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Thread: Help with wiring my sensor

  1. #1
    Automated Home Guru neilhooper's Avatar
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    Default Help with wiring my sensor

    Hi All,

    I have a water flow sensor that has the following spec:

    •Pulse output frequency (Hz)= 4.1 x Q where Q=volume flow rate in L/min
    •Connections: RED (positive), BLACK (negative), YELLOW (output signal)
    •Voltage rating: 3Vdc to 18Vdc at 15mA
    •Output rating 18Vdc 30mA open collector (recommended 4k7 pull-up resistor)

    I have several QRI's that can take a pulsed input however, I'm not sure about the wiring as other pulsed sensors I've got only use two wires and don't use a resistor.

    Can anybody suggest a detailed way of wiring this in ?

    - Neil

  2. #2
    Automated Home Legend chris_j_hunter's Avatar
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    sounds like it gives an analogue rather than pulse output ...

    sounds interesting - which one would it be ?

    Chris

  3. #3
    Automated Home Legend Karam's Avatar
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    Sounds like a non isolated pulsed output. You could connect it to a QRI in the following way:

    Black to 0V on QRI IDRANet connector
    Red to 12V on QRI IDRANet connector
    Yellow to Digital input. The pullup resistor already exists in the QRI.

    Might be worth checking before connecting the yellow wire (but with red and black connected) that there is no voltage >3.3V measurable between yellow wire and 0V ... just in case 'open collector' is not entirely true. You need to run the water such that the signal is changing to ensure you capture any 'high' state.

    Don't know what maximum flowrate you expect but the pulse counting inputs are not designed for high frequency signals so 5l/min should be ok but 10 might not be. