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The Development Trend Of Humidity Sensor

In the industrial and agricultural production, weather, environmental protection, national defense, scientific research, aerospace and other departments are often required to measure and control humidity. However, in conventional environmental parameters, the humidity is the most difficult to accurately measure a parameter. With the dry and wet bulb hygrometer or a hair hygrometer to measure humidity, the method has long been unable to meet the needs of the development of modern science and technology. This is because the measurement of humidity than the measurement of complex multi-temperature, the temperature is measured is an independent, while the humidity is affected by other factors (atmospheric pressure, temperature) effects.

    In addition, the calibration of humidity is also a problem. Production abroad humidity calibration equipment prices are very expensive.

    In recent years, the humidity sensor research and development at home and abroad have made great strides. Humidity sensor is moving from simple humidity sensor to the integrated, intelligent, multi-parameter detection of the direction of rapid development, in order to develop a new generation of humidity / temperature measurement and control system has created favorable conditions for humidity measurement techniques will also be raised to a new level.

    The characteristics of humidity sensor

    Humidity sensor is the simplest humidity sensor. Humidity sensor are mainly resistive, capacitive two broad categories.

    a humidity sensitive resistor

    Humidity resistance is characterized by the substrate covered by a layer of wet material with a sense of the film, when the air in the water vapor adsorbed on a sense of the wet membrane, the components of the resistivity and resistance values are changed to use this feature Humidity can be measured. Many different types of humidity resistance, such as metal oxide humidity resistance, humidity resistance of silicon, ceramic humidity resistance and so on. Humidity resistance has the advantage of high sensitivity, the main drawback is that linearity and interchangeability of products poor.

    b Humidity Capacitance

    Humidity capacitors are generally made with the polymer film capacitors, polymer materials commonly used in polystyrene, polyimide, cellulose acetate, etc. butyricum. When the ambient humidity changes, the capacitance of the dielectric constant humidity changes, so that it is also a change in capacitance, its capacitance is proportional to the change in relative humidity. The main advantage of capacitive humidity sensor with high sensitivity and product interchangeability is good, fast response, a small amount of moisture lag, easy to manufacture, easy to achieve miniaturization and integration, and its accuracy in general is lower than the humidity sensitive resistor. The main production abroad humidity capacitor manufacturers are Humirel company, Philips Company, Siemens Corporation. To Humirel produced SH1100-type humidity sensor capacitor, for example, the measurement range is (1% ~ 99%) RH, at 55% RH when the electrical capacity of 180pF (typical value). When the relative humidity from 0 to 100%, the changes in capacitance range is 163pF ~ 202pF. The temperature coefficient of 0.04pF / ℃, humidity hysteresis amount of ± 1.5%, response time of 5s.

    In addition to resistive, capacitive humidity sensor, there are ionic-type humidity sensor, weight-type humidity sensor (with a sense of the changes in the weight of wet film to change the oscillation frequency), light intensity-type humidity sensor, SAW humidity sensor and so on.

    Humidity sensor linearity and anti-pollution poor in the detection of ambient humidity, the humidity sensor to a long-term exposure to the environment under test, it is easily affected by pollution, measurement accuracy and long-term stability.
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