Making a regulated humidity chamber

[cheese9988]

This forum seems the closest for this project. I am trying to build a humidity chamber to check various humidity/dew point devices. I was going to build a chamber with two layers of plexiglass. Between the layers I was going to pump in dry compressed air to lower the humidity and that would be allowed to blow into the area in the center. I have a standard that I monitor it with. The thing I need is the same humidity all over the chamber. Would this be the best way, pump it in through small holes in the walls to circulate and lower the humidity in the air? I was also thinking of putting a pan on the bottom covered by a screen that contains salt and water that would keep it normally around 75% rh in the chamber and then the compressed air would fight and lower the humidity. What do you guys think?

 

[MikeHalloran]

Anyone who's ever tried to work with it knows that there ain't no such thing as dry compressed air.

You can't just pump something into a closed chamber and maintain any kind of equilibrium without also taking some out.

;---

You can probably kluge up something with air flowing in a loop through a small dehumidifier and your test chamber. You may have to use a room- size chamber to get the control loop to stabilize.





Mike Halloran
Pembroke Pines, FL, USA

 

[cheese9988]

It will have some outlets on the top that I can use to put my standard through.

 

[m777182]

To check humidity sensors you do not need a very large chamber.I think that the idea of putting a pan on the bottom that contains salt and water, covered by a screen, is a good start. With different salts you can keep humidity in chamber in a range of about 10% to 95% r.h. A ventilator above the screen will keep the air moving. You can make it simple and cheap but still reliable.
The problem I see is that you will have some more work to find data for salts to cover the whole range of r.h.'s at different temperatures.Do not forget that the solutions of salts should be saturated.
m777182

 

[unclesyd]

There are hundreds of companies that make all sorts of environmental test chambers. Do a search on "environmental chambers".
There is also a large number on the surplus market.

We had several chambers from the following.

http://www.cszindustrial.com/products/tempchambers/zplus.htm

 

[cheese9988]

To make the 75% point I just need ordinary table salt and water. I need to make a chamber without the need for salts all the time, just need it somewhat stable and be able to go to maybe 10% rh. One salt point is ok but don't want to change it all the time. The room has strick climate control so the temperature won't be too much of an issue with the humidity. I have tried doing this in a container, with success, but it isn't as stable, I added salt water and it worked a little better. But its only a small bottle.