Just on impulse, I added a cheap hygrometer to an order I made recently on my tools and machines supply company. It’s one of those pretty little meters sold as “fit-ups” - thermometers, hygrometers, barometers to set into lumps of wood to sell at markets etc. I was interested to see how good or bad they were - could they be useful for fluteplayers wanting to maintain the humidity of their flutes within safe limits.
I was a bit surprised to see, when it arrived, it indicated about 70%. Hmmm, must be damp in Brisbane, I thought. Hours later and it’s still resolutely maintaining a reading of 70%, despite sitting next to my extremely expensive guaranteed-to-2%-accurate lab meter which reported just under 40%. Days later, they still maintained the standoff. Oh well, what can you expect in a cheap meter? It would be insisting all was well while flutes cracked around it!
With nothing to lose, I pried the back off to see if the thing was in any way adjustable, and sure enough, the end of the sensor coil is secured to a bent metal plate which can be rotated to adjust the reading. A little blob of soft glue had been added to lock the current setting. That flicked off with a scalpel, leaving the plate easy to move. I set it to read the same as the lab meter and they now seem to track well together.
So, moral of the story?
Don’t trust a cheap hygrometer - check it. That’s as easy as leaving it outside on the windowsill while you watch the weather report on the TV news. When they give the current humidity, check the meter.
Secondly, if it’s wrong, don’t just chuck it in the bin - pop the back off and see if it can be adjusted.
I had four ~$10 hygrometers that all read about the same. Then I bought three digital ones (which I thought had remote sensors to put in my tupperwares, but which dont). Lo and behold, just as Terry said, the four were all reading~55-60% while the good ones were reading ~40%. Two of the cheapies were adjustable, two not.
I keep meaning to bring some dessicant home to test them at 0%. I’ve tested them at 100%, and they’re accurate there. Another fixed point, and I should know whether they really do work as well as the company says.
I use one of the little digital ones that can record the day’s high and low temps and humidity – if one remembers to reset it. Cost about $28.
Do you ever use a moisture meter on your wood? I use something called a “Mini-Ligno”. I use it mostly to monitor the changes in humidity of my wood supply between dry times and wet times - as well as to test pieces that seem somewhat wet. Usually my wood stays around 8-9% minimum to 12-14% maximum, depending upon the season.
I know luthiers making stringed instruments want their wood drier (5%) for varnishing purposes but for wind instruments that are getting moisture saturated air blown into them, that degree of dryness seems risky. Curious what your thoughts are.
This is a simple and precise way to calibrate a hygrometer: take a small container like a bottle cap, and fill it with salt. Make the salt damp with water (don’t soak the salt completely). Place the wet salt and your hygrometer in a ziploc bag, and leave for 8 hours. Your hygrometer should read 75%.
I totally agree. I’ve been buying them in batches from a humidor supply company and include one in the case with each flute I ship out. When I get a box of 50 hygrometers there is often a variation in readings from 20% to 70%. I calibrate them against an Oregon Scientific digital hygrometer which reads accurately on the wet salt test that was mentioned by ro3b. We set up a little assembly line for the calibration, and I pay my kids 50 cents per unit for disassembly and re-assembly.
Man you guys are rich if’n ya can buy one.
I just make one and test it against my standard.
PS I would like to add that the wet bulb technique may be a cheap (and foolproof???) way to calibrate a hydrometer if a fan is used on the wet bulb like a Sling psychrometer.
