A digital hygrometer is a battery-operated instrument that measures the amount of humidity in the atmosphere from 0 to 100%. It works by calculating pressure and temperature changes. Digital hygrometers are often used in greenhouses, industrial premises, and outdoor spaces. They are equipped with sensors to measure fluctuations of moisture levels. These instruments have an accuracy level of +/-2%.
Does a digital hygrometer need to be calibrated? A digital hygrometer doesn’t need to be calibrated because it’s already calibrated in the factory. Because of its delicate design, you should test it before use.
Also, you should wait for 2-3 hours to allow the instrument to adapt to changes in humidity. Most of them are equipped with sensors which make them easy to read.
If the humidity levels are off, write down the percentage and subtract from regular settings. Unlike analog hygrometers, these units are equipped with built-in thermometers.
If the instrument is customizable, you’ll find a screw on the rear. But if there is no slot for calibration, follow the instructions on the manual. Make sure you calibrate your digital hygrometer if it gives a faulty reading of relative humidity.
How to calibrate a digital hygrometer
There are many methods of calibration, so you should choose the one that suits you best.
The salt solution method
Put some salt in a bottle cap and dampen with a few drops of water (don’t dissolve).
Place the cap and hygrometer in a see-through container. Leave it for a couple of hours and note the reading without opening the container.
The hygrometer should read 75%. If it reads 72%, this means that every time you measure humidity you should add 3 percentage points. Likewise, if it reads 80% the gauge is 5 percent high.
Depending on the type of salt used, you can get different humidity values. At 59 F, a solution consisting of lithium chloride gives a value of 12%, sodium chloride 76%, and magnesium chloride 86%. If you find the results above the expected reading, its time you calibrate your hygrometer.
Small glass method
Add table salt to a small glass and fill in with 5ml of water.
Place it inside a plastic bag together with the hygrometer and seal it. A word of caution – the salt solution should not touch the hygrometer. Make sure it sits on a flat surface to prevent spilling.
Don’t place the plastic bag near heating vents or direct sunlight. Leave it for 12 hours and check whether it will reach 75% or 76% mark.
The only drawback of this method is that the temperature is irrelevant. Nevertheless, 60 of humidity is achieved at 75%. At 59, 76% of humidity is achieved.
Based on the humidity standards, you should wait for a few hours before using the hygrometer. Although it’s a simple method, you should ensure there’s sufficient airflow. You’ll also get fault reading if you place it in the wrong position.
Damp cloth method
This calibration method involves wrapping a wet towel around the hygrometer. Leave it for 2-3 hours and unwrap the towel. It should read 98%. If the hygrometer shows a different reading, you should adjust it.
The only drawback with this approach is that the instrument does not measure with the same precision from 0-100% humidity. This method is simple and more practical. If the hygrometer reads 100% relative moisture (RH), then it’s 2% off.
The steam method
Pour three cups of saline solution in a pot. For every 100ml, add 40g of table salt. Once the salt is fully dissolved, place the hygrometer in a glass and insert it in the solution.
Make sure the lid has a tight air seal. Leave the pot for a few hours until you reach the ambient temperature. To get the humidity value of 70% and above, you should maintain an ambient temperature of 20 C.
After 2-3 hours, the instrument will read 74%. If there’s a deviation of 3 or 5 percentage points, proceed with calibration.
Adjusting a digital hygrometer after calibration
To locate the calibration button, check the user’s manual. If you want to adjust the humidity reading, turn the adjustment wheel counterclockwise. To lower the reading, turn the wheel in a clockwise direction.
After that, press the set button and lock the adjustment. Double-check to ensure, it reads correctly.
What to do if your digital hygrometer has no calibration button
Simply press the reset button and wait for the reading to reach a 75% mark. There’s another workaround for this. You can subtract the difference from the actual reading.
For example, if the reading is 80% you should subtract 5 from the actual reading. If you’re likely to forget the reading, make a notation on a masking tape. But before you measure the humidity levels, wait for 1-2 hours before you use the device.
Uses and applications of a calibrated digital hygrometer
You can use a hygrometer at home to balance humidity levels. When you maintain the level between 30 to 50%, you reduce the growth of mold and mildew.
This instrument eliminates the guesswork out of the equation. You can be sure the instrument will be helpful to allergic patients as both low and high humidity can aggravate the condition. A hygrometer will determine whether you should turn on your humidifier or a dehumidifier.
If you have a greenhouse around your house, a digital hygrometer can be used to measure the moisture levels. Still, some food items and beverages require a certain level of humidity.
A digital hygrometer can also be used in industrial spaces, incubators, and office buildings where humidity is a matter of concern. The sensors help in data logging, mapping, and creating data reports.
The most sophisticated hygrometers can be calibrated which means they display reliable values. Once in a while, a digital hygrometer can read lower than the percentage relative humidity.
Before you hurl it in the trash can, try to calibrate it. You must give the hygrometer 1-2 hours before taking the reading. When properly calibrated, a digital hygrometer has an error of +/-2%.
Final words
Whether you want your home to have an adequate level of humidity or get accurate readings for your warehouse, you need a hygrometer that gives accurate readings.
While this may sound complicated and confusing, you must ensure that your instrument is well-calibrated. A digital hygrometer should be tested once a year and adjusted accordingly.
This is because the sensor can drift anytime. If there’s no way for calibration, add or subtract the actual reading to get accurate humidity levels. Digital hygrometers are reliable than their analog counterparts. Don’t risk your health and personal items by relying on a faulty instrument.
