Robbie,
"Then go to this site and choose the correct feet above sea level ..."
Here in Florida...we are below sea level...
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| make your own sling hygrometer http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=14005 |
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| Author: | Robbie O'Brien [ Thu Oct 11, 2007 8:58 am ] |
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This is a follow up on the recent thread about RH I came across some info today on the web that will teach you how to make your own sling hygrometer. What is this you ask? Well, to accurately find the RH in your shop it is necessary to measure the dry temp and the wet temp and then find the difference between the two. Then use a chart to find the precise RH. I spent 5 bucks today on two thermometers and then found an online US weather RH table and viola!! I have accurately measured the RH in my shop. Go to this site for instructions on how to make a sling hygrometer. http://asd-www.larc.nasa.gov/SCOOL/psychrometer.html Then go to this site and choose the correct feet above sea level table for your area and follow the instructions on how to read it. http://www.wrh.noaa.gov/sto/rhtbl.php Give it a shot and let everyone know how it went. Of course, you could just spend some big bucks and get a hygrometer that is accurate to +/- 3% then you can just forget about this hole mess! |
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| Author: | BlackHeart [ Thu Oct 11, 2007 11:55 am ] |
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What about Horse Hair hydrometers? |
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| Author: | Dave-SKG [ Thu Oct 11, 2007 12:28 pm ] |
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Robbie, "Then go to this site and choose the correct feet above sea level ..."
Here in Florida...we are below sea level... |
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| Author: | Bruce Dickey [ Thu Oct 11, 2007 12:44 pm ] |
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http://asd-www.larc.nasa.gov/SCOOL/psychrometer.html Nasa Link - Roll Your Own http://www.wrh.noaa.gov/sto/rhtbl.php Nasa Link to Chart at your elevation |
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| Author: | Steve Walden [ Fri Oct 12, 2007 3:19 am ] |
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[QUOTE=Dave-SKG] Here in Florida...we are below sea level... [/QUOTE] Hey! Thats my line!!! |
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| Author: | Bruce Dickey [ Fri Oct 12, 2007 4:17 am ] |
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Sling hygrometers won't work under water.
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| Author: | WaddyThomson [ Fri Oct 12, 2007 4:55 am ] |
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Yeah, and homemade ones don't work all that well either. I tried that, but the thermometers are not stable enough. They can't maintain temperature in the sling process, even if you do it very slowly. I find that the dry thermometer looses somewhere in the 3 - 4* range in the process of getting the wet bulb thermometer down to a stable temp. In that case, do you use the original temp or the reduced temp of the dry bulb as a figuring point? I think it takes a pretty high price, commercial, thermometer to maintain temp with the centrifugal force trying to lower it. |
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| Author: | Bruce Dickey [ Fri Oct 12, 2007 7:36 am ] |
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Waddy, I was wondering why the dry thermometer needs slinging at all? Looks like you could sling one thermometer wet and match it to a static mounted one and find the difference. Okay you scientists, what's the deal here? |
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| Author: | WaddyThomson [ Fri Oct 12, 2007 8:20 am ] |
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I don't know either. I have actually seen some wet bulb hygrometers which have reservoirs for the wet bulb, and a wick, and they just sit stationary, with no spinning. Maybe that's the best way. Then there is no outside influence on either thermometer other than evaporation of moisture. |
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| Author: | Robbie O'Brien [ Fri Oct 12, 2007 9:23 am ] |
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It is not necessary to sling them. You can just place a fan in front of them. The idea is to move air across the wet bulb so that it evaporates the water in the cloth wrapped around the end of the thermometer |
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| Author: | Todd Rose [ Sun Oct 14, 2007 8:25 am ] |
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Thanks for the tip, Robbie. I can't get to that web site, unfortunately ("Firefox can't find the server"). I'll try again later. Is anyone else having this problem? |
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| Author: | Todd Rose [ Mon Oct 15, 2007 10:24 pm ] |
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Never mind. It worked for me this time. Thanks again, Robbie. |
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| Author: | Bruce Dickey [ Tue Oct 16, 2007 1:53 am ] |
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I just printed off my copy of Nasa's RH and DewPoint Scale for under 500 feet above ground level. Looking at 77 degrees F dry and 77 degrees F wet, the intersection yields 100 percent Relative Humidity, equilibrium. Now my theory: Since my shop is air conditioned it stays at 77 degrees year round. I just need one thermometer with gauze and water on it, and a tiny breeze, right? Theoretically at least, ay? I should be able to post one wet bulb thermometer and get the RH from the differences in the two readings. Okay, first I find out of the two thermometers, the digital wall unit tied to the AC and the static standard thermometer. Should work, First I have to find a thermometer. I'll let you know how it comes out and how it agrees with my digital hygrometer I thought was gospel until you slingers came along....
