Welcome to our forum. A Message To Our New and Prospective Members . Check out our Forum Rules. Lets keep this forum an enjoyable place to visit.

Please consider registering
sp_LogInOut Log Insp_Registration Register
Register | Lost password?
Advanced Search
Forum Scope


Forum Options

Minimum search word length is 3 characters - maximum search word length is 84 characters
sp_Feed Topic RSSsp_TopicIcon
What do you do when half your humidistats lie to you?
Topic Rating: 0 Topic Rating: 0 Topic Rating: 0 Topic Rating: 0 Topic Rating: 0 Topic Rating: 0 (0 votes) 

February 17, 2017 - 5:54 pm
Member Since: June 7, 2016
Forum Posts: 373
sp_UserOfflineSmall Offline

There's an old saying that a man who has a clock always knows what time it is, but a man who has more than one is never really sure.

I ran into the humidistat version of that today. I used to not care what the humidity was in the house. It would occasionally get so dry that I'd need Chapstick or something similar, but otherwise I didn't really worry about it.

Getting a quality violin changed that. So I bought a whole-house humidifier, and finally got it set up today. Pierre (Fiddlerman) had recommended a digital humidistat a week or so ago, so I got one of those, too.

The digital one said it was 35-37% - rather low.  When I turned on the humidifier for the first time, it said 47%. I moved it some (the first place I measured was towards the back of the house, the humidifier is more towards the front, and it went up to 52%. The digital one said that same area was 41%.

So I dug out the two cases I have that have humidistats in them. One agreed with the humidifier, one agreed with the digital humidistat.

But I found a way out, which is why I'm posting. https://planetcalc.com/2167/ is a converter from absolute to relative humidity, and vice versa.

I got the temperature, (relative) humidity, and barometric pressure from weather.com. That gave me an absolute humidity. Then I used that number to calculate the relative humidity at the (somewhat warmer) temperature inside the house.  Within a couple of percent, it agreed with the digital humidistat, so that's probably what I'll trust now.

Just in case anyone found that explanation confusing, I put in:

51% relative humidity (from weather.com)

20 degrees Centigrade for air temperature (also from weather.com. If you get your weather in degrees F, you'll have translate.  Search google for 'degrees f to c'.)

1007.8 mm Hg for barometric pressure (also from weather.com)

Calculation precision 3  (the default, and probably as high as was justified.)


That gave me .009


I then went down to the section below it (absolute to relative) and put in

Absolute humidity    0.009

Air temperature       24    (inside my house)

Barometric pressure  1007.8  mm Hg (same as above, unless you have the Big Bad Wolf trying to blow your house down.)

That gave me 41% relative humidity, which matched the digital humidistat.


Hope this helps somebody.


February 17, 2017 - 6:06 pm
Member Since: June 7, 2016
Forum Posts: 373
sp_UserOfflineSmall Offline

Update: You can pretty much ignore the air pressure. I finally got it to react, but I had to use insane numbers (like 15,000 mm Hg, 15 times normal atmospheric pressure) to get it to react.   If you're planning to keep your violin in a pressurized scuba tank, you may need to take this into consideration.  For everybody else, anything halfway near 1000 will give you sane results.

Fort Lauderdale
February 23, 2017 - 10:23 am
Member Since: September 26, 2010
Forum Posts: 16074

Thanks for all your research and information.

"The richest person is not the one who has the most,
but the one who needs the least."

Forum Timezone: America/New_York
Most Users Ever Online: 696
Currently Online: JohnG, Thomas B.
Guest(s) 59
Currently Browsing this Page:
1 Guest(s)
Members Birthdays
Today None
Upcoming Killerkhezu, Ferret, HDuaneaz, vibaviattigala, BillyG, rsmith6322, zpilot, Rafael Gonzales, ACDSherlockian, NiloiV, jose6ph, Kody, music_master
Top Posters:
ELCBK: 5033
Mad_Wed: 2849
Barry: 2680
ABitRusty: 2678
Fiddlestix: 2647
Oliver: 2439
DanielB: 2379
Gordon Shumway: 2103
damfino: 2048
Kevin M.: 1973
Member Stats:
Guest Posters: 3
Members: 31104
Moderators: 0
Admins: 7
Forum Stats:
Groups: 16
Forums: 79
Topics: 9918
Posts: 124771
Newest Members:
Administrators: Fiddlerman: 16074, KindaScratchy: 1760, coolpinkone: 4180, BillyG: 3741, MrsFiddlerman: 2, Jimmie Bjorling: 0, Mouse: 4185