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How To Properly Calibrate A Hygrometer: Best Methods For Accurate Readings

It is always a good idea to know how accurate your hygrometer is. If you calibrate it correctly, you will get the most accurate readings possible and adequately maintain humidity levels in your home or office. In this article, we discuss everything you need to know about calibration and offer tips for success.
How To Properly Calibrate A Hygrometer: Best Methods For Accurate Readings

How often do you check the humidity in your home? If it’s not a very high priority, read this article to find out why it is a mistake. 

Besides being uncomfortable and sweaty, too much or too little humidity can lead to expensive problems like mold and other structural damages. But don’t worry! There are many easy ways to get accurate readings on your hygrometer, so you know when there’s an issue.

Why do you need to calibrate a hygrometer? 

The hygrometer is a device used to determine the amount of moisture in a given space. The readings are used in numerous scenarios to detect the level of humidity, determine if there’s any mold or mildew growth, what products best suit your needs, etc.

Calibration is necessary to ensure that the hygrometer gives accurate measurements and helps you take appropriate actions when needed. 

In addition to this, calibrating the device will help you determine whether it’s time to replace it or any repairs needed

Sometimes hygrometers may be slightly off and indicate high humidity levels when they’re fine because of sensor malfunctioning. If that is the case, you can recalibrate the device and use it for longer until its next checkup.

Calibration is also required if you want to compare hygrometer readings with those of another person or company and when tracking trends over time.

Usually, one calibration would be enough, but in some cases where humidity levels fluctuate, and the device is used often, it’s advised to recalibrate every few months. 

How to Calibrate a Digital Hygrometer

How to Calibrate a Digital Hygrometer

The best method to calibrate the digital hygrometer is with salt or pellets (calcium chloride) because they are accurate and easy to calibrate.

Calibrating your device in this manner ensures you get an accurate reading when measuring the relative humidity in conditions that don’t require a high degree of accuracy.

  • You need to place the salt tablet or pellets inside a sealable plastic baggie. You must make sure that your device is in the open air before putting it in the baggie to ensure an accurate reading.
  • Close up the bag and wait until both samples reach equilibrium (until they are at precisely the same conditions). This will take about 10 minutes.
  • Now read your humidity meter and write it.
  • Take out the hygrometer from its plastic baggie, and wipe it clean with a cloth or paper towel before using it again.

📌 You must also wait for about 15 minutes after calibration to allow the device’s sensor to stabilize before you take relative humidity measurements in an area.

How to Calibrate an Analog/Humidor Hygrometer

How to Calibrate an Analog/Humidor Hygrometer

Analog hygrometers can be calibrated using a salt test

  • Put the device in an airtight container with a small dish of table salt and some water or moistened paper towel

The humidity inside the container should climb to between 70% and 80%. If not, adjust as needed by adding more salt or using less water. 

  • Write down the reading on the analog hygrometer once the humidity has stabilized at 70% to 80%. 
  • Now moisten some paper towels with distilled water and wipe off any excess moisture from outside your airtight container (otherwise, it will skew results). 
  • After wiping up extra moisture, put the device back in the container and close it up
  • If your hygrometer was reading too high (above 70%), put a few grains of salt on top of the paper towel inside your airtight jar. If it read low, add some water to increase the humidity between 70% and 80%. 
  • Leave closed for at least 48 hours, then recheck your analog hygrometer. If your hygrometer still reads low or high, repeat the process of adding/removing salt or water as needed. 

How to Calibrate a Hygrometer With a Wet Towel

How to Calibrate a Hygrometer With a Wet

The following way to calibrate a hygrometer is with an easy method that involves wetting the inside surface of a plastic bag. This technique works best for analog or digital models, and it’s better if you have two bags ready in case one gets too dry while waiting on readings. 

Since this test can take several hours, it’s essential to be patient.

  • To begin, wrap the hygrometer inside a wet towel and seal the bag with tape or plastic clips. 

For analog models, check readings after 12 hours; wait 24 hours before checking results for digital devices

  • Letting your unit sit in the sealed bag should cause humidity levels to hit 75 percent

If this is not the case, use a wet rag wrapped in plastic to increase humidity levels and check again after 12 hours have passed.

