salt test - how long?

[earthson]

Nope - and this with regard to all what youre stating - sorry.

Yeah, I guess all I have is Chemistry and Physics backing me up - sorry.

[Smallclub]

As someone as stated above, calibrate as close to your desired humidity as possible. When calibrating with the salt test method, you aim for 75 rh.

please define "calibrate"…

You don't "aim" for anything with the salt test, you simply try to know the delta between reliable data (75% provided by the salt+water mixture) and the measurement given by a hygrometer, and you adjust if the device permits to do so.

The process is exactly the same if the reliable data is given by a 60% Boveda set.

[TomF]

Yeah, I guess all I have is Chemistry and Physics backing me up - sorry.

Don't Bovedas use a salt solution? Why would calibrating with Boveda be any different with regard to NaCl coming into contact with water?

[Fugu]

Yeah, I guess all I have is Chemistry and Physics backing me up - sorry.

Guess that must be the Comedy-part?…

But if you believe so – fine. Saves my time of explaining it.

No offence meant, RoRo, but the only correct statement in your posts so far has been:

[Fugu]

Don't Bovedas use a salt solution? Why would calibrating with Boveda be any different with regard to NaCl coming into contact with water?

Correct of course! Same underlying principle. The only thing Boveda/Humidipack did, was getting it into a handy packaging.

[CBMC]

please define "calibrate"…

You don't "aim" for anything with the salt test, you simply try to know the delta between reliable data (75% provided by the salt+water mixture) and the measurement given by a hygrometer, and you adjust if the device permits to do so.

The process is exactly the same if the reliable data is given by a 60% Boveda set.

I think, and now I am speaking for someone else, what the poster meant was to use hygrometer calibration as close to the humidity that you store your cigars at. I have seen hygrometers that read 75% with a 75% boveda and 56% with a 62% boveda. This being the same hygrometer. So the offset wasn't exactly linear across the humidity range. So either make a mental note of the difference or, if the hygrometer is adjustable, adjust while using a boveda pack closer to the humidity the cigars are stored.

Sent from my Nexus 6 using Tapatalk

[Fugu]

I think, and now I am speaking for someone else, what the poster meant was to use hygrometer calibration as close to the humidity that you store your cigars at. I have seen hygrometers that read 75% with a 75% boveda and 56% with a 62% boveda. This being the same hygrometer. So the offset wasn't exactly linear across the humidity range.

Sent from my Nexus 6 using Tapatalk

"So the offset wasn't exactly linear across the humidity range."

Yes, we call it "offset" and "slope" (or sensitivity)

You know the old saying: A physicist needs four, a mathematician three, a biologist two and a physician aficionado only one point for plotting a regression...

[earthson]

Guess that must be the Comedy-part?…

But if you believe so – fine. Saves my time of explaining it.

No offence meant, RoRo, but the only correct statement in your posts so far has been:

Please, do enlighten me. I guess things have changed since I took University Chemistry and Physics 5 years ago.

[Smallclub]

I think, and now I am speaking for someone else, what the poster meant was to use hygrometer calibration as close to the humidity that you store your cigars at. I have seen hygrometers that read 75% with a 75% boveda and 56% with a 62% boveda. This being the same hygrometer. So the offset wasn't exactly linear across the humidity range. So either make a mental note of the difference or, if the hygrometer is adjustable, adjust while using a boveda pack closer to the humidity the cigars are stored.

Thanks for the clarification. The non linear offset issue is intriguing, I must purchase a 62% boveda…

But again it shows that the $50 to $100 digital hygrometers we use in our humidors are mediocre tools…

[UpInSmoak]

Thanks for the clarification. The non linear offset issue is intriguing, I must purchase a 62% boveda

But again it shows that the $50 to $100 digital hygrometers we use in our humidors are mediocre tools

Yes that is what I essentially meant. Thanks CBMC for your input.

When I "calibrate" or set my digital hygrometer I do it in and 60 rh environment. For example setting my adjustable hygrometer at 60% Inside a humidor with 60rh beads. My margin of error is typically +or- 1 rh.

I have noticed that when I "calibrate" or set the same digital hygrometer in a salt water environment at 75rh. Example setting the adjustable hygrometer at 75% in a salt water envinroment and typically getting 75% with a deviation of +or-1. Now when I bring that hygrometer into a 60rh that deviation is much higher than +or- 1rh, sometimes as high as +or- 8. Simply put, I have found that my readings are much more accurate when I calibrate/set the hygrometer in a similar humidty environment where I intend to use it. Hope that clarifies things.

