Classification, Characteristics And Principles Of Humidity Sensor

Classification and characteristics of humidity sensors Humidity sensors are divided into resistance type and capacitive type. The basic form of the product is to coat a moisture-sensitive material on the substrate to form a moisture-sensitive film. Water vapor in the air

After being adsorbed on the humidity-sensitive material, the impedance and dielectric constant of the component change greatly, and the humidity-sensitive component of the desktop centrifuge is made. Humidity transmission of various manufacturers at home and abroad

Sensor products are of different levels, and there is a big difference in quality and price. It is indeed difficult for users to choose the ideal product with the best performance and price ratio.

In-depth understanding.

The humidity sensor has the following characteristics: 　　1, 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. The humidity sensor should reach ±2%~±

The accuracy of 3%RH is more difficult. Usually, the characteristics given in the product data are measured at room temperature (20℃±10℃) and clean gas. In actual use

In the medium, due to the influence of dust, oil and harmful gases, the use of time for a long time will cause aging and decrease in accuracy. The accuracy level of the humidity sensor should be combined with its long time.

In general, the working stability and service life of the humidity sensor inside the thermometer and hygrometer are the key to product quality. Generally speaking, the temperature and hygrometer,

The temperature is within ±1℃, and the humidity is within ±5%.

　　2. Temperature coefficient of humidity sensor 　　 In addition to being sensitive to environmental humidity, the humidity sensor is also very sensitive to temperature. Its temperature coefficient is generally within the range of 0.2~0.8%RH/℃, and some are humidity sensitive.

Components have different temperature coefficients under different relative humidity. Temperature drift is non-linear, which requires temperature compensation in the circuit. Using microcontroller software compensation,

Or a 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.

Linear temperature drift often cannot compensate for better results. Only by using hardware temperature follow-up compensation can the true compensation effect be obtained. The temperature at which the humidity sensor works

The degree range is also an important parameter. It is difficult for most humidity sensors to work normally above 40°C.

　　3. The power supply of the humidity sensor. 　　 When direct voltage is applied to humidity sensitive materials such as metal oxide ceramics, high molecular polymers and lithium chloride, it will cause performance changes and even failure, so this type of humidity

The degree sensor cannot use DC voltage or AC voltage with DC component. It must be powered by AC power.

　　4. Interchangeability　　 At present, humidity sensors generally have poor interchangeability. Sensors of the same model cannot be interchanged, which seriously affects the use effect.

The trial has increased the difficulty. Some manufacturers have made various efforts in this regard (but the interchangeability is still very poor) and achieved good results.

　　5. Humidity correction 　　 It is much more difficult to correct humidity than to correct temperature. Temperature calibration often uses a standard thermometer as the standard, while the humidity calibration standard is difficult to achieve.

Wet bulb thermometers and some common pointer hygrometers cannot be used for calibration, and the accuracy cannot be guaranteed, because they require very strict environmental conditions. In general,

(Preferably under the conditions of suitable humidity environment) In the absence of complete verification equipment, usually simple saturated salt solution verification method and digital display high-temperature sterilization pot are used to measure

Measure its temperature.