📌 If you get inaccurate readings even with high humidity inside the bag, your hygrometer may be damaged or defective and should probably be replaced. 

Using Small Glass Method

Using Small Glass Method

Using the small glass method is probably one of the easiest ways to calibrate a hygrometer. The calibration process for this method will only take about 30 minutes, which means you won’t have to spend too much time with it. 

  • Get a small glass or jar and fill it with saltwater until the surface of the water is approximated half an inch above the level of salts in solution.
  • Then, put your hygrometer in a well-ventilated area for about 15 minutes to allow dust particles that may have been collected on the hygrometer to settle.
  • Afterward, take the hygrometer out of the area and put it in a position where you can easily view both its display screen and that of your small glass or jar with salt water. 

Make sure there is enough distance between them, so you’re able to see both screens.

  • Put the saltwater in the small glass and look at your hygrometer’s display screen to see what its current humidity level is. 

Make a note of this number so you can compare it with an accurate reading later on. For example, if your hygrometer says that the humidity level is 70%, you write down 70.

  • After reading the number, turn your hygrometer off and then put some drops of water into the small glass with salt water on top of its surface but not touching it. 

The amount should be just enough to cover three-quarters of a quarter-inch above where salts are in solution. Make sure you only put enough water to cover this area.

  • Once you have put the right amount of drops, turn your hygrometer back on and wait for it to adjust itself accordingly by taking an accurate reading

If its humidity level is still within +/- one percent accuracy compared with what you wrote down earlier (which was 70%), then you’ve calibrated your hygrometer successfully.

Tips to ensure a successful calibration and humidity measurement

Tips to ensure a successful calibration and humidity measurement
  • Preventing false readings

Humidity is a measure of the water vapor in the air. If there isn’t any humidity, you will get incorrect readings because your equipment won’t detect anything. So make sure you are taking measurements during humid times.

  • Keeping your hygrometer away from heaters and air conditioners, as well as direct sunlight.
  • Use distilled water to test your hygrometer because tap water contains minerals that will throw off readings.
  • Choosing a time during which humidity levels remain relatively constant and consistent throughout the day/night cycle — a good choice would be in the morning when humidity levels are usually highest.
  • Choosing a spot that is free from wind (wind can affect your final reading and throw off calibration).

Summary

Calibrating a hygrometer is a very important step in ensuring accurate readings. If you ever purchase a new hygrometer, it should be calibrated before use. 

In addition, if you live in a humid environment, it is essential to calibrate your hygrometer more often than not. The most popular method for calibrating a hygrometer is to use salt and water. This method, however, should only be used if you are doing it for the first time or otherwise cannot remember how your previous calibration went (for example, because you didn’t write down any measurements).

If you know what readings should be expected at certain humidity levels, this type of calibration can be very accurate.

If you are looking for a quick fix, the salt and water method usually takes around an hour to complete. If you want something more precise, however, there are other methods (such as rubbing alcohol).

FAQ

📍 How to calibrate a hygrometer?

Salt and water are the most commonly used calibration methods for hygrometers, although there are other ways to calibrate them (such as with an oven). Those alternatives might be more accurate but will take a bit longer than using salt or water.

🗓 How often do you need to calibrate a hygrometer?

It depends on the conditions you are using it under. If you live in a humid environment (especially if your hygrometer is outside), then calibration should be done more often since the humidity levels will change constantly. However, if your readings are not fluctuating that much or the temperature changes very slowly, then once every few months might be enough.

📋 How do I know if my hygrometer is accurate?

If you are not sure how often to calibrate your device, the best way to find out whether it needs calibration or not is by looking at its past readings and comparing them with what other people report for similar conditions. If they match up pretty closely, it’s safe to assume that everything is good.

✔ What are the benefits of calibrating a hygrometer?

A properly calibrated hygrometer will provide you with more accurate readings, which can be very helpful if you are monitoring humidity for specific experiments or projects. It also ensures that your device functions correctly, which reduces the risk of any damage.

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