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Thread: Digital Hygrometer vs Hygrometer on Dry Cabinet

  1. #1
    vince123123
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    Default Digital Hygrometer vs Hygrometer on Dry Cabinet

    Hi there! Does anyone have this problem? Basically I just bought a new digital hygrometer and put it inside the dry cabinet. Horror to horrors, I discovered that hte two has a difference of at least 10%. WHat showed on my Dry cabinet as 50% is now 40% on my digital hygrometer

    Does anyone experience hte same problem as me? Now im not sure which one is spoilt...or is any even spoilt

    PS I have left both to "settle" before taking any readings, in view of the fact that digital is much faster in response to the analogue dry cabi meter

  2. #2
    Moderator ziploc's Avatar
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    That is quite "normal". My experience is that the hygrometers that came with dry cabinets are normally not properly calibrated. When I bought my dry cabinets, I actually found a difference of 20%. Just calibrate your dry cabinet's hygrometer yourself with a screw driver to match the digital one.

  3. #3

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    What makes the digital hygrometer any more accurate than an analog one? Don't trust a digital one just because it can show figures with decimal points.

    You can calibrate a hygrometer yourself using a salt test. It is described here (taken off a website):

    Fill a bottle cap with a teaspoon of salt and moisten with a few drops of_water._ Make a paste, not a saline solution. Place the bottle cap along with the hygrometer in a Ziplock bag and seal it up._ Let it stand for about 6 hours then check the humidity level._ It should read 75%._ If not, you can adjust most analog hygrometers with a screw on the back of the unit._ However, some hygrometers donít have an adjustment screw so youíll just have to note the difference and apply it when you check your humidity level in the future.

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    Moderator ziploc's Avatar
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    Originally posted by reflecx
    What makes the digital hygrometer any more accurate than an analog one? Don't trust a digital one just because it can show figures with decimal points.
    I never say digital ones are more accurate just "because it can show figures with decimal points". Digital ones are more accurate because they are sold as an individual product and as a measure instrument they are properly calibrated when they leave the factory.
    Last edited by ziploc; 16th May 2003 at 01:22 PM.

  5. #5

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    Originally posted by ziploc
    I never say digital ones are more accurate just "because it can show figures with decimal points". Digital ones are more accurate because they are sold as an individual product and as a measure instrument they are properly calibrated when they leave the factory.
    By the way, where can I purchase a digital hygrometer? THe analog hygrometer that comes with my dry cabinet is also behaving erratically. Without opening the door at all, at one time it can show 45% RH, and few hours later it can show 60% RH.. very scary leh...

    TM

  6. #6
    Moderator ziploc's Avatar
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    Originally posted by trendmatrix
    By the way, where can I purchase a digital hygrometer? THe analog hygrometer that comes with my dry cabinet is also behaving erratically. Without opening the door at all, at one time it can show 45% RH, and few hours later it can show 60% RH.. very scary leh...

    TM
    Hmm... could it be the weather changes that caused the fluctuation? Anyway, you can get the digital one at most hardware stores e.g. homefix, etc.

  7. #7

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    Originally posted by ziploc
    Hmm... could it be the weather changes that caused the fluctuation? Anyway, you can get the digital one at most hardware stores e.g. homefix, etc.
    Oh okay thanks... anyway how much is it?

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    Originally posted by trendmatrix
    By the way, where can I purchase a digital hygrometer? THe analog hygrometer that comes with my dry cabinet is also behaving erratically. Without opening the door at all, at one time it can show 45% RH, and few hours later it can show 60% RH.. very scary leh...

    TM
    Check if the doors are not leaking.........

    Hong Sien

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    Originally posted by ziploc
    I never say digital ones are more accurate just "because it can show figures with decimal points". Digital ones are more accurate because they are sold as an individual product and as a measure instrument they are properly calibrated when they leave the factory.
    I am not very sure if they are ALL calibrated, they are likely to be calibrated at random in the production line. With ALL mering devices you can never be sure if they are calibrated properly unless it is stated.

    Hong Sien

  10. #10

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    Originally posted by hongsien
    Check if the doors are not leaking.........

    Hong Sien
    Sorry hah... i very blur... how do i check if the door is leaking leh?

  11. #11
    esther
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    Originally posted by trendmatrix
    By the way, where can I purchase a digital hygrometer? THe analog hygrometer that comes with my dry cabinet is also behaving erratically. Without opening the door at all, at one time it can show 45% RH, and few hours later it can show 60% RH.. very scary leh...

    TM
    Had problem with dry-box too. Got mine at Sim Lim Square (the shop on the left of escalator at the basement, going toward to foodcourt) for about $15-18(can't remember the exact figure).

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    think that u can get one for ard $20 at rubyat penisula opposite camera workwork.

    leaking door? thats a good one, i dunno how to check either.
    therotically if u dun open it, humdity should not change or very minimal once it has settled down rite? try not opening door for a few days and see if it climbs?

  13. #13

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    Originally posted by ziploc
    Digital ones are more accurate because they are sold as an individual product and as a measure instrument they are properly calibrated when they leave the factory.
    That would seem logical, but going by logic, dry cabinet humidity level also very important, shouldn't the dry cabinet manufacturer ensure that the installed hygrometer is properly calibrated too?

    Well, if we know that cheap dry cab hygrometers are not calibrated properly, what makes you think that cheap digital hygrometers will be?

    Fact is, do the salt test and calibrate it yourself.

  14. #14
    vince123123
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    THe salt test itself looks rather variable. For e.g., doesn't the amt of water put into it affect the results? Second and more importantly doesn't the size of hte ziploc affect as well?

  15. #15

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    Originally posted by vince123123
    THe salt test itself looks rather variable. For e.g., doesn't the amt of water put into it affect the results? Second and more importantly doesn't the size of hte ziploc affect as well?
    Just make the salt damp, don't make saline solution. We want to make sure the salt solution is saturated. The salt and air will then reach equilibrium after a few hours, and the resultant humidity is 75%.

  16. #16
    Moderator ziploc's Avatar
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    Originally posted by reflecx
    That would seem logical, but going by logic, dry cabinet humidity level also very important, shouldn't the dry cabinet manufacturer ensure that the installed hygrometer is properly calibrated too?

    Well, if we know that cheap dry cab hygrometers are not calibrated properly, what makes you think that cheap digital hygrometers will be?

    Fact is, do the salt test and calibrate it yourself.
    Well, in that case you better send it to SISIR for calibration.

  17. #17
    Moderator ziploc's Avatar
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    Originally posted by hongsien
    I am not very sure if they are ALL calibrated, they are likely to be calibrated at random in the production line. With ALL mering devices you can never be sure if they are calibrated properly unless it is stated.

    Hong Sien
    Yes they are all calibrated if they are to be sold as a measuring instrument.

  18. #18

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    before you take a reading off your analog meter, give it a slight knock

    serious, you'll see some difference....
    36frames Wedding Photography - http://www.36frames.com
    rueyloon - http://www.rueyloon.com

  19. #19
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    Originally posted by rueyloon
    before you take a reading off your analog meter, give it a slight knock

    serious, you'll see some difference....
    Yeah, most of the time, the needle "sticks".

    Regards
    CK

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