Temperature and humidity sensor how to choose the model

Temperature and humidity sensor how to choose the model? Temperature and humidity need to pay attention to the measurement range, accuracy of measurement, and drift and temperature drift when purchasing.

1. Select measurement range

Just like the measurement of weight and temperature, selecting the humidity sensor first determines the measurement range. In addition to the meteorological and scientific research departments, the measurement of temperature and humidity generally does not require full wet-range (0-100% RH) measurements.

2. Select measurement accuracy

The measurement accuracy is the most important indicator of the humidity sensor. For each increase of -1%, it is the previous step or even the previous level for the humidity sensor. Because to achieve different accuracy, the manufacturing costs vary greatly, and the price difference is very far. Therefore, users must tailor their clothing to avoid blindly pursuing “high, refined, and sharp”. If the humidity sensor is used at different temperatures, the indication must also consider the effect of temperature drift. It is well-known that relative humidity is a function of temperature and that the temperature affects the relative humidity in a given space. Each temperature changes by 0.1°C. A humidity change (error) of 0.5% RH will be generated. If it is difficult to use a constant temperature in the occasion of use, it is not suitable to propose excessively high humidity measurement accuracy. In most cases, the accuracy of ±5% RH is sufficient if there is no accurate temperature control method or if the space under test is unsealed. For those applications that require precise control of constant temperature, humidity, or humidity, or need to track and record changes in humidity at any time, use a humidity sensor with an accuracy of ±3% RH or more. Accuracy higher than ±2% RH is not even a standard humidity generator for calibration sensors, let alone the sensor itself. Relative humidity measuring instruments, even at 20-25 °C, to achieve 2% RH accuracy is still very difficult. The characteristics given in the general product literature are measured at room temperature (20 °C ± 10 °C) and clean gas.

3. Consider drift and temperature drift

In actual use, due to the influence of dust, oil, and harmful gases, the electronic humidity transmitter will age and the accuracy will decrease due to a long use time. The annual drift of the electronic humidity transmitter is generally about ±2%, and even more. high. Under normal circumstances, the manufacturer will indicate that the effective use time for one calibration is 1 year or 2 years, and it needs to be recalibrated upon expiration.

4. Other considerations

Humidity sensors are non-hermetic. To protect the accuracy and stability of measurements, they should be avoided in acidic, alkaline, and organic solvent-containing atmospheres. Also avoid using in dusty environments. In order 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 in a corner where air does not flow. If the room being measured is too large, multiple sensors should be placed. Some humidity sensors require a relatively high power supply, otherwise it will affect the measurement accuracy. Or the sensors can interfere with each other and they can't even work. When used, provide suitable power supply that meets the accuracy requirements according to technical requirements. When the sensor needs to carry out long-distance signal transmission, it is necessary to pay attention to signal attenuation. When the transmission distance exceeds 200m, it is recommended to use the humidity sensor of the frequency output signal.

In addition, there are some selection criteria. Due to different temperature and humidity measurement principles, temperature and humidity instruments are various. When selecting, users must consider the actual application environment and requirements of users, such as range, output and display, and installation methods. Sampling methods, gas types, materials and structures, control monitoring requirements, environmental hazards, etc. In addition, factors such as cost-effectiveness and maintenance workload should also be considered:

Cost-effective: When using temperature and humidity instruments, you can't just consider the price is low, you should choose the price and performance. This includes price, life, maintenance, and calibration costs. Verification: The method of verification and whether it is easy to consider, even if you do not need high-precision results. It will save you the workload of checking a convenient instrument on site and in situ.