Calibrate a Hygrometer

Hydroman52
Posts: 0
Joined: Sat Apr 11, 2009 7:52 am
Status: Offline

Sun Jul 18, 2010 11:36 am

One item that is in each of my guitar cases is a digital hygrometer/thermometer to monitor humidity and temperature. I always wonder about their accuracy and have contemplated getting a calibration kit to test them all. While shopping for another hygrometer for a new addition, I came across this simple method (and it’s cheap just like me) to check them. I plan on trying this when I get done with my heavy summer work schedule and before the winter dry season.

How to Test and Calibrate a Hygrometer
1. Fill a milk bottle cap, soda bottle cap, beer bottle cap, or other small container with salt, and add a few drops of water (not enough to dissolve the salt – just enough to get it wet). You don't want a salt water solution, just damp salt.

2. Put the cap inside of a zip-lock baggie along with your hygrometer and seal the baggie with some air trapped inside (so it is not tight against the hygrometer) and let it sit.

3. Wait 6 hours for it to stabilize, then check the reading on your hygrometer without opening the bag (or immediately after removing). If the reading is 75%, then your hygrometer is accurate and no adjustment is required.

4. If the reading is not precisely 75%, then adjust the hygrometer to 75% (usually by turning a screw or dial, or pressing a calibration button). This must be done immediately after removing from the bag, before room conditions cause the reading to change. With some hygrometers, you may be able to calibrate without removing from the bag. This is the best way to do it.

If there is no screw, dial, or button to recalibrate your hygrometer, then you will just have to remember to add or subtract the difference between the test reading and 75%, in order to determine the actual humidity level. For example, if your hygrometer test reading was 80%, then subtract 5% from the readings you get to determine the actual levels of humidity (e.g. a reading of 70% equals an actual humidity level of 65%).

Hygrometers should be tested at least once a year, and re-calibrated if necessary.

I use Caliber III Thermometer/Hygrometers by Western Humidor which have a Hi/Lo memory feature, but have no ability to be calibrated. Therefore, I will put a label on each one showing how much to add or subtract once I figure out the accuracy.


Hope this helps,
Hydroman52