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Author Topic: Accurate (and cheap) digital hygrometer in calibration bag photo  (Read 1983 times)
rikstar
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« on: May 01, 2011, 02:00:09 AM »

How about this accuracy for a $19 digital hygrometer... right on the money!! I was pleasantly surprised by this because I was under the impression that analog hygrometers were superior. I hope it stays this accurate forever. It's called the  "Caliber III Thermometer Hygrometer" (on Amazon) and mine is about 6 months old now. I thought about getting a nice analog device but the good ones are not cheap so I decided on this one.  The calibration device in the photo is pretty cool and also cheap - about $3. It consists of a mini humidipak which is set to create 75% humidity in a ziplock bag. You simply insert your hygrometer into the bag and let it sit for 24 hours and see if it reads 75%. If your hygrometer does not read correctly, just add or subtract the % points that your device is off by when making your readings. Or toss it and buy one of these.
 

Rick

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Rick

2009 Larrivee L-10e
1999 Larrivee D-02e
2004 Ovation Elite T
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"There’s only two kinds of music: the blues and zippity-doo-dah.”-Townes Van Zandt
rikstar
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« Reply #1 on: May 01, 2011, 02:13:20 AM »

I posted this picture on Amazon as part of my product review... just FYI, so if you go there and see it, you won't wonder why the same pic is on Amazon cop.
Rick
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Rick

2009 Larrivee L-10e
1999 Larrivee D-02e
2004 Ovation Elite T
2000 Yamaha SG 500B

"There’s only two kinds of music: the blues and zippity-doo-dah.”-Townes Van Zandt
ark
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« Reply #2 on: May 01, 2011, 03:56:07 AM »

I have the same hygrometer and have found it to be fairly accurate.  However, I sure wish some clever person would come up with a "guitar friendly test kit" that works at 45% (instead of 75%) humidity because the accuracy of these relatively inexpensive digital hygrometers typically varies over their measurement range.  Thus it could read 5% high at 75% humidity, and 5% low at 45% humidity.
Al
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rikstar
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« Reply #3 on: May 01, 2011, 04:21:19 AM »

That is a very good point. I didn't think of that. I went back and read the reviews on this. Most are good- great but some are really bad... Maybe a batch of defective devices got through. I use the humidipaks for guitars by planet waves and in my case, my caliber III reads 40-50 ish most of the time depending on how dry it is in the room. I guess one could use those packs as calibration kits by placing them in a ziplock bag with the device.
Rick
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Rick

2009 Larrivee L-10e
1999 Larrivee D-02e
2004 Ovation Elite T
2000 Yamaha SG 500B

"There’s only two kinds of music: the blues and zippity-doo-dah.”-Townes Van Zandt
jandrew
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« Reply #4 on: May 01, 2011, 04:46:19 AM »

I have the same hygrometer and have found it to be fairly accurate.  However, I sure wish some clever person would come up with a "guitar friendly test kit" that works at 45% (instead of 75%) humidity because the accuracy of these relatively inexpensive digital hygrometers typically varies over their measurement range.  Thus it could read 5% high at 75% humidity, and 5% low at 45% humidity.
Al

Indeed. I've seen response curves for similar capacitance sensors (dew point in this case) and they are generally non-linear s shaped curves ... so you could easily have a sensor in a hygrometer that reads 3% low at 75% and 3% high at 40% and still be within a +/- 3% error limit --- But, if you did a salt test at 75% on such a unit and noted that it was 3 points low and decided to always 3 points to the reading and were trying to maintain a 40% level, you'd let the unit go to 37% (cause you're adding 3), but its at the top of its error curve and the humidity is only 34%.

An inexpensive way to double check relative humidity is with a wet bulb/dry bulb psychrometer -- which can be easily improvised as shown here:

http://www.miamisci.org/hurricane/psychrometer.html

cheers,
andrew
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Andrew J.
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« Reply #5 on: May 01, 2011, 07:35:13 AM »

Jandrew,
I'm glad you brought up the use of a real wet bulb/dry bulb phsychrometer into the discussion. The absolute best way to determine the true RH of any environment is to use 2 identical (must be accurate) thermometers.  I was in the forest fighter business for 35 years and the unquestionably most accurate way of measuring RH is to compare the temps. of 2 identical thermometers.  One of the two will have a wick of cotton soaked in water surrounding the bulb at the bottom (called the wet thermometer) and the other one (called the dry bulb) will have no such wetting.  To determine the RH you push air over both thermometer's bulbs at the same time for a minimum of 3 minutes with a fan or by twirling the two together in a special holder.  You then record the difference in temperature between the two and consult a chart to determine the RH.
Since I happen to have this equipment in my possession ( I didn't turn it in when I retired), I use it to check the accuracy of my digital hygrometers.  I find that both the built-in hygrometer in my cheap humidifier and my supposedly more accurate digital hygrometer read too low compared to the actual humidity determined by the more accurate method of using the thermometers.  I take this into consideration when I'm trying to figure out what the true humidity around my guitars is.  Knowing that my digital devices are reading low, I just use their readings as my guide to adjust humidity levels, thinking that if they are wrong, a little extra RH is a bonus,  Hopefully this makes sense.

Kurt
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