*
Alan:
A year or so ago Don Fugler of Canada Mortgage and Housing Corporation did a study of hygrometer precision. He found that the $30-$40 units (Radio Shack for example) were within +/- 5%RH provided they were not subjected to extreme dryness or wetness, and the environment was somewhat clean. It’s best to ask to see a bunch of them at the store and take one that is reading in the mid-range, in order to not buy an outlier. The instrument will drift after a year or two. For homeowners, Fugler concluded, a $30 instrument is a good buy.
Sling psychrometers generally give readings that are erroneously high, because the operator doesn’t do enough slinging, and because of water impurities. Mechanically aspirated psychrometers with distilled water give good readings. But to convert the resulting wet bulb temperature to RH requires a precise (dry bulb) temperature reading. The error that results from these two instrument errors is probably still below the +-5%RH error in the cheaper instruments.
Greater precision than +-5% costs more, and requires more frequent factory calibration. Vaisala makes instruments that many researchers consider the best, and they have a range from $hundreds to $thousands. The “gold standard” for humidity measurements uses a chilled mirror dew point sensor ($3000).
Fugler report at:
http://www.cmhc-schl.gc.ca/cmhc.html
Replies
*
I have several inexpensive humidity/temperature gauges in the house.
You know, the kind with two dials in a plastic wood tone case that you place on a desk/counter/shelf.
I glance at them at least several times/day to either check the temperature or humidity level in different areas of the house.
I noticed when I purchased them the readings were not consistant among them in their display packages - some were off by quite a large margin.
In searching for a reasonably priced and accurate gauge that measures relative humidity I've noticed there isn't any sort of standard of accuracy.
Can you recommend a source for quality gauges in the $30 - $100 range ?
I'm particularily interested in getting accurate readings in the basement where I try to maintain 50% or less RH during the warm season.
I have seen in various catalogs those fancy looking brass gauges in both analog and digital types. But once again, how can you tell if they will give accurate readings ?
Thanks for your help.
*You can get good ones, either digital or analog, at a cigar store.
*I purchased a digital gauge at the BIG NASTY ORANGE BOX(home depot), IT SEEMS to be fairly accurate. For higher quality check with you local HVAC distrubutors.David
*You can't trust any inexpensive hygrometer, IMO (and speaking from some experience making humidors). I make it perfectly clear to humidor customers that they will give you a ballpark only, and if you are lucky. As a test, I've kept five identical hygrometers, purchased at the same time, side by side in the same room, and 20-30% variance can be expected on a good day. The digital ones are no better, at least in the lower price ranges.Depends how far you want to go with this; I don't know what they cost, but when I worked in museum conservation, we used sling hygrometers for quick reads (you swing it round and round like a sling shot), and for real accuracy, we used recording hygrothermographs-measure temperature and humidity. They may cost a fortune, I've never bought one, but suppliers to museums and conservators would have them.
*Grainger has the $100 digital ones. NEver checked mine against anybody elses so maybe it's wrong. Davis Instruments makes the $3,000 ones if that's what you want.
*Thanks so much for the suggestions.I would have never thought of checking with the local cigar store - great idea.I will also check with all other sources suggested.We do have a new Home Depot opening this month and I have access to a Graingers catalog.And now that you mention it, Adrian, I do recall hearing about the sling hygrometers or maybe seeing one in action on a TV program.If it gives accurate readings I'm willing to shell out some $ for a couple of gauges - but maybe not in the thousands....
*I would have suggested Grainger's too -- theoretically they don't sell to the public? -- see http://www.grainger.com. They have the sling thingies too -- "psychrometers" technically.Standard "accuracy" for cheapies appears to be +/- 5%, not very good. But i suppose you could get one nice one and come up with an error table on the less expensive units. The nonelectronic one may allow for some calibration (by brute force or otherwise). I would like to find sending units that would let me look at humidity levels inside and out at once -- cheaply! The Davis weather stations are too much $$$. Anyone else done the "wet bulb" thermometer science experiment? Evaporation of water delivered by a shoelace wick cools the thermometer bulb, more when it is drier, allowing calc of RH (no, I don't remember how -- maybe the wet bulb temp is roughly the dew point?). I think this is basically what a psychrometer does.
