How do the rain sensors work?
Thread Starter
Senior Member
Joined: Aug 2004
Posts: 440
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From: Oakland, CA
2014 E350 Estate Wagon 4Matic
How do the rain sensors work?
Cheers.
Anyone here know what the "rain sensors" are doing? All it seems to be is an intermittent wiper switch. Is it supposed to go faster as there is more rain or slower if there's less? What gives?
Anyone here know what the "rain sensors" are doing? All it seems to be is an intermittent wiper switch. Is it supposed to go faster as there is more rain or slower if there's less? What gives?
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Joined: Mar 2003
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From: Greensboro, NC
00' ML 55 AMG; 08' Jeep Wrangler Unlimted (4 Door)
The Basics
The different optical rain sensors used in cars and trucks all use the same underlying principle. They bounce beams of light through the windshield, and look for disturbances in the beams cause by raindrops. Typically, a rain sensor will have an emitter that emits pulses of light, coupled into the windshield with a lens:
These beams travel through the windshield at about 45 degrees, depending on the details of the rain sensor design. In most cases, the beams are infrared. The beams are totally internally reflected by the outside surface of the windshield, so they bounce back into the sensor. A detector picks up the beams and measures them.
The electronics and software in the sensor turn on the wipers when the amount of light reflected onto the sensor decreases to a preset level. The software sets the speed of the wipers based on how fast the moisture builds up between wipes. It can operate the wipers at any speed. The system adjusts the speed as often as necessary to match with the rate of moisture accumulation.
The different optical rain sensors used in cars and trucks all use the same underlying principle. They bounce beams of light through the windshield, and look for disturbances in the beams cause by raindrops. Typically, a rain sensor will have an emitter that emits pulses of light, coupled into the windshield with a lens:
These beams travel through the windshield at about 45 degrees, depending on the details of the rain sensor design. In most cases, the beams are infrared. The beams are totally internally reflected by the outside surface of the windshield, so they bounce back into the sensor. A detector picks up the beams and measures them.
The electronics and software in the sensor turn on the wipers when the amount of light reflected onto the sensor decreases to a preset level. The software sets the speed of the wipers based on how fast the moisture builds up between wipes. It can operate the wipers at any speed. The system adjusts the speed as often as necessary to match with the rate of moisture accumulation.
Thread Starter
Senior Member
Joined: Aug 2004
Posts: 440
Likes: 44
From: Oakland, CA
2014 E350 Estate Wagon 4Matic
Man, liquid, that's one impressive response. Thanks. But mine don't stop after it stops raining. If I turn them on on a dry day, they just stay put, but if I turn them on after it's already rained, then they remain on. It's as if the rain drops which remain on the perimeter of the windshield are triggering the blades...
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From: Philadelphia area
2010 ML550, 2010 E350 4M, 1966 Corvette Convt C2
Originally Posted by hecdog
Man, liquid, that's one impressive response. Thanks. But mine don't stop after it stops raining. If I turn them on on a dry day, they just stay put, but if I turn them on after it's already rained, then they remain on. It's as if the rain drops which remain on the perimeter of the windshield are triggering the blades...
