Expert: James Yee - 3/3/2010

Question
how do u do a salt test so u can calibarate a new digital hygrometer.... thanks...

Answer
Hi JR,

First, some digital hygrometers do not require calibration.  Most digital hygrometers are factory calibrated and extremely accurate straight out of the box.  You should check your hygrometer's instruction manual to see if it needs calibration.

To salt test your hygrometer, you will need the following:

1 Small dish or bowl (a small cup or bottle cap will even work)
1 Teaspoon of regular salt
1 Ziploc bag or tupperware container with lid
1 tiny amount of distilled water
1 your hygrometer

First, take the teaspoon of salt and pour it into the small dish, cup or bottlecap.  Next, add a few small drops of distilled water and stir it up.  The water-salt mixture should be "crumbly" and not like a paste.  If it is too pasty/runny, add a tiny bit more salt to make it crumbly.  Next, place the small dish with the mixture inside the Ziploc bag or tupperware container.  Place your hygrometer inside the bag.  The hygrometer can be placed anywhere inside the bag/container but DO NOT let the hygrometer touch the salt mixture.  (If any of the salt mixture spills or comes in contact with the hygrometer, it can damage the sensitive internal mechanisms.

Next, seal up the ziploc bag (or cover the tupperware container with the lid... it does not need to be sealed airtight.) and let it sit for 6-8 hours.  After 6-8 hours, the hygrometer should display a humidity level of 75% humidity.  If the humidity level reads 75%, your hygrometer is already accurate and does not need to be calibrated.  If the humidity level does not read 75%, adjust the reading so that it reads 75%.  (For example, if the hygrometer displays a reading of 78% after 6-8 hours, it means that the calibration is off by 3% so adjust it accordingly.

For analog hygrometers, the calibration pin is usually located on the back of the unit and is usually a knob or screw that you need to turn.  For digital hygrometers (if calibration is available), you will need to check the instruction manual to see which buttons you need to press to adjust the displayed reading (it varies by manufacturer and hygrometer model).

Hopes this helps.  If you have any more questions, please feel free to just ask and I will be happy to help.

Regards,
James