PCB Tech - The relationship between 5 characteristics of humidity sensor and ceramic substrate

The relationship between 5 characteristics of humidity sensor and ceramic substrate

1, the temperature coefficient of the humidity sensor
Humidity sensors can collect data mainly through humidity-sensitive components. In addition to being sensitive to environmental humidity, humidity-sensitive components are also very sensitive to temperature. The temperature coefficient is generally in the range of 0.2~0.8%RH/ degree Celsius, and some humidity-sensitive components are in the range of 0.2~0.8%RH/ degree Celsius. Under different relative humidity, the temperature coefficient is different. At this time, the advantages of the ceramic substrate can be highlighted. The thermal conductivity of the ceramic substrate is very high, which can maintain the temperature of the humidity sensor in a stable state for a long time.
2, accuracy and long-term stability
The accuracy of the humidity sensor should reach ±2%~±5%RH. If this level is not reached, it is difficult to use it as a measuring instrument. It is difficult for the humidity sensor to achieve an accuracy of ±2%~±3%RH, usually in the PCB product information. The characteristics given are measured at room temperature (20 degree Celsius±10 degree Celsius) and clean gas. In actual use, due to the influence of dust, oil and harmful gases, long-term use will cause aging and accuracy degradation. The accuracy level of the humidity sensor should be judged in conjunction with its long-term stability. Generally speaking, long-term stability and use Life is the top issue that affects the quality of the humidity sensor. There are very few products whose annual drift is controlled at 1%RH, generally around ±2% or even higher. Ceramic substrates that can maintain the annual drift at 1%RH are those that use ceramic substrates. Ceramic substrates have strong mechanical strength and can withstand strong acids and alkalis, providing the most perfect protection for the humidity sensor.

3, the power supply of the humidity sensor
Moisture sensitive materials such as metal oxide ceramics, high molecular polymers and lithium chloride will cause performance changes and even failure when DC voltage is applied. Therefore, such humidity sensors cannot use DC voltage or AC voltage with DC components. It must be powered by AC power.
4, humidity correction
Correcting humidity is much more difficult than correcting temperature. Temperature calibration often uses a standard thermometer as the standard, while the humidity calibration standard is difficult to achieve. Dry and wet bulb thermometers and some common pointer hygrometers cannot be used for calibration, and the accuracy cannot be guaranteed because of the environmental requirements. The conditions are very strict. Generally, (preferably under the conditions of suitable humidity environment), in the absence of complete verification equipment, a simple saturated salt solution verification method is usually used and the temperature is measured.
5. Interchangeability
At present, humidity sensors generally have poor interchangeability. Sensors of the same model 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, but the interchangeability is still Very bad.
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