[Fugu]

Please, do enlighten me. I guess things have changed since I took University Chemistry and Physics 5 years ago.

Do I really have to?

Be assured, nothing changed in the last 5 years… perhaps just check back your scripts...

[TonyAccardo]

I think, and now I am speaking for someone else, what the poster meant was to use hygrometer calibration as close to the humidity that you store your cigars at. I have seen hygrometers that read 75% with a 75% boveda and 56% with a 62% boveda. This being the same hygrometer. So the offset wasn't exactly linear across the humidity range. So either make a mental note of the difference or, if the hygrometer is adjustable, adjust while using a boveda pack closer to the humidity the cigars are stored.

Sent from my Nexus 6 using Tapatalk

That's exactly what my hygrometer reads in my wooden humidor that has 62% bovedas in it-56%.

[fookite]

I think, and now I am speaking for someone else, what the poster meant was to use hygrometer calibration as close to the humidity that you store your cigars at. I have seen hygrometers that read 75% with a 75% boveda and 56% with a 62% boveda. This being the same hygrometer. So the offset wasn't exactly linear across the humidity range. So either make a mental note of the difference or, if the hygrometer is adjustable, adjust while using a boveda pack closer to the humidity the cigars are stored.

Sent from my Nexus 6 using Tapatalk

Exactly. But imagine the error sliding the other way: the hygrometer reads 62% in a 62% rh environment, and 72% in a 75 rh environment. If you do the salt test method like other people advocate in this thread, you are going to add a +3% offset to your hygrometer and end up storing your cigars drier than you think you are.

[Fugu]

Exactly. But imagine the error sliding the other way: the hygrometer reads 62% in a 62% rh environment, and 72% in a 75 rh environment. If you do the salt test method like other people advocate in this thread, you are going to add a +3% offset to your hygrometer and end up storing your cigars drier than you think you are.

First - this is not a problem of the salt test - this is a problem of a one-point calibration (cf. post #32). What had been matter of debate was the statement of one method being less "accurate" than the other - got the difference? And whether salts would be found in the test atmosphere....

Perhaps I will still have to explain in detail....

[earthson]

Perhaps I will still have to explain in detail....

Patiently waiting.

[Fugu]

Be moderate with the salt testing - electronic circuitry can be harmed by a saline vapor environment.

Um, upon contact with water, NaCl tends to cleave into Na+ and Cl-, both of which aerosolize readily. Hell, the NaCl will aerosolize as a complete molecule. That's why sea air has a smell - there's more than water in the air!

The salt test comes from a simpler time when people were relying on cheapo analog hygrometers. It's not terribly accurate and never has been. Boveda is the way to go for calibrating these cheap gizmos.

Ok, since there is still some debate going on, here and in other parallel threads, between using a “classic” salt-solution test and Bovedas, and some discussion and mixup of method-priciples and one- and x-point calibrations, analogue and digital/electronic, cheapo and non-cheapo instrumentation, and even some other side aspects having turned up (salty chamber-atmosphere, mixing Boveda bags etc.), I will go back and try and answer the post(s) of RoRo in more detail, which will probably address a good deal of these aspects.

As a preamble, I’d like to stress that the chances of doing the calibration wrong are likely as high or even higher than the probability that the hygrometer under testing truly is off!

Will try and do this chronologically, although some of RoRo’s statements are not necessarily relevant to the original core question, as there was:

Will salt be evaporating from the saturated NaCl-solution in the calibration chamber, and thus be potentially detrimental to an internal instrumentation (here: hygrometer)?

and additionally

Will one method (Boveda) be more “accurate” than the other (salt-solution chamber)?

Statements and my commenting as follows:

1. “…electronic circuitry can be harmed by a saline vapor environment”

There is no “saline vapor” in the test chamber. All that evaporates is water. And that exactly is an important prerequisite for the test principle being at all functional. NaCl will start evaporating in significant amounts only above its melting point (801 °C @ 1013 hPa). The sublimation pressure of the salt at room temperature practically is 0. Hence vapour pressures @ 20°C: water: 23 hPa, NaCl: 0 hPa. --> no salt evaporation from the solution. (Simplification, since the vapor pressure of H₂O in the solution will be lower - that's why we get 75.5% rH)

2. “upon contact with water, NaCl tends to cleave into Na+ and Cl-“

Salts do not “cleave”, their weak ionic bonds let them dissociate into their respective ions in aqueous solution.

3. “…., both of which aerosolize readily.”

