Water detection. As problem solved


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  1. #1
    Fanatical Contributor Tim's Avatar
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    Default Water detection. As problem solved

    Those with a long memory may remember my attempts at detecting water in a tube.

    I got to a position where I thought I had it licked using probes 5v a resistor and adc converter.

    All was well until purified water was used

    Advice was taken on using AC at the probe etc. All appreciated.

    I got round to looking at it again and talked with a friend. He came up with a single chip solution It uses a cmos 4093 schmitt device. One gate provides the AC and another the extremely low impedance the device needs to turn on.

    Attached is a basic schema if anyone is interested. In my system it will run on 12v with an R/R divider to cap the output to the 3.3v I need and use another gate so I can have 2 probes.

    Cheers

    TimClick image for larger version

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    Tim

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    Prolific Poster rcurl's Avatar
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    Default Re: Water detection. As problem solved

    Nice solution. Thanks, Tim!

    -Rick

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    Default Re: Water detection. As problem solved

    Well done Tim.

    Mine is not much different while I use the CD40106 (1 gate) Hex-Schmitt-trigger, CD4093 have 2 gates but if you ties this together, then it is also one gate.

    But keep in mind, don't route AC-lines (120VAC-240VAC) close to the sensor, but at distance!
    And as suprice, water conduct EM-fields better than air!

    Second suprice CD40106 runs from 3V.

    Henk.
    Last edited by Henk57; 14th November 2016 at 15:53.

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    Fanatical Contributor Tim's Avatar
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    Default Re: Water detection. As problem solved

    Hi Henk

    I went for 12v as I had it but also because I have the diode thresholds to overcome. Thanks for the warning about the 120-240v nearby. The equipment will be in a metal case and feed 12vdc so hope I will be OK.

    Tim
    Tim

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    Member John Lawton's Avatar
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    Default Re: Water detection. As problem solved

    Also a long lenth of sensing cable has significant capacitance which appears to the circuit as a resistance leak, so basically this system is okay with short cables.

    John

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    Fanatical Contributor Tim's Avatar
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    Default Re: Water detection. As problem solved

    The cable length will be no more than 75mm from the board to the probes and the ground on the tube.

    I have 2 probes one at the bottom and one at the top. whole system is in a metal enclosure and 12v dc power in. There is a fan that is PWM'ed though and in the past it made a hell of a lot of noise. But an inductor and big cap sorted it.

    Its one of those projects that if I get it sorted will be worth a lot of money. If only I had the time to finish it! Just to busy making a living to find the time

    Cheers

    Tim
    Tim

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