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| Hygrometer Calibration http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=53035 |
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| Author: | Toonces [ Mon Mar 23, 2020 2:22 pm ] |
| Post subject: | Hygrometer Calibration |
I think most of you all know how to calibrate your hygrometers. I like to calibrate with a Potassium Carbonate salt test - super easy and foolproof - perfect for me because I'm not very bright. A lot of players are concerned about the accuracy of their hygrometers and so I made a tutorial of the process. Here's a link if you've never done one before: http://fayguitars.com/Guitars/hygrometer.html If you are at the point where you are selling your guitars, then you want to maintain tight reigns on your shop humidity. Or at least, keep the environment tightly controlled at specific key points of the build process: gluing the top/back braces, gluing the plates to the sides, and gluing the bridge. |
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| Author: | jfmckenna [ Mon Mar 23, 2020 3:04 pm ] |
| Post subject: | Re: Hygrometer Calibration |
I shooed try that some day. For years I've been calibrating mine with one of those psycrodyne Hygrometers but it would be interesting to see how accurate that is. |
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| Author: | J De Rocher [ Mon Mar 23, 2020 9:52 pm ] |
| Post subject: | Re: Hygrometer Calibration |
Thanks for posting your tutorial. I've been using the potassium carbonate method that was posted on the ANZLF in 2014 for several years now. http://www.anzlf.com/viewtopic.php?t=6123 It's interesting to me that the two methods give instructions for preparing the saturated potassium carbonate that appear to be basically opposite of each other and yet they both work. Your method calls for a slurry of potassium carbonate in water which ends up producing a layer of clear water on top of undissolved potassium carbonate. The method posted on the ANZLF calls for wetting the potassium carbonate with an amount of water that leaves no free water. I'm puzzled by this but not enough so far to crack my college chemistry books or google for info on equilibrium between a salt/water mixture and air. Maybe at some point I'll check my hygrometers using both methods and see how the readings compare. I would have to buy more potassium carbonate though because quite a bit more of it is needed for your method. |
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| Author: | Toonces [ Tue Mar 24, 2020 1:30 am ] |
| Post subject: | Re: Hygrometer Calibration |
They can both work BUT you can add too little water. The idea is to have enough water in the container to effect the environment of the container. If you dampen an amount of salt that is appropriately sized for your container and make sure the salt is really "wet", then you are golden. However, it is also possible to put some salt in there and add a few drops of water and then you probably aren't going to get accurate results. In scientific terms, you are creating "saturated" solutions with both scenarios -- the way I do it tho' ensures you have enough "solution" to effect the container's environment in a timely manner. Both methods work but my method is foolproof - the other isn't, which is why I recommend that folks just do it this way instead. |
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| Author: | jfmckenna [ Tue Mar 24, 2020 8:25 am ] |
| Post subject: | Re: Hygrometer Calibration |
IIRC the chemical term for it is a suspension. Next in line to that would be a colloid which is a solution that has undissolved particles in it but they are too small to see with the eye. Followed by simply a solution which would be a percentage of the dissolved stuff in it. The suspension settles out and could probably be called a colloid at that point. The suspension guarantees that the solution is saturated which yields the proper result. But I only minored in chemistry so I could be wrong 
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| Author: | Toonces [ Tue Mar 24, 2020 10:26 am ] |
| Post subject: | Re: Hygrometer Calibration |
It's been a while since I've graduated (Biochem major) - but generally, I always remember those terms were applied to scenarios where there was liquid present. You work with a lot of suspensions in organic chemistry along with aqueous and non-polar components and precipitates. I may be absolutely wrong on this but I believe colloid is the description of the milky saturated solution in my pictorial. Lots of tiny particles that settle out of the solution after a time. But you have a large liquid phase present. This may be your area of expertise jm -- I'd be curious if there is a specific chemistry term for what might be equivalent to wet sand. I imagine there is a specific term to describe having a material that is just slightly dissolved with a solvent. I'm thinking that it is equivalent to the sand scenario where the liquid would be saturated aqueous solution that is suspended in salt -- basically, it's kind of like mud. Anybody that can set us straight on the proper terminology? |
