[Nhcoll-l] [External] easy way to calibrate temperature humidity sensors

[Robert Waller]

Dear Chris,
It is actually not "a simple phase rule problem" but rather a diffusion kinetics problem.
If you have observed "My vessels are at constant RH for years at a time. The HOBO's monitor that." then you must have a well-sealed system without perturbation though I am not sure why you would want to set up such a steady state system.
Respectfully,
Rob

From: Tacker, Christopher <christopher.tacker at naturalsciences.org>
Sent: Wednesday, October 13, 2021 11:47 AM
To: Robert Waller <rw at protectheritage.com>; Lennart Lennuk <Lennart.Lennuk at loodusmuuseum.ee>; nhcoll-l at mailman.yale.edu
Subject: Re: [Nhcoll-l] [External] easy way to calibrate temperature humidity sensors

Waller's assrrtion is not true. My vessels are at constant RH for years at a time. The HOBO's monitor that. That's reliable. That's the reason you use a large volume of liquid for a small space. It's also the reason you keep dumping in NaCl until it fills the bottom of the vessel. It's actually a simple phase rule problem.

If anyone is interested, I have a bunch of scientific papers that utilize this technique.

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From: Robert Waller <rw at protectheritage.com<mailto:rw at protectheritage.com>>
Sent: Wednesday, October 13, 2021 11:21:24 AM
To: Tacker, Christopher <christopher.tacker at naturalsciences.org<mailto:christopher.tacker at naturalsciences.org>>; Lennart Lennuk <Lennart.Lennuk at loodusmuuseum.ee<mailto:Lennart.Lennuk at loodusmuuseum.ee>>; nhcoll-l at mailman.yale.edu<mailto:nhcoll-l at mailman.yale.edu> <nhcoll-l at mailman.yale.edu<mailto:nhcoll-l at mailman.yale.edu>>
Subject: RE: [Nhcoll-l] [External] easy way to calibrate temperature humidity sensors

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Thanks for posting this helpful information Chris.

It appears in the picture that there is a large volume of liquid solution.

To achieve reliable RH control a slurry with some solid above the level of the solution is required. Otherwise there will be stratification of more dilute solution across the top of the solution leading to a substantially higher than nominal RH level.

Rob



From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu<mailto:nhcoll-l-bounces at mailman.yale.edu>> On Behalf Of Tacker, Christopher
Sent: Wednesday, October 13, 2021 9:22 AM
To: Lennart Lennuk <Lennart.Lennuk at loodusmuuseum.ee<mailto:Lennart.Lennuk at loodusmuuseum.ee>>; nhcoll-l at mailman.yale.edu<mailto:nhcoll-l at mailman.yale.edu>
Subject: Re: [Nhcoll-l] [External] easy way to calibrate temperature humidity sensors



The link online to the paper is https://nvlpubs.nist.gov/nistpubs/jres/81A/jresv81An1p89_A1b.pdf<https://urldefense.com/v3/__https:/nvlpubs.nist.gov/nistpubs/jres/81A/jresv81An1p89_A1b.pdf__;!!HYmSToo!OZhDEgKay44ghmCSeJppH58LLmoUCqukf76pNDOwMEh2lYUfecpJK6c6C1zKckqlG-j1dHlSrloNEQ$>

Humidity fixed points of binary saturated aqueous solutions<https://urldefense.com/v3/__https:/nvlpubs.nist.gov/nistpubs/jres/81A/jresv81An1p89_A1b.pdf__;!!HYmSToo!OZhDEgKay44ghmCSeJppH58LLmoUCqukf76pNDOwMEh2lYUfecpJK6c6C1zKckqlG-j1dHlSrloNEQ$>

JOURNAL OF RESEARCH of the National Bureau of Standards- A. Physics and Chemistry Vol. 81 A, No.1 , January-February 1977 Humidity Fixed Points of Binary Saturated Aqueous Solutions

nvlpubs.nist.gov

The paper is also attached.  I've included a picture of the setup I use for controlled humidity experiments. I use a HOBO sensor to monitor the humidity and temperature, inside the lid.



Regards,

Chris Tacker





Chris Tacker  (he, him, his)

Research Curator, Geology |  Ph.D., P.G.,
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From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu<mailto:nhcoll-l-bounces at mailman.yale.edu>> on behalf of Lennart Lennuk <Lennart.Lennuk at loodusmuuseum.ee<mailto:Lennart.Lennuk at loodusmuuseum.ee>>
Sent: Wednesday, October 13, 2021 3:47 AM
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Subject: [External] [Nhcoll-l] easy way to calibrate temperature humidity sensors



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Hi!



In our herbaarium we have one quite old and one new temperature humidity sensor.

The data is quite diferent though these sensors are placed in the same spot.



Do you know any good and cheap ways to calibrate those senors?



Best regards!

Lennart Lennuk

Head of collections

Estonian Museum of Natural History

+372 6603404, 56569916


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