Fog sensor or visibility sensor are devices that can detect the changes in weather, give warning or triggers when the visibility decreased in certain levels. Fog sensor basically consist of a light transmitter and a receiver.
Fog detection can be made in low costs and fast by using optical detection methods. There are two approaches to determine the fog. First one is measuring the light loss and second one is measuring the light scattering.
There must be a distance between light source and the light receiver to measuring the light loss. Light is transmitted from a certain point to the sensor. After that, the quantity of light is measured that reached to the sensor. The more the light is lost, the more the fog is, and the visibility is low in that sense. If the quantity of light reached to the sensor is high, then there is no fog, and the visibility is high.
The distance is not necessary to measuring the light scattering. Sensor should be placed a location that close to the light source but out of direct reach of the light. In this way, when the light turns on, the scattering light can be measured only. Fog-drip cause the light scattering. The presence of fog is detected by measuring the scattered light.
In both methods, there must be a powerful light source and precision receiver. The light source must be focused, and light intensity (lux) must be high. Complex optics might be needed to increase the light intensity. Lasers and LED light sources are commonly used in these applications.
If both systems are fictionalized correctly, they can become sensitive enough to detect shallow fog. Instead of visible light, infrared light is used detect the fog safely not only at night but when there is sunlight.
It should not be forgotten that fog sensors are extremely sensitive to dust, dirt, bugs, and spider webs. Because of these effects, devices that have self-calibrated systems that control contamination have been developed. However, the sensor should be checked and cleaned periodically.
Fog sensors are used in highways, tunnels, sea routes and air observation stations. The power consumption of fog sensors is very low. Therefore, it is possible to design self-contained systems operates with solar panel and battery without need of electrical supply.
