is still in liquid phase at -80degC?

Even at well below the triple point, water still exerts a non-zero vapour pressure, which means that humidity will quite happily form at any pressure (1), including standard atmospheric pressure. For example, at the bizarrely named Troll Station, there is humidity:

http://www.wunderground.com/global/stations/89504.html

But back to the OP, UPSI in France claims to have capacitive sensors that work down to -90 C:

http://upsi.fr/products/sensor.html

Sorry, I don't know the price for their sensors.

- S

(1) Funny things happen at above the critical pressure, so YMMV there.

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That's an industrial scale sensor, even NIST traceable. I guess that makes it slightly more expensive than the sensor used in my $10 'weather' station...

You are probably looking for something like this.

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jayjay1974 wrote:
That's an industrial scale sensor, even NIST traceable. I guess that makes it slightly more expensive than the sensor used in my $10 'weather' station...

You are probably looking for something like this.


The sensor linked, specified with "Operating Temperature Range: 0°C to +60°C", is not even close to the OP's requirement.
Quote:
I want to know if you know a humidity sensro that can work to -80°C

For pricing, some of the UPSI sensors are available at Saelig and seem quite reasonable.

Stan

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Quote:
For pricing, some of the UPSI sensors are available at Saelig and seem quite reasonable.

Which model do you suggest? I have seen all of them, and none of them seems to work till -80°C,
Most of them work till -40°C ,And I think for -40 I can use SHT75..It’s way more cheaper and more accurate!

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I overlooked the -80 requirement. In what application does it get so cold?

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Quote:
overlooked the -80 requirement. In what application does it get so cold?

In military warheads! :D

In some food processing systems, In some air conditioners, etc...

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In military warheads! [smile]

Careful, Ali! You might easily be taken seriously. Fair or not, your country-of-origin will likely make a lot of people nervous.

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington]

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I had a good laugh, .... I like that kind of humor :)

Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips

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Quote:
Careful, Ali! You might easily be taken seriously. Fair or not, your country-of-origin will likely make a lot of people nervous.

lol...if you smile the world reflection would be a smile!
Like plons respnose.

I love Digital
and you who involved in it!

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Ali_dehbidi wrote:
Quote:
For pricing, some of the UPSI sensors are available at Saelig and seem quite reasonable.

Which model do you suggest? I have seen all of them, and none of them seems to work till -80°C,
Most of them work till -40°C ,And I think for -40 I can use SHT75..It’s way more cheaper and more accurate!

From the Saelig link navigate: Components/Sensors/Ambient

These three are specified: "Ambient temperature (AT) from -90°C to 85°C"
- UPSI G-US.12 Very Low Temperature Humidity Sensor US$6.77
- UPSI G-US.13 Plugable Low Temperature Sensor US$8.05
- UPSI G-TUS.13 Dual Channels Low Temperature Sensor US$8.38

Stan

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But what is your application?

I witnessed a few HALT tests where a product is mercilessly tortured with vibrations (random up to 80Grms) and temperature variations. To get low temperatures quickly (> 65C/min) it uses liquid nitrogen. I saw peak temperatures of -100degC.

Quite a cool machine ;)

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Quote:
From the Saelig link navigate: Components/Sensors/Ambient

These three are specified: "Ambient temperature (AT) from -90°C to 85°C"
- UPSI G-US.12 Very Low Temperature Humidity Sensor US$6.77
- UPSI G-US.13 Plugable Low Temperature Sensor US$8.05
- UPSI G-TUS.13 Dual Channels Low Temperature Sensor US$8.38

Stan


Thanks stan.

I love Digital
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JohanEkdahl wrote:
Quote:
In military warheads! [smile]

Careful, Ali! You might easily be taken seriously. Fair or not, your country-of-origin will likely make a lot of people nervous.

Somehow, I can't imagine a defence contractor asking for technical help on avrfreaks.

jayjay1974 wrote:
But what is your application?

Well, food processing was mentioned, and -80C is the sublimation temp for dry ice, so my guess would be ice cream:

http://www.itv.com/food/recipes/hestons-bacon-and-egg-ice-cream

Incidentally, for the OP, you mentioned this sensor:

http://www.vaisala.com/en/products/dewpoint/Pages/DMT152.aspx

Although it's speced for a dew point of -80C, its ambient temp rating only goes down to -40C. If your ambient requirements are only -40C, then there are many humidity sensors that work at that temp, including the sensiron SHTx and the measurement specialties sensors:

http://www.meas-spec.com/humidity-sensors/humidity-sensor-components.aspx

- S

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Quote:
Somehow, I can't imagine a defence contractor asking for technical help on avrfreaks.

Neither can I. Others might, and that was my point.

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington]