TH108 hygrometers have a hair sensing element or a membrane, so they are very sensitive to shakes and vibrations and their calibration is disturbed. After purchase, the th108 hygrometer needs to be calibrated. How to calibrate a th 108 thermohygrometer? To set up the th 108 hygrometer, we need a screwdriver and a wet rag in the first case. On the back of the hygrometer there are calibration screws that allow you to move the arrow in one direction or another. To know which direction you need to point the arrow, you need to have an idea of what the true value of humidity is at the time of calibration of the hygrometer. How to do it? The answer is simple on the one hand, and complicated on the other. To calibrate the hygrometer, you need to place the device in an environment with known humidity and adjust the readings. After setting in this environment, the hygrometer also displays the correct values when humidity changes. But the question arises: where to get such an environment? Another simpler way is to correct the readings of the new device according to the readings of the old, calibrated, standing next to the hygrometer. In this case, you will get more or less accurate readings, given the error that the old device had. However, there are two ways to create an environment with known humidity, based on physical laws. One method is fast enough, but not very accurate, the second, as you might guess, is long, but accurate. The first way. The hygrometer must be wrapped in a damp cloth, and then placed in a plastic bag. In a confined space, due to evaporation of moisture from a rag, the humidity in an hour will become 96%. You can more accurately determine that the humidity has reached its maximum value - the readings of even an un calibrated hygrometer will reach a certain value and stop changing. After that, remove the bag from the device and adjust the readings.
Hygrometer calibration with salt
For a more accurate calibration, prepare a saturated sodium chloride solution. This is done simply - pour salt in a saucer and drip water into it until completely dissolved. You can prepare the solution differently, heat a small amount of water, remove from heat and gradually dissolve the salt in the cooling water, until it precipitates. Next, cool the solution to room temperature and drain from the precipitate. Now place the appliance and saucer with salt in an airtight box. The essence of these actions is that in the presence of a saline solution of this concentration, air humidity is 75%. In order to establish such humidity, you will need patience - unlike the first method, you need to wait eight hours. After the waiting period, remove the device and set the arrow to 75%. This method is very accurate, in addition, the calibration was carried out at humidity values close to the middle of the range of use of the device, which also increases the confidence in the readings. Both of these methods will have a systematic error due to the fact that you remove the device from the environment with steady humidity. Therefore, it is very important to quickly install the readings after removing the hygrometer from the bag (in the first case) and the box in the second. You will have a maximum of a minute for all manipulations on tuning, after which the readings will change dramatically. After calibration, it is advisable to carefully install the device at a fixed location and not shake it, otherwise the calibration will fail, and now you already know how to calibrate the mechanical hygrometer.
Fast but inaccurate method.
Wrap the hygrometer in a damp cloth and place in a plastic bag. It is known that in a confined space with a large surface of evaporation of water, moisture evaporates until the humidity becomes approximately 96%. One hour will be enough for the humidity to reach this value. Then take out the hygrometer and set the needle to 96%.
A long but accurate method.
Place the hygrometer in an airtight box along with saturated sodium chloride solution. To do this, pour salt into the lid, and drip water there so that it is completely absorbed into the salt. It is known that next to saturated brine, humidity is 75%. Unlike the first method, it will take eight hours. Then take out the hygrometer and set the needle to 75%. This method is very accurate, plus the control point is closer to the range in which the device will be used. Therefore, after this procedure, the hygrometer can be completely trusted.
In both methods, it is very important not to pull with the arrows in the right position. As soon as you remove the hygrometer from the created environment, it will immediately begin to change its readings in the direction of humidity in your apartment. You will have a maximum of a minute, after which the hygrometer readings will change greatly. If you do not have time, you will have to carry out the procedure again.
Calibration of the hygrometer may fail due to shake or severe temperature changes. While the humidor is quietly standing on the shelf, the hygrometer will show the correct humidity for years, but after moving, for example, it is advisable to calibrate the hygrometer again.
Electronic hygrometers do not need to be calibrated; their factory calibration does not go astray.