Physical Backgrounds. Hygrometer with a conductive film - design, advantages, disadvantages.
Absorbed by certain materials, water can affect the electrical properties of these materials. This phenomenon is at the heart of the hygrometer with a conductive film. Depending on the humidity of the air (gas) in hygrometers with a conductive film changes the electrical resistance of the film - the sensor hygrometer.
This type of hygrometer measures the relative humidity of the air, which is a major advantage, as the relative humidity is very weakly dependent on temperature. The disadvantage is the need to calibrate each hygrometer and high stability of this calibration. Calibration can be displaced as a result of deposition of ions on the film during its contact with dust and other components of the gas. Furthermore hygrometer is not a high output power, which is also a disadvantage. The signal strength of the hygrometer can be increased sensor size increases, but the performance is lost, there is hysteresis.
Hygrometer with a conductive film consists of a sensor - layer hygroscopic substance deposited on an insulating substrate. As a hygroscopic substance (hygrometer sensor) often use certain metal oxides, and other materials. Electrical contacts are made, usually in the form of a comb. With increasing gas humidity and therefore sensitive film its electrical resistance decreases. Dependence in most cases is exponential.
Hygrometer with a conductive film has a fairly short response and is often used to determine the moisture content of small values of air (gas).