I've used several different types of humidity sensors (all digital) and pretty much took them for granted. That was until my last sensor (an Acurite 613
)crapped out in the cave. This was the second sensor that I had to die on me so I thought I'd do some investigating. I opened up the Acurite and found the sensor (the white chip in the middle of the picture below). Thought it may have gotten coated with whatever was floating around in the cave and gave it a light alcohol wipe. It only made the reading more off
so I replaced the whole unit with a new Acurite I had on hand. Came across this excellent article
and from the pictures recognized that what the Acurite sensor was a resistive sensor (as opposed to capacitive or thermal conducting per the article). I also found that resistive sensors rely on a coating material of a conductive salt or polymer which explains that the alcohol wipe is probably the worst thing to do. That said, I'm not sure any of the three digital technologies would be completely free from failing because of the conditions in a cave fridge. I guess you can resort to analog (poor accuracy) or a wet-bulb / dry-bulb (and run the RH calculations), but when they work the digitals are inexpensive and good accuracy.
The article says one good thing about the resistive sensor is that it is field replaceable so I ordered 10 from Ebay
. I really like the Acurite and have several so I figured it would be worth $8 to have a lifetime supply (if they work!). I know some of you on the forum have this same model based on your cave pictures, so if you experience sensor failure I would be happy to drop one of the chips in the mail to you.
If I do order a new sensor I'm going to get one with a remote sensor. Found this one
that looked interesting; sensor wire is only 18" but it does have dew point display. Curious if anyone out their has a sensor or method they think is the "best".