Home generalCalibrate the hygrometer: this is how to calibrate it correctly

Calibrate the hygrometer: this is how to calibrate it correctly

  • Which hygrometers need to be calibrated "> Calibration methods
    • Calibrate hygrometer: damp cloth
    • Salt Method in the Pot: Instructions
    • Salt Method in Freezer Bag: Instructions

Hygrometers are among the most important instruments for measuring humidity. They are used for this purpose since the 18th century. Today's hygrometers are extremely accurate and are suitable for the industrial, private and hobby sector. When using a hygrometer accuracy is important. For this reason, it is necessary to periodically calibrate the hygrometer.

With a hygrometer you can quickly and effectively measure the humidity in your premises. The accurate measurement of humidity is suitable for a variety of applications. For example, if you need to adjust the humidity in the room to suit the needs of your plants, the hygrometer is an essential tool. You can see exactly how high the humidity is and act accordingly. The verification is also done with the hygrometer in the same way, which makes the use as a measuring device simple and effective. Over time, however, the measurement becomes less accurate, up to three percent. That means you have to calibrate the hygrometer.

Which hygrometers need to be calibrated?

When calibrating a hygrometer, you must pay particular attention to the type of instrument. Hygrometers are currently manufactured in a variety of types, some of which require calibration, while others do not, or rarely, maladjust:

  • Metal spiral (analog): must be calibrated
  • Natural hair (analog): must be calibrated
  • Synthetic hair (analog): does not need to be calibrated or only rarely calibrated
  • digital: do not need to be calibrated; Accuracy depends strongly on the quality

Natural hair is extremely stretchy and susceptible to moisture changes, while metal spirals simply disguise over time. With the digital hygrometers, a calibration is not really necessary, because everything works on the technology, but you should necessarily buy a high-quality model. A bad implementation immediately affects your measurement result, which would favor the acquisition of an analog model. Of these, models with synthetic hair are recommended. Due to the synthetic material they do not suffer from temperature fluctuations and can be used permanently. Depending on the type of hygrometer, this must be regularly maintained.

Tip: analog hygrometers must be calibrated twice a year to allow accurate measurement results. The reason: over the year they suffer from temperature and humidity fluctuations, which strongly affect the accuracy of the instrument.

Methods for calibration

Whether you use a hygrometer in your cigar humidor or conservatory, regular calibration is a must. If you do not want to take the meter to a specialist, there are three methods that you can use to calibrate the hygrometer yourself:

  • damp cloth
  • Salt method in the pot
  • Salt method in the freezer bag

These have proven themselves for decades and ensure that you have a calibrated hygrometer available within a short time. All methods make use of the function of the hygrometer. The device orients itself to the humidity it is exposed to and assumes this as the initial value. The methods allow such a value that the hygrometer can orient itself. Without it, it is not possible to calibrate the hygrometer and it deviates more and more from the previously set value. Use the instructions below to easily calibrate your instrument.

Tip: If your newly acquired digital hygrometer does not seem to be quite right, you just have to wait a bit. Despite the technology, the device must first get used to the room in which it is located.

Calibrate hygrometer: damp cloth

This method is one of the easiest ways to calibrate the hygrometer and is recommended by many manufacturers. The reason is the easy availability of the utensils and the simple but accurate calibration. Especially effective with this method is the speed, because compared to the pot method here a shorter period is needed. You need:

  • 1 towel made of cotton
  • 1 plastic bag in which the cloth fits

When choosing the towel, make sure that the hygrometer can be completely wrapped up and that no air can get into the unit. This is important because even the smallest changes in temperature affect the measurement result. Follow the procedure below:

Step 1: Select a room whose windows and doors can be closed in such a way that draft is prevented. Similarly, the room temperature should remain constant and not too cold. Make sure the temperature stays constant throughout. As noted above, minute changes in temperature immediately affect the meter and can result in an inaccuracy of three to four percent. Of course you want to prevent such a problem.

Step 2: Pick a flat surface on which to place the cloth. It is important that the hygrometer is straight, otherwise calibration errors can occur.

3rd step: Now moisten the cloth or alternatively a cloth and wrap the instrument in the fabric. Put the cloth in the plastic bag, especially if the surface is sensitive or should not get wet, and lay it on the surface.

4th step: The hygrometer must now remain unmoved for about two hours. During this time, the meter will focus on moisture and can be adjusted accordingly.

Step 5: After the two hours, carefully unpack the hygrometer and look at the display. It should now show 98 percent humidity . If this value is not displayed, which may well be, adjust the value yourself with the necessary adjustment screws.

Note: Immediately after removing the hygrometer, it should be calibrated, as it quickly adapts to the humidity in the room. So you have to hurry up when calibrating something.

Now the hygrometer is calibrated and can be used again.

Salt Method in the Pot: Instructions

The salt method in the pot is the most accurate way to calibrate the hygrometer. This variant is particularly time-consuming and you have to proceed exactly so that it does not come to errors when calibrating. You need:

  • Salt: 40 g per 1 l of water
  • water
  • cooking pot
  • Cling film
  • 1 glass that is not too high
  • 1 ruler

With this method, the room should have a constant temperature of 19 ° C to 21 ° C. Proceed as follows in the application

Step 1: Prepare the saline solution first. For this purpose, add so much water to the pot that the filling volume corresponds to a height of about 5 mm. Now add more and more salt until the salt can no longer be dissolved. The solution should look saturated and not too fluid.

Step 2: Now place the glass with the open side in the pot. If you want to be on the safe side, attach it with yarn so that it does not fall over. Put the hygrometer on the glass and make sure it does not touch or fall into the saline solution, otherwise it will be over.

Step 3: Now cover the pot with cling film airtight and let the pot rest for about four hours.

Step 4: After the four hours, the unit should show a relative humidity of 74 or 75 percent . If so, you can just take it out of the pot. If another value like the two mentioned can be seen, you must take the tool for adjusting the hygrometer in your hand. Carefully open the cling film and set the value to 74 or 75 percent within ten seconds. This has to happen so fast, because otherwise the values ​​can falsify.

Then the hygrometer is calibrated.

Salt Method in Freezer Bag: Instructions

The variant in the freezer bag is not quite as accurate as the one in the saucepan, but much simpler and shorter. For this you need:

  • 1 freezer bag
  • 1 tablespoon salt
  • water
  • 1 glass (small), for example shot glass
  • Rubber bands or sealing clips

In this variant, the room temperature must also be between 19 ° C and 21 ° C. Proceed as follows:

Step 1: Fill the salt into the glass and add water until the consistency is as good as a porridge. Put this together with the hygrometer in the freezer bag. Make sure that the hygrometer does not get into the porridge.

Step 2: Close the bag and let it rest for about two hours.

Step 3: The hygrometer should then display a value of 75 percent . If not, use the screws to change it. The advantage of this is that you do not have to remove the hygrometer from the bag as the screwdriver can operate the screws on the bag itself. This prevents a possible measurement inaccuracy.

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