How do automatic windshield wipers on an automobile detect rain?

Question

where are the sensors typically located and how do they determine the intesity of the rain?

Answer 1

How it works: The most common rain sensor implementation is based on the prinicple of total internal reflection: an infrared light is beamed at a 45-degree angle into the windshield from the inside near the lower edge — if the glass is wet, less light makes it back to the sensor, and the wipers turn on. The intensity of the rain is determined by the amount fo IR light being reflected back - lots of water means little light reflected back and therefore, the wipers switch to a faster wipe mode.

Location: Typcially, the sensor is located at the top centre of the windshield - behind the rear-view mirror. This is mainly an aesthetic reason and the fact that it doesn't interrupt your vision from inside the car.

For more information on Total Internal Reflection, have a look at the Wikipedia site: http://en.wikipedia.org/wiki/Total_internal_reflection

Just a note to add - they do NOT work on vibration . . . if this were the case then there would be spurious "wipings" when a stone hit the screen . . . indeed, at faster speeds, small pieces of grit (heavier than a water droplet) are constantly impacting the screen!

Hope this helps!

Answer 2

Automatic Windshield Wipers

Answer 3

Hope this is not your situation, but I once made the mistake of applying Rain-x to my windshield and later washing the car with Mr. Clean no-dry car wash. The next time it rained I turned on the wipers and it looked like I was spreading white paint across the windshield. Both products are polymers (one trying to get water to bead up and the other trying to get it to sheet off) so trying to clean the windshield was hopeless. I got the smearing down to a level where we could drive by using Barkeeper's friend and an electric polisher for about half an hour. The problem lingered until the windshield had to be replaced because of a crack. Rain-x and Mr. Clean car wash are now banned from my garage.

Answer 4

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RE:
How do automatic windshield wipers on an automobile detect rain?
where are the sensors typically located and how do they determine the intesity of the rain?

Answer 5

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Best bet is to replace the blades. Ozone, UV rays, spray wax from carwashes, etc...all destroy wiper blades in a short amount of time. The big box stores like WalMart have them. Most Discount (ie: Autozone, O'Reilly, etc...)auto parts stores will change them for you at no additional cost. In the meantime you can try to decontaminate them with some rubbing alcohol and a clean lint free rag. Just wet the rag and run it down the rubber blade. Lots of black junk will come off and if it tears then it needed to be replaced anyway.

Answer 6

OH MAN! "INTESITY", WELL IT'S NOT THE WIPERS THAT DETECT THE RAIN. THEY ARE ACTIVATED BY SENSORS THAT DEETECT THE RAIN. THESE SENSORS DETECT VIBRATIONS THAT THE RAIN CAUSES. THE MORE RAIN, THE MORE VIBRATION, THE FASTER THE WIPERS WORK.