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| Author: | WaddyThomson [ Tue Oct 16, 2007 3:15 am ] |
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Everyone has to sling a little psychrometer sometime!  
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| Author: | Bruce Dickey [ Tue Oct 16, 2007 3:32 am ] |
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Waddy, if you take out two letters it's: Everyone has to sing A Little PSYCHO Meter Some Time!
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| Author: | grumpy [ Thu Oct 18, 2007 1:53 am ] |
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a) go buy a good thermometer. b) write down the room temperature c) Tie a wet gauze around the thermometer's bulb. d) fire up the dust collector, and place the wet gauze directly in the air stream entering a hose tot eh dust collector. e) wait for the temperature top stabilize f) write down the temperature. g) using a readily available and printable chart from the internet, find your RH As accurate as any device known. The only thing to watch for is to have enough air flow. You know when you have enough by trying various amounts and velocities until the temperature no longer drops. By using a vacuum or dust collector to _pull_ air past the wet bulb, you are assured that the air is the ambient room air. If you used a fan to blow air across the bulb, the air is heated slightly by the fan blades and motor, thus screwing the readings..... Total cost? less than 10 clams for the scientific/lab thermometers(always use pairs if you're paranoid <g>). It will last forever, and never need calibrating. |
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| Author: | WaddyThomson [ Thu Oct 18, 2007 1:59 am ] |
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Welcome Home Grumpy! How was the Race? 
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| Author: | grumpy [ Thu Oct 18, 2007 2:08 am ] |
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Loud.... 
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| Author: | WaddyThomson [ Thu Oct 18, 2007 2:11 am ] |
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Interesting, that's what I remember about the only race I ever attended. We sat in the last turn before the finish line, about 5 or 6 rows back. Should have had ear protection and dust masks. We were covered in black rubber dust. 
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| Author: | grumpy [ Thu Oct 18, 2007 7:51 am ] |
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I meant, loud, in a good way <bg> Hearing protection is mandatory. hearing loss is a sure thing for those who go unprotected. The whole thing was quite incredible, and more than I expected. |
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| Author: | Bill Bergman [ Thu Oct 18, 2007 10:41 am ] |
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Periodically I see old surplus US Forest Service sling psycrometers on ebay. I would recommend to NOT buy those, as I believe that they have mercury in the bulbs. You don't want to take the chance of slinging one around and breaking the bulb, scattering mercury around your shop. |
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| Author: | Todd Rose [ Fri Oct 19, 2007 1:29 am ] |
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[QUOTE=grumpy] a) go buy a good thermometer.b) write down the room temperaturec) Tie a wet gauze around the thermometer's bulb.d) fire up the dust collector, and place the wet gauze directly in the air stream entering a hose tot eh dust collector.e) wait for the temperature top stabilizef) write down the temperature.g) using a readily available and printable chart from the internet, find your RHAs accurate as any device known. The only thing to watch for is to have enough air flow. You know when you have enough by trying various amounts and velocities until the temperature no longer drops. By using a vacuum or dust collector to _pull_ air past the wet bulb, you are assured that the air is the ambient room air. If you used a fan to blow air across the bulb, the air is heated slightly by the fan blades and motor, thus screwing the readings.....Total cost? less than 10 clams for the scientific/lab thermometers(always use pairs if you're paranoid <g>). It will last forever, and never need calibrating.[/QUOTE] Mario, thanks for boiling this down to the essentials. |
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