I need to do some environmental testing, including for humidity, inside a small temperature chamber. Humidity sensors are a dime a dozen, but how do you add humidity?
I see the ultrasonic mist humidifiers used to diffuse essential oils and the vaporizers which emit steam I'm thinking of using the steamer so it will operate during sub-freezing testing.
I'd consider something simple first; maybe just a bit of blotter paper next to a fan? It oughtn't be hard to measure water to achieve target humidity, assuming you start with dry air.
You should refer to the standard you're trying to meet, to get some numbers to aim at and even possibly some methods outlined.
A simple 20-30degC soak at 91-95% RH can be achieved rather simply by including a flattish container of a saturated potassium nitrate solution (saltpeter) inside the sealed test chamber. The solution acts as a simple regulator, so long as both water and visible crystals coexist in the tray.
This has long been an accepted preconditioning method for safety insulation testing.
Humidity testing below freezing isn't humidity testing, it's making snow cones.
RL
To achive 75% Rh regular salt can be used.
Marcin
Both those ways are what I use to cal my humidity meters.
A pan of water with a heater in it?
*** humidty rant*** Humidity is a strong function of temperature, to me, it's a silly weather unit. I'd much rather know the dew point, which (AFAIK) doesn't change with T. *** end rant***George H.
Yep. A direct expression of water content. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
Hillary criticizes Trump's business acumen... air tight contracts where he can't lose money on the deal.
Yet Hillary (aka Judas Chappaqua) sells the US itself down the river simply for contributions to the Clinton "Foundation".
Pastes of salts of different metals will saturate the air to different, specific humiditys. Here's a nice table:
I need to do some environmental testing, including for humidity, inside a small temperature chamber. Humidity sensors are a dime a dozen, but how do you add humidity?
I see the ultrasonic mist humidifiers used to diffuse essential oils and the vaporizers which emit steam I'm thinking of using the steamer so it will operate during sub-freezing testing. ================================================================
It is very difficult to do a good humidification system that has to work over a large temperature range, especially when that range goes much below room temperature. What temperature range do you need to cover, if you have active cooling in your chamber how does it work, how much colder does it get relative to the chamber at the coldest temperature you need to maintain (you have a lovely opportunity to make a still here that dumps your water supply into the bottom of your chamber as fast as you can inject it, speaking from experience :-)), what relative humidity range do you need to cover, and do you have active air circulation in the chamber? I've developed humidification options for shaker incubator cabinets so if you give some target specs I can probably help.
----- Regards, Carl Ijames
Lay off the salts and oils as they both make a mess of whatever you're testing. High humidity salt (spray) is quite conductive and will make almost any PCB that isn't conformal coated fail.
We had that problem when testing marine radios. The big problem was getting non-condensing humidity. Raising the humidity was easy enough. We would use an ultrasonic nebulizer (conveniently manufactured by another division of the same company) to vaporize deionized water. There was a dew point (condensation) detector borrowed from some weather station to detect when the nebulizer had pumped too much water into the air. There was also a circulation fan to insure that the humidity was even. Water vapor tends to accumulate near the bottom of the chamber.
At the low end, we use a refrigerated compressed air dryer commonly found in machine shops and places where one really doesn't want to pump compressed air and water into pneumatics. For example: If you're not going to do this on a regular basis or don't want to blow your budget on the cooling unit, you can absorb moisture with a desiccant: I don't recall the numbers but I was never able to get desiccated air down low enough in humidity and had to use the fridge. Note that at very low humidity levels, strange things start to happen with electrostatic discharges and charge accumulations. No lightning bolts but plenty of destroyed electronics.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I beg to differ: Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation.
The dew point is the temperature below which water vapor condenses. In other words, the dew point is measured in units of temperature and is therefore not a function of temperature.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I controlled gas mixture with valving. Seems like you could add near saturated air with pump and valve.
Greg
You misconscrewed George's statement... he spoke of "humidity" (as in percent) touted by your typical TV "weatherman". That form of "humidity" _is_ a function of temperature... because it's percent of water vapor capacity of air at a specific temperature. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Hillary criticizes Trump's business acumen... air tight contracts where he can't lose money on the deal. Yet Hillary (aka Judas Chappaqua) sells the US itself down the river simply for contributions to the Clinton "Foundation".
Naw, I never make mistakes. I was referring to the 2nd sentence: "I'd much rather know the dew point, which (AFAIK) doesn't change with T." which makes no sense. When one refers to dew point, it is specified as the "dew point temperature" and therefore cannot be a function of temperature.
Incidentally, if you want to see dew point in action, wait until we have a nice cold morning, which caused condensation to form on the automobile windshield. The usual method of removing the water is to turn on the defroster and blow hot air onto the inside of the windshield, which eventually evaporates the moisture. However, turning on the air conditioner works better, because cold air is fairly "dry" because it holds less moisture than warm air. Turning on the air conditioner on a cold morning is rather non-intuitive, but it works. Actually, it's not quite that simple: (6:28)
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
What's condensation ?>:-}
I've known of the A/C trick since perhaps ~1964, when I had to drive back to WV for my sister's wedding.
WV and MA are why I live in AZ ;-) ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Hillary criticizes Trump's business acumen... air tight contracts where he can't lose money on the deal. Yet Hillary (aka Judas Chappaqua) sells the US itself down the river simply for contributions to the Clinton "Foundation".
Varying the dew point is easy. Varying the RH is harder, because the H2O saturation point is such a strong function of temperature.
To the OP: Do you need something other than 85/85 for humidity? That's the usual torture test, ISTR. You can get that with a tea kettle and a vacuum cleaner hose. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
It's not that simple; compression can cause condensation, adiabatic expansion can cause condensation. Your pump will alter your air.
It does make sense. What he's saying is that the dewpoint doesn't change (much) over a range of the *current* temperature. As a day progresses and it gets hotter, the relative humidity normally goes down, but the dewpoint (or absolute humidity) doesn't. Of course, as it gets hotter more water evaporates so the absolute humidity will change.
Sorry. I forgot that you live in an area known for dry climate, dry humor, and low humility. Condensation, as in an air conditioning condenser, is part of what makes your desert habitable. I'm told that the temperature scale in AZ is hot, hotter, and unbearable. Rumor has it that residents live in caves or underground facilities in the manner of troglodytes, but since I haven't been there, I can't confirm this rumor.
I discovered it in about 2005, when I finally bought a car that came with an air conditioner. My previous vehicles either lacked air conditioning, or had one that didn't work.
The climate in AZ is why I live in paradise and near the ocean. We occasionally have this phenomenon called "rain", where the atmospheric temperature drops below the dew point, causing water to condense out of the air. That makes the 200+ ft cellulose monopoles grow, which provide shade and transpiration cooling, so that the area does not turn into AZ.
I was given a window mounted air conditioner as a present, but gave it back. I didn't need it, didn't want to pay the electric bill, didn't want the noise, and couldn't find a place to install it. So, I gave it back.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Dry wry ;-)
It _is_ hotter than hell here, and people are advised to stay away, for their presence increases the temperature.
I would be perfectly happy in a cave... my wife resists.
I understand we will have our annual rain within the next few weeks... visitors are advised to stay away. If they arrive they will first be turned into pillars of salt, then dissolved by the rain >:-}
Our central air is quiet... and our electric rates are far lower per kWh than in "paradise"; plus we don't dump fresh water into the ocean to protect some non-essential called the "snail darter" ;-) ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Hillary criticizes Trump's business acumen... air tight contracts where he can't lose money on the deal. Yet Hillary (aka Judas Chappaqua) sells the US itself down the river simply for contributions to the Clinton "Foundation".
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