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Rain sensing Wipers

Discussion in 'Electrical Systems' started by sungoa2010, Dec 3, 2012.

  1. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    Our 2012 Linea is coming with Rain sensing wipers. Let us see how it is working. The below figure will explain the function


    rainsensing.jpg

    Whenever light falls on a reflecting surfaces like glass both reflection and transmission happens. But at some critical angle the entire light reflected back which is called total internal reflection(TIR). This we have studied in school. But this critical angle simply depend on the optical property of the reflecting surface(refractive index) of the reflecting medium.

    Cars with Rain sensing wipers use this property. They use a infrared source emit the radiation which is fixed in such a way that for given dry condition total internal reflection happens. So a receiving sensor will record max intensity. How it is detecting Rain. Wait as I told earlier the TIR will depend on optical property of surface. When the surface become wet the optical property(RI) changes and for the fixed orientation of IR source TIR will not happen so some intensity will be lost as trasmission through glass and the sensor will record lesser intensity. This property can be use to measure the intensity of Rain. more rain means more deviation from the dry condition. This is the basic property and rest of the things is a electronic or wireless circuit that integrate this with wiping action. So this is what happening in our cute Linea when it is raining. This is not a Fiat innovated technology. It was the GM which introduced rain sensing technology in cars.

    If water can change the optical properties so a film also. So pasting films on front windshield it will alter the optical properties. The films have different refractive index than windshield glass. So there is a possibility that Rain sensing wipers will malfunction if such a films are pasted on front wind shield. It is a possibility amd I am not telling this will happen.


    • Now my next concern is where this sensors are kept IN OUR CARS?

    • Is it the same technology that is used in Fiats or any other type of sensing? The falling rain drops give rise to pressure waves on windshield which should be also detectable.

    If you have more to share about Rain sensing wipers please share it here for our better understanding.
    -Sunil
    6 people like this.
  2. jayakrishnakola

    jayakrishnakola Regolare

    Messages:
    439
    Bangalore
    the sensor is just behind the hinge where the internal rear viw mirror is mounted.......
    5 people like this.
  3. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    Thanks for the information.
  4. mvb4u

    mvb4u Regolare

    Messages:
    384
    AndhraPradesh
    Guntur
    Grande Punto 1.3
    Sun what is that small button like thing on the dash board where windshield meets the dash board?

    I remember somewhere I read it is Automatic Climate Control internal temperature sensor. Can you clarify this?
  5. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    I also think so. Not sure exactly.
    May be one can keep a plastic sheet and a icream cup over it and test whether MID shows temperature of Shimla:D
    4 people like this.
  6. amargawade90

    amargawade90 Superiore

    Good Info...Sirr @sunil bhai !! :cool:

    - - - Merged Post - - -

    Lolzz.....:evilsmile
    Last edited: Dec 3, 2012
    1 person likes this.
  7. Sun,

    Your thinking is very creative.
    1 person likes this.
  8. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    Below is some few tests to understand the action of rain sensing wiper.

    1. Keep the rain sensor in active position switch on the engine keep the car in neutral and pour a glass of water at different places of glass to see how the wiper responding.

    2. Once we find the position which is sensitive to rain drops keep a plastic sheet sheet on that position from inside of the car to see the lack of sensing the reflected light activate the wiper in action. Please don't do it from out side since it will spoil your wipers if it get activated. If it works then it is a good science demo for your school going kid :)

    3. Why I am interested in item 3 is the following. We have read in this forum about dacoits throwing egg on screen to stop the vehicle. If the driver switch on the vehicle it block the front visibility. One should drive with wiper in off position without stopping the vehicle. Now let us consider car with rain sensing wiper. If the scattered egg activate the wiper it will be disastrous. If the test suggested above shows such activation is possible then one should deactivate the rain sensing option while travelling in such highways.

    - - - Merged Post - - -

    Thanks Sat.
  9. Viny

    Viny Esperto

    Messages:
    1,742
    :)
    Well generally i dont have any fondness towards rain sensors, as i can see rain and can decide when do i want to have wipers on. Probably hill climb assist is much better feature as compared to that. Having said that, the point raised by Sungoa is valid, if rain sensors react to eggs (which for sure was never considered as test input by designers) then it could be troublesome. I understand a shop water helps to get over it, so pouring required windshield cleaner liquid in the container could be good idea.
    1 person likes this.
  10. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    I also not a big fan of RS. One can switch on the wiper with one finger. But where it handy is to increase and decrease wiping speed according to intensity of rain. Especially in Konkan region where there is a heavy rain falls. Many times the intensity of rain fluctuate and changing the speed of wiper will be quite irritating.

    One disadvantage is after a long drive with full of dust on windshield and if wiper come in to action by spreading the paste of dust like a cheese spread. I would rather drive slowly allowing some more water to get collected on windshield so that most of the dust to get wiped out by rain and then switch on the wiper.
    1 person likes this.

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