How to choose a humidity sensor

Abstract: The information on how to choose a humidity sensor is provided by the excellent flowmeter and flowmeter production and quotation manufacturers. With the development of the times, scientific research, agriculture, HVAC, textile, computer room, aerospace, electric power and other industrial sectors are more and more required to use humidity sensors, and the requirements for product quality are getting higher and higher. As well as for industrial materials water. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of how to choose a humidity sensor. With the development of the times, scientific research, agriculture, HVAC, textile, computer room, aerospace, electric power and other industrial sectors are more and more required to use humidity sensors, and the requirements for product quality are getting higher and higher. And the monitoring and analysis of the moisture value of industrial materials has become one of the more common technical conditions. Humidity sensor products and humidity measurement belong to the industry that emerged in the 1990s. How to use the humidity sensor well and how to judge the performance of the humidity sensor is still a relatively complicated technical problem for ordinary users. The following article is for your reference. 1. Classification of humidity sensors and characteristics of humidity sensing Humidity sensors are divided into two types: resistive type and capacitive type. The basic form of the product is to coat a humidity-sensitive material on the substrate to form a humidity-sensitive film. After the water vapor in the air is adsorbed on the moisture-sensing material, the impedance and dielectric constant of the element change greatly, thereby making a moisture-sensing element. The humidity sensor products of various domestic and foreign manufacturers have different levels, and the quality and price vary greatly. It is indeed difficult for users to choose the ideal product with the best performance and price ratio. The humidity sensor has the following characteristics: 1. Accuracy and long-term stability The accuracy of the humidity sensor should reach±2%~±5%RH, it is difficult to use as a measuring instrument if it cannot reach this level, and the humidity sensor must reach±2%~±The accuracy of 3%RH is more difficult, usually the characteristics given in the product data are at normal temperature (20℃).±10°C) and in clean gas. In actual use, due to the influence of dust, oil pollution and harmful gases, aging and accuracy will occur over a long period of time. The accuracy level of the humidity sensor should be judged based on its long-term stability. Generally speaking, long-term stability and use Life is the primary issue affecting the quality of the humidity sensor. There are very few products whose annual drift is controlled at the 1%RH level.±2%, or even higher. 2. The temperature coefficient of the humidity sensor is not only sensitive to environmental humidity, but also very sensitive to temperature. Its temperature coefficient is generally in the range of 0.2~0.8%RH/℃, and some humidity sensors are under different relative humidity. , and their temperature coefficients are different. The temperature drift is nonlinear, which requires a temperature compensation formula to be added to the circuit. The use of microcontroller software compensation, or the humidity sensor without temperature compensation cannot guarantee the accuracy of the full temperature range. The linearization of the temperature drift curve of the humidity sensor directly affects the compensation effect, and the nonlinear temperature drift often cannot compensate well. , the real compensation effect can be obtained only by adopting the hardware temperature following compensation. The temperature range in which the humidity sensor operates is also an important parameter. It is difficult for most humidity sensitive components to work normally above 40°C. 3. The power supply of the humidity sensor When DC voltage is applied to humidity-sensitive materials such as metal oxide ceramics, polymer polymers and lithium chloride, it will cause performance changes or even failure. Therefore, such humidity sensors cannot use DC voltage or DC components. AC voltage. Must be AC ​​powered. 4. Interchangeability At present, humidity sensors generally have poor interchangeability. Sensors of the same type cannot be interchanged, which seriously affects the use effect and makes maintenance and debugging more difficult. Some manufacturers have made various efforts in this regard. (but still poor interchangeability) achieved good results. 5. Humidity Correction Correcting humidity is much more difficult than correcting temperature. Temperature calibration is often done with a standard thermometer, while the humidity calibration standard is difficult to achieve. Wet and dry bulb thermometers and some common pointer hygrometers cannot be used for calibration, and the accuracy cannot be guaranteed because of the required environment. The conditions are very strict. In general, (preferably in a suitable humidity environment), when there is a lack of perfect verification equipment, a simple saturated salt solution verification method is usually used, and its temperature is measured. 2. Several methods for preliminary judgment of the performance of the humidity sensor In the case that the actual calibration of the humidity sensor is difficult, some simple methods can be used to judge and check the performance of the humidity sensor. 1. Consistency determination. It is best to purchase more than two humidity sensor products of the same type and the same manufacturer at a time. The more the humidity sensor products are, the more the problem will be explained. Put them together and compare the detected output values. Under relatively stable conditions, observe the consistency of the test. . For further testing, it can be recorded at intervals of 24 hours. Generally, there are three humidity and temperature conditions of high, medium and low in one day, and the consistency and stability of the product can be observed more comprehensively, including temperature compensation characteristics. 2. Humidify the sensor with your mouth or use other humidification methods to observe its sensitivity, repeatability, humidification and dehumidification performance, resolution, and the highest range of the product. 3. Test the product in both cases of opening and closing the box.

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