Humidity and hygrometers

Discussion in 'Setup & Repair [DB]' started by drurb, Jan 7, 2014.


  1. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC Supporting Member

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    It's that time of year again. This post got me curious:
    Edit-- The instructions linked below are reproduced here in post #4 of this thread.

    Here's a link to a nice set of instructions for doing the "salt test." You can do the test with just about any hygrometer and note the error. If you want a hygrometer that you can calibrate, here's a nice little one.



    Some of us obsess about maintaining proper humidity. The hygrometers most of us end up with can be pretty far off.
  2. carl h.

    carl h.

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    nice link!
  3. fdeck

    fdeck Supporting Member

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    Thanks for the link on the hygrometer. I've used the wet/dry bulb technique, but it's a hassle to set up, and the electronic version seems convenient.
  4. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC Supporting Member

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    I reproduced the instructions below from this post. The original site can take a bit of time to load. Kudos to Tman at puff.com.

    How to do a salt test

    This is how I do my salt test. Salt has an amazing property where RH% will be pretty much nearly be 75% when it is in a saturated condition with water.
    (Look for Sodium Chloride, aka. Salt)
    http://www.omega.com/temperature/z/pdf/z103.pdf

    Here's what you'll need:
    Salt (I use Morton Salt)
    Small Ziploc© Bag (Small as possible)
    Bottle cap (Gatorade cap works best. Wide&shallow works best. I'll use water bottle cap for this)
    Toothpick (whatever to mix the salt)
    Hygrometer to be calibrated

    [​IMG]

    First, put salt in the bottle cap

    [​IMG]

    Then, put couple drops of water in the salt. Notice it's partially wet. You want the salt to suck up all the water.

    [​IMG]

    Mix the salt/water mix so it will be a good mix.

    [​IMG]

    Once you have the saturated salt, put it into a Ziploc bag with your hygrometer. Pinch up the center of the Ziploc bag so it will inflate the bag. While you are doing this, seal the bag with your other hand. The bags should be inflated so it won't cover the sensor opening of the hygrometer or the bottle cap.

    [​IMG]

    Give it couple of hours for the RH% to stabilize. I think 6 hours should be sufficient time to do this.

    [​IMG]
    Once the RH% stabilizes, calibrate your hygrometer within the Ziploc bag. On HygroSet, I'll have to twist the dial (clockwise for +RH% and counter-clockwise for -RH%. Press the Set button.)

    On Xikar hygrometer, press "Calibrate".

    It might be easier to use a tip of a pen to press the button. If you want, you can leave the bag for another 6 hours and make sure the reading stabilizes at 75%.

    That's it! Enjoy your calibrated hygrometer!
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  6. fdeck

    fdeck Supporting Member

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    Thanks!
  7. fdeck

    fdeck Supporting Member

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    Amazing, somebody is selling a "one step hygrometer calibration kit" on Amazon. And guess what... it maintains a constant humidity of 75 percent.
  8. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC Supporting Member

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    Yes, the cigar aficionados are really into this. I did a bit of reading in their forums. The word is that the DIY method is just as good as the kits because they functionally contain the same materials. The instructions that I reproduced are the best of the many sets I found. It turns out to be somewhat essential to stir the salt/water mixture.

    Happy experimenting!
  9. ErikvanD

    ErikvanD

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    Nice to see a quote of one of my postings starting a new thread :D
    This is the YouTube video I used:



    It is essentially the same but now on video. And with a plastic box instead of a bag.

    Happy calibrating!
  10. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC Supporting Member

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    Thanks for getting me started on all of this! I saw that video as well. As I mentioned earlier, after playing around with this several times, it seems that adding a small amount of water to the salt and stirring to achieve the consistency and texture shown in the pics above does make a difference. Also, the use of a ziplock bag allows calibration without removing the hygrometer.

    Anyway... thanks again. :)
  11. robobass

    robobass

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    Fascinating that there is such a simple solution(pun intended) to hygrometer calibration. I would point out however that just because your hygrometer is accurate at 75% doesn't mean the same is true at 40%. I wonder if there's a way to test accuracy at lower humidity. I'm lucky that where I live humidity is a non-issue. My apartment never dips below 40%, and the handlers in my former orchestra leave basses and cellos on the truck overnight in sub-freezing weather all the time. As unpleasant as it is to warm up a chilled bass before a morning rehearsal, temperature cracks and open seams occur only very rarely.

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