A guide to calibrating a digital hygrometer using the salt test method
It’s always a good idea to check the accuracy of your hygrometer. You can use the Salt Test method on both digital and analog hygrometers. Most hygrometers today can either be adjusted or calibrated to an accurate reading. The salt test method won’t fail you, and it’s very easy to do.
- Small sandwich ziplock baggy
- Bottle cap from 2 liter soda bottle (works best)
- Table salt
- Hygrometer (whichever one you want to test, digital or analog)
Now that you have all of your materials handy, follow these steps and you’ll be on your way to effectively checking the accuracy of your hygrometer.
Fill bottle cap with standard table salt; fill about 3/4 of the way up.
Add tap water to the bottle cap to saturate the salt. If you see water floating on top of the salt, you’ve added too much water. Easy fix for this is to grab a paper towel, and soak up all of the excess water. You want more of a slurry consistency of water and salt. Again, if you see water actually floating on top of the salt, soak up the excess with a paper towel.
Place both hygrometer and bottle cap (with salt/water mixture) inside of a small ziplock baggy, as pictured above. Wait 4 hours and come back for a reading check.
If your hygrometer is perfectly accurate, it will read 75%. Most hygrometers will be +/- 3 %. If your hygrometer is digital and has a calibration button, follow the directions that it came with to calibrate to 75%. Digital hygrometers have a calibration button you push, while analog hygrometers have a screw which allows you to adjust the needle accordingly.
If your hygrometer is not adjustable, you’ll just have to make a note and remember how far off it is.
That’s all there is to it!
You’ve just calibrated/tested your hygrometer using the famous Salt Test Method.
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