Selection of Humidity Sensors The humidity sensor products of various manufacturers at home and abroad are of different levels, and the quality and price are quite different. How do users choose the ideal product with better performance and price? Â There is a certain degree of difficulty and you need to have an in-depth understanding in this regard.
The humidity sensor has the following features:
1. Accuracy and long-term stability The accuracy of the humidity sensor should reach ±0.1%~±0.8%RH. It is difficult to use this level as a measuring instrument. The humidity sensor should achieve ±2%~±3% RH accuracy. Difficult, usually the characteristics given in the product data are measured at room temperature (20 ° C ± 10 ° C) and clean gas. In actual use, due to the influence of dust, oil and harmful gases, the use time will lead to aging and the accuracy will decrease. The accuracy level of the humidity sensor should be judged by its long-term stability. Generally speaking, long-term stability and use Lifetime is the first problem affecting the quality of humidity sensors. There are few products with annual drift control at 1% RH level, generally around ±2% or even higher.
2. Temperature coefficient of humidity sensor In addition to sensitivity to environmental humidity, humidity sensor is also sensitive to temperature. Its temperature coefficient is generally in the range of 0.2~0.8%RH/°C, and some humidity sensors are under different relative humidity. The temperature coefficient is different. Temperature drift is nonlinear, which requires temperature compensation on the circuit. The humidity sensor using MCU software compensation or temperature compensation can not guarantee the accuracy of the full temperature range. The linearization of the temperature drift curve of the humidity sensor directly affects the compensation effect. The nonlinear temperature drift often does not compensate for the better effect. Only the hardware temperature follow-up compensation will be used to obtain the real compensation effect. The temperature range in which the humidity sensor operates is also an important parameter. Most humidity sensitive components are difficult to work properly above 40 °C.
3, the humidity sensor's power supply metal oxide ceramics, high molecular weight polymer and lithium chloride and other moisture sensitive materials when applying DC voltage, will lead to performance changes, or even failure, so this type of humidity sensor can not use DC voltage or DC components AC voltage. Must be powered by AC.
4. Interchangeability At present, humidity sensors generally have poor interchangeability. The same type of sensors cannot be interchanged, which seriously affects the use effect and adds difficulties to maintenance and debugging. Some manufacturers have made various efforts in this regard. Has achieved good results.
5. Humidity Correction Correcting humidity is much more difficult than correcting temperature. Temperature calibration often uses a standard thermometer as the standard, and the humidity calibration standard is difficult to achieve. Dry and wet bulb thermometers and some common pointer hygrometers cannot be used for calibration. The accuracy cannot be guaranteed because of the required environment. The conditions are very strict. In general, (in the case of a suitable humidity environment), in the absence of a complete calibration device, a simple saturated salt solution test is usually used and the temperature is measured.
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