*yeah, it works on the wet bulb theory. I didn't want to throw in a totally geeky word like "psychrometer", but apparently Andrew has no shame.These can be calibrated, but they are only so accurate as i remember. Recording hygrothermographs are hooked up to a human hair, and are much more accurate than a psychrometer, and can be calibrated.On the small, cigar humidor units: save your money, unless you are looking for a ballpark. 5% is way optimistic in cheap units. This is just accepted among humidor makers. There are pretty, but unreliable cheap units; black plastic unreliable digital ones, and then you step up to ones that work for about 3K. Or you can go for the cabinet size units, monitered by modem 24 hours around the clock by technicians in Switzerland (no, I'm not kidding). The small ones can't be calibrated, and in my empirical experience of comparing, side by side, multiple units from different manufacturers, the amount they deviate is not consistent from day to day.
*I don't know a thing about humidity gauges. But, Andrew, I logged on to Grainger's about 6-8 weeks ago and requested a catalog. It had a message about the big catalog being too expensive to distribute to just anyone, so they'd send me a 1000 page (or 1000 item, can't remember) sample catalog. A little later, I got the behemoth one in the mail, with my own little customer number, a CD based version, etc. I haven't ordered from it yet, though. I expect shortly to order one of the circuit tracers I was looking for before. I don't remember if it was you who suggested Ideal's version, but that model has been discontinued. Anyway, apparently, anyone can go to Graingers. Plus there was a mention in the package I received about where the nearest branch office is located, so I expect anyone could go in off the street to the branch stores.Sean
*It was about three years ago but I had to go to the local branch with letterhead in hand to place my first order.
*In the back of the behemoth, it does say "wholesale only" and so does the site. The branch i visited had a warning on the door too. I look ratty enough these days that no one questions I'm "in the business." (No offense to anyone i hope!)Their site is AWFUL, tedious and confusing. It took me TWO HOURS this morning to get a simple order through. Be sure to register AND sign in before filling out an order form because otherwise the site won't let you place the order online or even save it while you sign in (?). The search function is nice because often the type of thing you want shows up in lots of different product categories. But the best way to order is if you already know the part #.I only have a couple of suppliers here who resist doing retail of any sort. I'm not certain of the business theory here, except avoiding too many small orders or some odd notion of "prestige."
*Oh yeah, on hygrometers (the generic term; a psychrometer is a hygrometer than uses the wet bulb method -- yeah, I'm a word geek ... ) -- anyone heard of the iButton? It is a tiny data storage device encased in a stainless steel shell, containing a fair amount of static memory and able to communicate wirelessly -- touch it against a pad and the data is transferred to your PC. It costs about $10 or can be purchased embedded in a signet ring, attached to a key fob, etc. It will run Java applets that you download or write yourself. Pretty cool.Check out: <a href=http://www.ibutton.com/index.html>iButton, esp. the "1-wire devices."To the point, they have weather sensors for this system; the hygrometer/temp meter is unfortunately $199 (temp alone is like $20). For the same price there's also a standalone datalogger that I can imagine using to monitor basement or attic or HVAC duct conditions in a client's house. Try: <a href=http://www.texas-weather.com/onewire.html>Texas WeatherI'm thinking I could set up a wet-bulb/dry-bulb sensor with two temp probes and have the iButton process these data into RH.