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| Author: | Barry Daniels [ Tue Mar 24, 2020 10:31 am ] |
| Post subject: | Re: Hygrometer Calibration |
A sling psychrometer is quicker and easier. My cheap-o plastic version is probably not real precise but +/- 1 to 2% is not a problem for my requirements. The good thing for me is no chemistry degree is required. When I bought this 20 years ago it was only $25. Unfortunately it has gone up a bit. https://www.amazon.com/Carolina-Biological-Supply-Company-Psychrometer/dp/B007VCNG5G/ref=sr_1_22?crid=G67T54MHDCAD&keywords=sling+psychrometer&qid=1585063704&sprefix=sling+psy%2Caps%2C179&sr=8-22 |
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| Author: | Toonces [ Tue Mar 24, 2020 10:56 am ] |
| Post subject: | Re: Hygrometer Calibration |
Sling psychrometers rely on accurate thermometers - and you'd be surprised how often they aren't accurate. To be honest, I always found them super finicky - maybe I wasn't working with a good one. The salt test is simple to set up (5 minutes tops) and will give perfect, foolproof results every time. It definitely is not as quick as using a sling psychrometer but I want to calibrate my hygrometers to be accurate within 1% point. It is also important to note that room humidity can vary quite a lot depending on where you are in the room -- the salt test completely eliminates this massive variable. In my particular house (in Florida), I would have to wait for a specific day where no humdifiers/dehumidifiers are running and the RH readings are very stable before I would put any faith in a sling psychrometer calibration. I think those of us that have to manage our environments (dehumidification/humidification) will absolutely find the salt test is far more convenient. Just my opinion tho' - everybody should choose what they feel most comfortable with. |
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| Author: | doncaparker [ Tue Mar 24, 2020 11:19 am ] |
| Post subject: | Re: Hygrometer Calibration |
Toonces wrote: Sling psychrometers rely on accurate thermometers - and you'd be surprised how often they aren't accurate. To be honest, I always found them super finicky - maybe I wasn't working with a good one. The salt test is simple to set up (5 minutes tops) and will give perfect, foolproof results every time. It definitely is not as quick as using a sling psychrometer but I want to calibrate my hygrometers to be accurate within 1% point. It is also important to note that room humidity can vary quite a lot depending on where you are in the room -- the salt test completely eliminates this massive variable. In my particular house (in Florida), I would have to wait for a specific day where no humdifiers/dehumidifiers are running and the RH readings are very stable before I would put any faith in a sling psychrometer calibration. I think those of us that have to manage our environments (dehumidification/humidification) will absolutely find the salt test is far more convenient. Just my opinion tho' - everybody should choose what they feel most comfortable with. I completely agree with this. I own an old psychrometer, and I do not trust its thermometers any longer. My potassium carbonate tests (conducted just like Toonces) are more reliable. Chasing accuracy when it comes to RH management is harder than it ought to be! |
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| Author: | Ruby50 [ Tue Mar 24, 2020 1:42 pm ] |
| Post subject: | Re: Hygrometer Calibration |
Always within 5% of my industrial unit, plus it's easy to read from across the room. I'm an amateur and probably would do more if I was selling a bunch of instruments Ed |
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| Author: | wbergman [ Tue Mar 24, 2020 5:29 pm ] |
| Post subject: | Re: Hygrometer Calibration |
Just don't use an old sling that has mercury thermometers. Supposedly if you break them and scatter the mercury, you have problems. That said, I used to have a jar of mercury as a kid that I played with, and so far I am not dead. |
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| Author: | J De Rocher [ Tue Mar 24, 2020 5:45 pm ] |
| Post subject: | Re: Hygrometer Calibration |
wbergman wrote: Just don't use an old sling that has mercury thermometers. Supposedly if you break them and scatter the mercury, you have problems. That said, I used to have a jar of mercury as a kid that I played with, and so far I am not dead. Hah! I remember playing with beads of mercury on the bathroom floor when I was five after a thermometer broke. Which reminded me of this photo that has stuck with me since I saw it in National Geographic when I was a kid. This guy is floating on a pool of mercury. Ack! Attachment: floating on mercury.jpg
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| Author: | bluescreek [ Wed Mar 25, 2020 7:25 am ] |
| Post subject: | Re: Hygrometer Calibration |
we used to get mercury in gilbert chemistry sets. Played with it coated copper pennies that and asbestos yup great childhood |
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