[WapCar] Rain-sensing wipers detect the presence and amount of rain by using rain sensor, then automatically adjust the speed and frequency of the blades according to the amount of rain detected, and provide the driver with a good view, thereby greatly improving the convenience and safety of driving in rainy days.
At present, there are two kinds of inductive wipers: optical sensor and capacitive sensor.
Working Principle
Optical sensor works according to the principle of light refraction. There is a light-emitting diode in the optical sensor, which emits a cone of light that passes through the front windshield. When the windshield is in a dry state, almost all the light will be reflected on an optical sensor. When it rains, there will be rain on the windshield, and part of the light will deviate, which causes the sensor receives a change in the total amount of light, thereby detecting the presence of rain. The larger the area of the optical sensor that can receive the reflected light, the more detailed information it can obtain. The optical sensor is very accurate, and it is even possible to accurately determine the number of raindrops falling on the sensing area.
The other is a capacitive sensor, which is designed mainly by using the huge difference in the dielectric constant of water and glass. The dielectric constant of water is 80 and the dielectric constant of glass is 2. The usual practice is to put two parallel finger-shaped metal plates between the inner and outer layers of the windshield, a set of finger-shaped metal plates are interlaced, but they do not touch the other finger-shaped metal plates. When the windshield is in a dry state, a dielectric is formed between the outer surface of the windshield and each set of finger-shaped metal plates. When the windshield becomes wet, the dielectric constant of the windshield changes differently depending on the amount of water in contact with the windshield. If the sensor is installed on the surface of the windshield or close to the lower surface of the windshield, this is beneficial to the work of the sensor, because such an installation can make the sensor play its best sensitivity. Disadvantageously, installing the capacitive sensor on the outer surface of the windshield will cause the same problem as the resistance sensor, and its metal coating will be quickly scraped off the windshield under the long-term operation of the wiper.