*Oh yeah, re hygrometers (the generic term: a psychrometer is a wet bulb method hygrometer -- yeah, I'm a shameless word geek) -- anyone heard of the iButton? It is a tiny data storage device encased in a stainless steel shell, containing a fair amount of static memory and able to communicate wirelessly -- touch it against a pad and the data is transferred to your PC. It costs about $10 or can be purchased embedded in a signet ring, attached to a key fob, etc. It will run Java applets that you download or write yourself. Pretty cool.Check out: <a href=http://www.ibutton.com/index.html>iButton, esp. the "1-wire devices."On point, they have weather sensors for this system. The hygrometer/temp meter is unfortunately $199 (temp alone is like $20). For the same price there's also a more interesting standalone datalogger that I can imagine using to monitor basement or attic or HVAC duct conditions in a client's house. Try: <a href=http://www.texas-weather.com/onewire.html>Texas WeatherI'm thinking I could set up a wet-bulb/dry-bulb sensor with two temp probes and have the iButton process these data into temp, dewpoint, % RH. If I had free time. :(
*Alan:A year or so ago Don Fugler of Canada Mortgage and Housing Corporation did a study of hygrometer precision. He found that the $30-$40 units (Radio Shack for example) were within +/- 5%RH provided they were not subjected to extreme dryness or wetness, and the environment was somewhat clean. It's best to ask to see a bunch of them at the store and take one that is reading in the mid-range, in order to not buy an outlier. The instrument will drift after a year or two. For homeowners, Fugler concluded, a $30 instrument is a good buy.Sling psychrometers generally give readings that are erroneously high, because the operator doesn't do enough slinging, and because of water impurities. Mechanically aspirated psychrometers with distilled water give good readings. But to convert the resulting wet bulb temperature to RH requires a precise (dry bulb) temperature reading. The error that results from these two instrument errors is probably still below the +-5%RH error in the cheaper instruments.Greater precision than +-5% costs more, and requires more frequent factory calibration. Vaisala makes instruments that many researchers consider the best, and they have a range from $hundreds to $thousands. The "gold standard" for humidity measurements uses a chilled mirror dew point sensor ($3000).Fugler report at:http://www.cmhc-schl.gc.ca/cmhc.html
*Thanks so much, BillR -I'm gathering from everybody's responses that there is a price to pay for accuracy. Too bad the technology/price haven't advanced at the same rate as consumer electronics.Seems to me there needs to be increased demand from the public or maybe I'm just one of very few humidity geeks out there.It is also interesting to hear the gauges lose their given accuracy after a certain period.I may pick up a couple more cheapo ones and compare to the ones I've been using for several years.Thanks again to all who responded.
*Alan and all fyi,I found a 1% accuracy rH psychrometer listed at Edmund Scientificfor about $180.00. http://www.edmundscientific.com/Products/Search.cfm?query=f36%2C881Hope this helpsMike
*my Bacharach sling-psychrometer is about 20 years old and the same model is still available from grainger for about $65...this model has mecury wet/dry bulbs....i use bottled water instead of distilled.. u can drink what u don't use... hah, hah
*Ok, Andrew and Ryan. I took a closer look, and you're right. But, how tough could it really be? I mean, if all they want is identification like letterhead, I can (ahem, theoretically) generate some nice stuff on a PC. I mean, unless they were to start demanding legal documents (some proof of a state registration, tax numbers, etc.) what would keep me? I can look as ratty as the next guy...Besides, I agree with Andrew. What's the point in not selling retail? The catalog proclaims they gladly accept orders as small as 'just a pack of AAA batteries.' The only valid reason would be some obscure obligation to their vendors that they are not selling retail. Naturally, this is all conjecture. I wouldn't conspire to defraud a company. ;)Sean
*I was a weather observer in the Air Force and we used a sling psychrometer. It was a metal plate chained to a handle. It had two calibrated thermometers - one with a cloth-bag wick on the bulb. You wet the wick and swing it for 30 seconds or so. When you stop you take a reading from the wet-bulb thermometer and then the dry-bulb. Those reading would then be set on a plastic "idiot" wheel and we would get the dew point and RH.Check one of those Scientific American/surplus stores for one.I wonder why they never came up with a good, cheap RH gage?
*Mike S - Thanks !!First time I saw the level of accuracy mentioned for a humidity gauge.
*Mike. I too have a 20 + year olkd Bacharach sling psychrometer. but I lost the instructions. How long must you whirl the thermometers? Because we distill our water we use distilled water to wet the wick. GeneL.
*gene... i usually sling about two minutes and i repeat until the results repeat..billr above (post #7) didn't say how long and i don't remember if the instructions ever did say how longwetting your wick is very important....
*Geez, this place is crawling with nerdz....And Mike with his dirty mind. :)