Caustic Corrosion on water level sensor

Discussion in 'The Projects Forum' started by bhargav shankhalpara, Apr 13, 2015.

  1. bhargav shankhalpara

    Thread Starter Member

    May 9, 2010
    18
    0
    Hello All..!!

    I am working on project water level controller. in that for water level detection i used three sensors shown in image. which is made up of stainless steel as well as mild steel.

    i am using three sensors, one at bottom of tank which work as common. second at middle of tank, and third is at top of tank. in bottom sensor (work as common) i give DC 5V.

    When i get 5 volt in both middle and top sensor we assume it as full tank, when not getting 5v at middle and top i assume tank is empty.

    my problem is that when we install system at our farm its working perfectly, but after a week its start malfunction. when we see sensors which we have installed at top tank, there is Caustic Corrosion around common sensor in which we give DC 5V. thats why its not working properly. after that i cleaned common sensors and connect again its working fine.

    is there any solution by which we avoid this type of Caustic Corrosion around sensor....??

    Please suggest solution

    thank you..!!

    [​IMG]
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,664
    634
    Try driving it with AC so that there is zero net volts between the probe and the other electrode. That's what's done in ph meters.
     
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  3. Nykolas

    Member

    Aug 27, 2013
    87
    31
    And across end-of-line resistors in supervised systems. E
     
  4. #12

    Expert

    Nov 30, 2010
    16,355
    6,852
    That is not caustic corrosion. It is a deposited coating caused by electrolysis of the dissolved solids. Use AC to drive the probes for net current = zero. Square waves work nicely.
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    As pointed out, the excitation for the sensor must have no DC component (must have a blocking capacitor in series with the sensor). The amplitude of the excitation should be less than 1Vpp. To see why, look at an electromotive series table
     
    #12 likes this.
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,381
    Wouldn't three float switches work better?
    If you just want three different levels?
    Max.
     
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