How to adjust my weather station?

February 20, 2015 8:49 AM

I need a help adjusting an analog weather station.

Ages ago, I was given one of those wall-mounted decorative analog weather stations, like this one (but not exactly. Mines in a big square frame. But the contents are the same).

Somewhere along the line, I lost the instructions on how to re-calibrate the hygrometer. I believe it entails placing a damp rag over an opening in the back and letting it sit there for a certain amount of time. I believe the idea is that this should peg the needle at 100%. If it doesn't, then you adjust the needle. I know...it's not terribly accurate. But, it's good enough for a decorative toy.

So, questions...
• How damp should the rag be? Soaked? Merely damp?
• How long should the rag sit over the opening?
• Or does the station sit on top of the rag?

My Google-Fu has really failed me on this one. I cannot find any instructions for this anywhere.
Any help will be greatly appreciated.

Thanks!

posted by Thorzdad to Science & Nature (4 answers total)

I would just bring it into a closed bathroom and take a hot shower. By the time you're finished, it should be reading 100% as long as you don't have a strong ventilation system operating. Alternatively, if you live someplace where it gets foggy, take it outside for 15 minutes while it is foggy and that should be 100%. As you say, cheap analog hygrometers are not very accurate anyway. I think either of those methods would probably be more effective than a wet cloth.
posted by jkent at 10:26 AM on February 20, 2015 [1 favorite]

Soaked but not dripping. I presume your hygrometer is doing the usual wet thermometer/dry thermometer trick, so it should have a wet surface touching it, but the surface in question should not be touching free water.
posted by Sunburnt at 10:44 AM on February 20, 2015

Sunburnt is describing a psychrometer, but I believe Thorzdad is referring to an inexpensive dial hygrometer. Those are usually either the metal-paper coil type or the hair tension type. With those types, there is no thermometer involved in the humidity measurement, even if the unit also includes a thermometer.
posted by jkent at 11:09 AM on February 20, 2015

Response by poster: ...I believe Thorzdad is referring to an inexpensive dial hygrometer
Yes. That's it exactly.
posted by Thorzdad at 1:29 PM on February 20, 2015