Why should they? In the test chamber?! For forming such a salt aerosol, as mentioned in one of my previous posts, mechanical (and/or thermal) forces are needed. At sea - the example you are alluding to - the main processes being responsible for generation of salt aerosols are wind/waves and coastal surge. None of which we find in our test chamber. Neither are we boiling our solution.

4. “Hell, the NaCl will aerosolize as a complete molecule.”

NaCl is a salt (ionic bonding) not a molecule (molecular bonding). Still - won’t aerosolize nor vaporize in the test chamber.

5. “That's why sea air has a smell -…”

In my above post I asked for not confusing the chamber environment with a marine/coastal environment, where other forces come into play that make salt-solution droplets or particles become airborne. Now you come back and discuss sea air?

Right, air and in particular marine air has a smell. But not from seawater’s sodium or potassium chloride, even if they would become airborne in an aerosol. NaCl and KCl are completely odourless. What you find as a characteristic smell at sea or at the seaside are certain organic compounds, exudates, secondary metabolites from marine organisms, the most prominent of which being dimethyl-sulphide (DMS, “smell of algae”) and other often highly volatile compounds of organismic origin, and perhaps also some H₂S (intertidal, mud flats etc.). That is what we smell, but not related in any way to our test setup.

6. “…- there's more than water in the air!”

True! – and the only statement I do concur with.

7. “The salt test comes from a simpler time when people were relying on cheapo analog hygrometers.”

Several strange statements here: What exactly is a “simpler time”?! What is a “cheapo analog hygrometer”? Why “where” people relying on analogue hygrometers?

- “Cheapo analog hygrometer”

In actual fact, a mechanical analogue hygrometer (guess we are talking about the filament-tension technique using hair or artificial fibre) often is more expensive and more precise (if properly built, maintained/regenerated and calibrated) than most true “cheapo” Chinese (no offense meant) electronic ones of the capacitive (or sometimes resistive) sensor type.

Note that one of the most accurate methods still today is an analogue one: perhaps you’ve heard of the chilled mirror dew-point technique (used in most national metrology standards). And the, as well analogue, aspiration psychrometer still is the standard in official meteorological stations for measuring rH. All other electronic devices will have to be calibrated against such precision instruments and/or against primary standards.

- “The salt test comes from a simpler time”

The salt-chamber test neither is a primitive method nor “from a simpler time”, it is a primary standard. It still is and will be the most accurate fix-point test, apart from the dew-point mirror technique or psychrometer (both of which methods being less simple and much more expensive), on which calibrations of other measurement technique will be based upon and will need to be traceable to.

In metrology you need stable, reproducible primary standards, against which to calibrate your secondary standards (precision instruments – mechanical or electronic) and/or the final “consumer” instrument (”cheapo”, if you like). Those primary fix-point standards are all based on physical principles. While e.g. in temperature metrology the most important fix-points are phase transition point standards (e.g. triple point of water, melting point of gallium etc.), in hygrometry these are humidity chambers of different salt solutions (there is more than NaCl of course…). When in equilibrium, those over-saturated solutions form a very specific atmosphere with regard to relative humidity above their surface area, for a given temperature (I won’t go into further details of that here). The equilibrium water content in the air volume above the solution will be specific for each salt or a composition of different salts. This direct method of fix-points can be perfectly used without introducing an additional measurement uncertainty from any intermediate instrumentation.

8. “It's not terribly accurate and never has been.”

See above: It has always been and will be one of the most accurate and simple direct means, provided done correctly, as is holding for all methods.

9. “Boveda is the way to go for calibrating these cheap gizmos.”

Boveda is using the very same principle. Nothing new about it. What they mainly invented has been the particular packaging using a semipermeable membrane, which keeps the fluid from seeping out. And they offer a handy set of different “ready-mix” salt solutions (and some additives) allowing the user to set up a range of various equilibrium rH. You still have to observe temperature and you still have to observe a sensible relationship between surface area of the bag and air volume of your chamber/storage volume. But the statement really isn’t lacking irony, since Boveda is making use of - they adopted it - the exact same principle that is done in a salt-solution chamber, it’s no hocus-pocus. The undisputed advantage of Boveda packs is that you can do quite comfortably several measurement points and calculate a regression for the instrument to be calibrated. Disadvantage for calibration purposes is it’s more prone to small temperature variations since the equilibration time is slower and also the homogeneity of the air volume is poorer as for a salt solution chamber, with its wider, open surface. This holds in particular for instances, where the Boveda pack for calib is chosen too small compared to the enclosed air volume.

Cheers

Paul

[CUBANO]

Thanks for the post