What causes Hydrometers to Un-Calibrate?

[Flynnster]

Hey everyone, got my first humidor set up about 6 months ago and things had been going great. It's got a Heartfelt bead tube in it and the humidity always stayed around 65%. Over the last month of so I noticed the humidity ramping up and it finally got too high so I took out all my cigars, sealed everything with sealant, and am now re-seasoning.

I've got the hydrometer in a bag doing the salt test right now and it is reading 88%, way high. I tested it when I first set it up and calibrated it properly.

What causes them to become un-calibrated?

[Porch Dweller]

I've noticed that mine stay accurate for around six months or so, then need the battery changed. So every six months I change the battery and re-calibrate them.

[RWhisenand]

If you have an electronic hygrometer it works by reading the electrical resistance across a medium such as lithium chloride. As the batteries begin to degrade, the slight decrease in voltage will effect the resistance across the lithium chloride causing a false reading. By switching to lithium ion batteries you will reduce this need for calibration but not eliminate it altogether.


How this helped, BtW I spent 17 years in the field as an instrumentation tech, prior to moving into systems integration, and now management. I dig this stuff.

[markem]

Here is an interesting article about why thermometers and hydrometers need to be recalibrated. I would think that hygrometers would be similar. Stress on the medium over time plus fluctuations in the environment make a difference for small sensors.

http://www.icllabs.com/whyrecalibrate.html

[8zeros]

I blame entropy. I use it as an excuse for a lot of things.
"Why is this garage such a mess?"
"Entropy!"

[RWhisenand]

Originally Posted by 8zeros

I blame entropy. I use it as an excuse for a lot of things.
"Why is this garage such a mess?"
"Entropy!"

Entropy, it's not what it used to be.

[shilala]

Originally Posted by RWhisenand

Entropy, it's not what it used to be.

Nerd joke!!!

I should add that I use "my hygrometer says something stupid" as battery changing time. Much like the smoke detector beeping.
Rob explained it perfectly. I can add a little nugget to that...
The Hygroset II's that most of us use have sticky crap on the board that reads the RH. Get a bead stuck on there and it'll read any kind of bizarro stuff it wants to. I regularly look in the grill and see if anything is stuck to the board. Most guys probably won't have that problem, but it happens. To me, it happens a lot.

[Flynnster]

Awesome, thanks for all the advice guys. Looks like I'll let it finish re-seasoning, then put the sticks back in with the beads and a new battery.

[Chimneyfish]

Originally Posted by 8zeros

I blame entropy. I use it as an excuse for a lot of things.
"Why is this garage such a mess?"
"Entropy!"

yupp. right there. in conjunction with that lithium guy should explain everything you need to know there