Selection of Temperature and Humidity Sensor

The following precautions should be paid attention to when selecting the temperature and humidity sensor:

Select measurement range

Like measuring weight and temperature, the selection of humidity sensor must first determine the measurement range. Except for the meteorological and scientific research departments, those engaged in temperature and humidity measurement and control generally do not need full humidity range (0-100% RH) measurement.

Select measurement accuracy

The measurement accuracy is the most important indicator of the humidity sensor. Every increase of one percentage point means a higher level, even a higher level, for the humidity sensor. Because to achieve different accuracy, the manufacturing cost and selling price vary greatly. Therefore, users must tailor their clothes and should not blindly pursue "high, fine and sharp". If the humidity sensor is used at different temperatures, the influence of temperature drift should also be considered in its indication.

As we all know, relative humidity is a function of temperature, which seriously affects the relative humidity in a designated space. Every 0.1 ℃ change in temperature. Will produce a humidity change (error) of 0.5% RH. If it is difficult to achieve a constant temperature in the application occasion, it is inappropriate to put forward too high humidity measurement accuracy. In most cases, if there is no accurate temperature control means or the measured space is not sealed, the accuracy of ± 5% RH is sufficient.

For local spaces that require precise control of constant temperature and humidity, or where humidity changes need to be tracked and recorded at any time, humidity sensors with an accuracy of more than ± 3% RH shall be selected. The requirement of accuracy higher than ± 2% RH may be difficult for the standard humidity generator to calibrate the sensor, not to mention the sensor itself. It is still difficult for the relative humidity measuring instrument to reach the accuracy of 2% RH even at 20-25 ℃. Generally, the characteristics given in the product data are measured at room temperature (20 ℃ ± 10 ℃) and in clean gas.

Consider time drift and temperature drift

In actual use, due to the influence of dust, oil, and harmful gases, the electronic humidity sensor will be aged and the accuracy will be reduced after a long time of use. The annual drift of the electronic humidity sensor is generally about ± 2%, or even higher. Generally, the manufacturer will indicate that the effective use time of one calibration is 1 year or 2 years, and it needs to be recalibrated when it expires.

Other precautions

The humidity sensor is nonsealed. To protect the accuracy and stability of measurement, it should be avoided used in acidic, alkaline, and organic solvent-containing atmospheres. Also, avoid using it in a dusty environment.

To correctly reflect the humidity of the space to be measured, it is also necessary to avoid placing the sensor too close to the wall or at a dead corner where the air is not circulating. If the measured room is too large, multiple sensors should be placed.

Some humidity sensors have high requirements for power supply, otherwise, the measurement accuracy will be affected. Or the sensors interfere with each other and even fail to work. When in use, a suitable power supply meeting the accuracy requirements shall be provided according to the technical requirements.

When the sensor needs long-distance signal transmission, we should pay attention to the attenuation of the signal. When the transmission distance is more than 200m, it is recommended to select the humidity sensor with the current output signal.

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