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| Accurate cheap RH indicators? http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=32122 |
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| Author: | JoeUlman [ Fri May 06, 2011 4:01 pm ] |
| Post subject: | Accurate cheap RH indicators? |
I have an Abbeon analog hygrometer in my shop. Last year I calibrated it using some borrowed laboratory equipment. At that time I checked a couple digital thermometer/hygrometers I use to monitor a couple other rooms in my house and found their RH indications to be way off. I’d like to replace them but so far I haven’t found any cheap digital hygrometers that are accurate. Can anyone recommend an inexpensive digital hygrometer that is accurate to say +/- 5 percent? Thanks. Joe |
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| Author: | weslewis [ Fri May 06, 2011 4:16 pm ] |
| Post subject: | Re: Accurate cheap RH indicators? |
You can get a digital one at home depot for 15 bucks or so... Works just fine. |
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| Author: | woody b [ Fri May 06, 2011 7:52 pm ] |
| Post subject: | Re: Accurate cheap RH indicators? |
I supply a caliber III hygrometer with my guitars. I buy them 10 at a time, and check their accuracy with salt (75%) and potassium carbonate (43%). The most I've ever had off out of 10 is 3. I re test my personal ones every 6 months or so. |
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| Author: | Stuart Gort [ Fri May 06, 2011 8:09 pm ] |
| Post subject: | Re: Accurate cheap RH indicators? |
StewMac has a nice little one for about $25. |
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| Author: | WaddyThomson [ Fri May 06, 2011 8:52 pm ] |
| Post subject: | Re: Accurate cheap RH indicators? |
My Caliber III is a cheap piece of junk. Never within 20% of accurate. |
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| Author: | woody b [ Sat May 07, 2011 6:58 am ] |
| Post subject: | Re: Accurate cheap RH indicators? |
Zlurgh wrote: StewMac has a nice little one for about $25. It's a Caliber III. |
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| Author: | John Coloccia [ Sat May 07, 2011 7:18 am ] |
| Post subject: | Re: Accurate cheap RH indicators? |
The only one I've found that's reasonable is the Extech. http://www.testersandtools.com/Extech-4 ... 1563792333 I bought and returned about a half dozen that were absolute garbage. This one's been humming along in my shop for over two years without skipping a beat. I think you can even get a calibration "kit" for it (essentially a salt cal) so that you don't have to mess with making one yourself. If you want to spend $150, you can get the same exact meter with a NIST certificate. It really is a pretty good hygrometer. |
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| Author: | WaddyThomson [ Sat May 07, 2011 8:00 am ] |
| Post subject: | Re: Accurate cheap RH indicators? |
Something to think about! All hygrometers need to be subjected to variations in humidity to stay functional. This is particularly true of analog ones. The spring becomes set after long exposure to a constant RH, so it needs to be put in a shower or something to get it up to 100% or close, to re-set it. Then it can be calibrated to a Wet/Dry bulb or Sling Psychrometer. This recalibration should be done at least a couple of times a year. Once a quarter would probably be better. |
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| Author: | Mark Fogleman [ Sat May 07, 2011 9:57 am ] |
| Post subject: | Re: Accurate cheap RH indicators? |
About as cheap and the most accurate at normal room temps you can get. It's just not fast: http://www.flinnsci.com/documents/demopdfs/earthsci/es10301.pdf You can use it to calibrate a "Divining Stick" RH Meter to make a very reliable and relatable RH meter. John Hall gave me the idea he copied from one he saw at Thomas Jefferson's Monticello. It uses a thin cross grained Spruce/Hardwood laminate stick that bends when the RH changes. Glue one end to an index card and document where the stick is pointing when the RH is optimal, too dry and too damp. |
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| Author: | JoeUlman [ Sat May 07, 2011 3:11 pm ] |
| Post subject: | Re: Accurate cheap RH indicators? |
Thanks everyone for the replies. I ordered a pair of cheap (under $10) units I found online that have a calibration adjustment feature; something lacking in almost all the less expensive hygrometers. I’ll report back if they turn out to be any good. I’d still be interested to hear what others have to say, good or bad, about their hygrometer experiences. Joe |
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| Author: | Laurent Brondel [ Sun May 08, 2011 5:21 am ] |
| Post subject: | Re: Accurate cheap RH indicators? |
I've had good luck with the Caliber III hygrometers, no more than 1% variation between different ones. |
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| Author: | nickton [ Sun May 08, 2011 1:22 pm ] |
| Post subject: | Re: Accurate cheap RH indicators? |
don't know if mine is any good. It's an EXTECH brand digital model 445814 made in china, with reset instructions in the back for high and low humidity. I just put a battery in and stuck it on the wall. It has temp, dewpoint, and relative humidity. I hope it's accurate enough. 
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| Author: | JoeUlman [ Mon Jun 06, 2011 9:22 am ] |
| Post subject: | Re: Accurate cheap RH indicators? |
Update: Just thought I’d report back on the cheap analog hygrometers I picked up last month. They are small brass humidor hygrometers with a calibration screw in the back and come with a magnetic mount. I think I paid about $8 each from Amazon. Out of the box they were no where near accurate (almost 20% off initially). After exercising them between 30% and 95% [edit: by this I mean I placed them in a 95% RH (damp towel) environment for several hours, then into a 30% RH room for several hours and back to 95% RH] and a few calibration sessions over several days they showed surprising accuracy in the 40% to 50% range (final calibration was at 45%). They tend to read slightly high at RH over 50% and slightly low below 40% but seem pretty accurate between 40% and 50%, at least for the three weeks or so since calibration. Attachment: IMG_1866 copy.jpg For those interested, I calibrated using a Cole Parmer digital hygrometer which I checked against a sling psychrometer. Joe |
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| Author: | Andy Birko [ Mon Jun 06, 2011 11:12 am ] |
| Post subject: | Re: Accurate cheap RH indicators? |
Filippo Morelli wrote: Search forum. Several good threads. C'mon man, you can do better than that. Here's a link to a test that Hesh did a while back: viewtopic.php?f=10101&t=27087&p=364087&hilit=andy+birko+caliber#p364087 I brought over my caliber III at a different time and it tested dead nutz accurate compared to the psychrometers. I ended up buying a psychro-dyne on e-bay for like $25 though just for peace of mind. |
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