Preh Automotive

Windshield Defogging Sensor

Suddenly having your windshield fog up is a commonplace, making visibility and safety a problem. When that happens, we struggle with countermeasures in the hope of removing the fog and keeping it away. These typically include activating blowers at a high level, which is noisy and increases fuel consumption, as well as raising the temperature to a higher level than intended or comfortable. The alternative is swiping at the windshield manually, only to have it fog over again.

Earlier defogging sensor systems have a disadvantage in common, that the interior temperature chosen by the driver directly influences when fogging occurs; but with infra-red sensors, there must already be fogging to initiate countermeasures, that means higher temperatures, higher energy consumption, noise – and you have fog anyway.

Preh Automotive began work to innovate ways to head off this common problem with countermeasures that might occur before the fogging itself does. Their approach was unconventional from the start, as it relied on capacitance-measuring technology, not optical or infrared technology. This new sensing technology determines the temperature and calculates relative humidity at the inner surface of the windshield, and then signals the climate control system to take measures to prevent fog on the windshield whenever needed. With direct and accurate measurement of relative humidity at the windshield, these problems disappear. Preventing the problem in the first place is quicker and therefore safer, more comfortable, and uses less energy than removing already-formed fog.

Preh’s capacitive sensor technology is directly applicable in ultra-small packaging to gauging rain or splatters on the windshield and initiating countermeasures, and to light penetration on temperature levels inside the cabin. In addition, it can’t be fooled by dirty or smeared windshields. Initial adoption of this innovative approach has been by BMW, starting with its new 5 Series, and by John Deere.