humidity and hygrometers

powderful

Member

• Apr 30, 2014

• #1

A few nights back I noticed my hygrometer was spiking into 90% humidity so naturally I panicked and bought some calcium chloride and hung it up. Sure enough it started dripping into the bucket pretty fast which would indicate above 50% humidity (according to the directions).

The CC worked to a very small degree and I managed to get it to peak around 80 but that is still too high considering I am just starting to flower the girls.

So I hop in the car and get a dehumidifier and while I was in the store I picked up a digital hygrometer as the one I had was analog and originally designed for saunas. Got home and the digital hygrometer reads 37% max pretty much wherever I set it in the tent but the dehumidifier has been going (set to 40%) non stop.

tldr; Dehumidifier set at 40% working non-stop,calcium chloride absorbing moisture, analog hygrometer showing 83% and digital hygrometer showing 37%.

My question is this:

Is there any way to test the hygrometers to ascertain which is the accurate reading?

 

tleaf jr.

Came up off 75w

Veteran

• Apr 30, 2014

• #2

only thing I could think of is to get a few hygrometers and set them all together and take a estimate from all the results .

 

T

The Meadows

Member

• Apr 30, 2014

• #3

Calibration Test Procedure
Mix common table salt with tap water until you have a completely saturated solution with no standing water.
Place about 1 inch of the saturated salt solution in an open container or bowl that is approximately 4 inches high. The 3 inches above the solution will contain air with a predictable humidity value. You can use a cut away container as shown in the figure below. One edge of the container is cut slightly lower to rest the sensor on the lip.
Place this container and the sensors in a waterproof zip lock plastic bag, as shown in the figure below. Leave one of the corners open and remove all of the remaining air with a straw. Close the air tight bag.
Leave the sensor in the bag for four days or 96 hours to completely stabilize.
The sensor should read 75% plus or minus the sensors rated margin of error. For example, if the sensor is rated at +/- 5%, the display should read between 70 and 80% relative humidity.
If the sensor is adjustable or calibrateable, set the humidity on the display to 75%.
Repeat this procedure once per year to account for electronic drift (sensor contamination).

 

T

The Meadows

Member

• Apr 30, 2014

• #4

The above was taken from:
http://ambientweather.wikispaces.com/Humidity+Calibration,+Saturated+Salt+Test

 

Hammerhead

Disabled Farmer

ICMag Donor

Veteran

• Apr 30, 2014

• #5

yes they have calibration kits from Bovida. I used 1 to cal the meter when I first got it. I have found a cheaper way to do it. Just get a 62% Bovida pack put that in a jar with your meter for 24hrs. if it doesn't read 62% you will know how far it's off. The new Caliber 4 have a set point that you can adjust to show the correct reading.

This is the cal kit
http://www.ebay.com/itm/141204374042?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

 

powderful

Member

• Apr 30, 2014

• #6

I found that method but don't have any salt (moved to new house), any other methods guys?

I'm gonna go get salt and zip locks tomorrow as it seems like the most accurate method.

Opinions on duration of the test? Some webpages say 8-12 and some 96 hours.

 

MIway

Registered User

Veteran

• Apr 30, 2014

• #7

^^ the caliber hygrometers recommend against the salt method... inaccurate + can build up on sensor... if i recall correctly. could use a boveda humidity pack instead.

 

Mikell

Dipshit Know-Nothing

ICMag Donor

Veteran

• Apr 30, 2014

• #8

Boveda uses salt...?

Super interesting, they make cannabis curing products. Ain't it nice to be mainstream now?

 

powderful

Member

• Apr 30, 2014

• #9

Boveda uses salt, is unavailable in the area that I live and ordering online is out of the question.

I find it so strange that the 3 sources of humidity indication I have are telling me different things

 

Hammerhead

Disabled Farmer

ICMag Donor

Veteran

• Apr 30, 2014

• #10

Yes but its all contained in a packet. It wont get on the meter. very convenient.. If ordering online is out then you have limited choices. The only way I know is to mix of a salt bath then you need a air tight container that large enough to fit the salt bath and your meter should read 75%.

This is how Boveda works
https://www.youtube.com/watch?v=d688Zx5M1Vk#t=57


Here is a u-tube on how to mix up a batch
https://www.youtube.com/watch?v=2X-PzSS-OdA

 

powderful

Member

• Apr 30, 2014

• #11

Thanks for the help guys

Going to try the salt method on the analog hygrometer first, hopefully this is the one giving me a false reading.

Also found out that some dehumidifiers run the fan constantly but turn off the compressor at the RH level set by the consumer.

 

T

The Meadows

Member

• Apr 30, 2014

• #12

Some sensors need to be "conditioned". The DHT11 sensor, for instance, says to put it at 110 degrees F and < 10% humidity for a few hours then put it at 70 degrees F and > 80% humidity for 24 hours.

For what its worth, I did that with a couple DHT11's and it didn't help. It seems humidity can be tricky to sense.

 

powderful

Member

• Apr 30, 2014

• #13

Checked through instructions and online for any mention of conditioning for my wilfa hy-1 digital hygrometer and didn't turn up anything.

Found this though:

Use the same Salt Test method using any of the following: Lithium Chloride, Magnesium Chloride, Potassium Carbonate, Potassium Sulfate. The readings for these should be 11%; 33%; 43%; and 97% respectively.

Don't have any of those handy and can't validate the information so I will try the salt calibration first.

It is good to see a forum filled with people who take the time to come with informed input and a good attitude

 

M

Moonshine17

New member

• Feb 4, 2017

• #14

Hello all. All this has me confused. Which isn't hard I guess. But, my genetics are cracked and bout ready to go to soil. I was going to put them straight into 5 gal finishing smart pots. Have 4x2x5 grow tent. It has to be outside on covered porch, but not enclosed. Because the huge swings in temp in my area, (ne fl ) the rh spiked as high as 94% in 55* temp. Slight condensation on inside panels of Mylar.

I was trying to figure this out asap as I only have about 15 hrs or so to do so. Can anyone offer advice. Thanks!!