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Join Date: Jun 2020
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Absolute Humidity Measurements

06/22/2020 2:04 AM

What instruments can I use to measure absolute humidity in air?

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Guru

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#1

Re: Absolute humidity measurements

06/22/2020 2:12 AM

Sling psychrometer, thermometer, barometer and this calculator...

https://planetcalc.com/2167/

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Guru
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#2

Re: Absolute humidity measurements

06/22/2020 4:18 AM

This should help.

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Guru

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#3

Re: Absolute Humidity Measurements

06/22/2020 10:02 PM

Measurement Capabilities

Humidity measurement instruments and hygrometers can sense a number of different factors.

Absolute humidity, expressed as grams of water vapor per cubic meter volume of air, is a measure of the actual amount of water vapor or moisture in the air, regardless of the air's temperature.

Relative humidity (RH), expressed as a percent, also measures water vapor, but relative to the temperature of the air.

The dew point temperature, which provides a measure of the actual amount of water vapor in the air, is the temperature to which the air must be cooled in order for that air to be saturated and dew to form.

https://www.globalspec.com/learnmore/sensors_transducers_detectors/humidity_moisture_sensing/humidity_measurement

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Guru

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#4

Re: Absolute Humidity Measurements. Fermi Tradition

06/23/2020 12:47 AM

Measuring Absolute Humidity on an Electronic Scale with a Frosty Tin Cup

Equipment:

A 1 cubic meter volume cardboard box cube. A tin cup glued half way protruding through a cardboard ring which is slightly larger than a round hole in the top of the cardboard box. Enough liquid nitrogen to half fill the tin cup. An electronic scale set to measure in grams.

Procedure:

Let the air to be measured enter the cardboard box. Set the scale to accept a tare. Use the empty cup with the cardboard ring as the tare. Use the cup and cardboard ring to close the hole in the top of the box. Add the liquid nitrogen to the cup. Wait a consistent amount of time, say 5 minutes. Toss out the remaining liquid nitrogen leaving the inside of the cup empty but leaving the frost on the outside of the cup. Weigh the cardboard ring, the cup, and the frost before the frost has a chance to fall off or melt.

Read the original Absolute Humidity of the air in the box as the grams of frost clinging to the cup which should be the reading on the display if you followed the tare instructions.

____________

thewildotter

P.S. Calibration of this instrument, which is basically choosing the time for frost to accumulate, is left as an exercise for the reader. Not all the air inside the box will be totally desiccated but some frost may freeze on the surface of the cup near the ring from water vapor not originally from inside the box. There are no controls for ambient air pressure or temperature fluctuations. The box will suck in some extra outside air moisture because the temperature of the air inside the box is decreasing. YMMV This "instrument" is in the tradition of Fermi confetti dribbling to measure the yield of early nuclear blasts.

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Guru

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#5

Re: Absolute Humidity Measurements

06/23/2020 3:48 AM

This will do it:

http://www.h2oop.com/

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#6

Re: Absolute Humidity Measurements

06/24/2020 6:31 AM

A chart is a useful thing to have to hand.

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Guru

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#7
In reply to #6

Re: Absolute Humidity Measurements

06/24/2020 6:42 AM

That is correct,but it takes a little learning curve to read it properly,something most people do not take the time to do.

I still use a hand sling unit..with built in slide rule.

KISS!

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#9
In reply to #6

Re: Absolute Humidity Measurements

06/24/2020 7:25 AM

...plus two thermometers, a piece of cotton wool, an elastic band, and a little water. Here is one already manufactured into a commercially-available unit:

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#8

Re: Absolute Humidity Measurements

06/24/2020 7:23 AM
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Anonymous Poster (1); HiTekRedNek (2); PWSlack (2); Rixter (1); SolarEagle (1); The Prof (1); thewildotter (1)

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