How to Set a Hygrometer

A hygrometer is a device that measures the relative humidity in the atmosphere. Because relative humidity is a function of temperature and absolute humidity, the hygrometer's reading will be affected by temperature variations in the test chamber. Also, a hygrometer must be calibrated in air, which does not transfer heat very efficiently. This combination of factors means that a hygrometer is subject to drift in its measurements and must be calibrated frequently.

Things You'll Need

• Table salt
• Bottle cap
• Water
• Hygrometer
• Plastic zipper bag

Instructions

1. Place a teaspoon of salt in the bottle cap and add water one drop at a time to make the salt damp but not wet. Place the hygrometer in the zipper bag along the bottle cap of salt.

2. Allow some air into the bag and seal it. Allow the bag to sit undisturbed for at least six hours. Read the hygrometer without opening the bag. A correctly calibrated hygrometer should have a reading of 75 percent.

3. Record the correction factor of your hygrometer by subtracting the hygrometer reading from 75 percent. Your next step will depend on whether or not your hygrometer is adjustable.

4. Add the correction factor to your hygrometer's reading if your hygrometer is not adjustable. Be sure to apply the correct sign of your correction factor.

5. Adjust the hygrometer by the appropriate correction factor if your hygrometer is adjustable. These types of hygrometers will typically have a dial in the back which will change the reading.

References

• Cheaphumidors.com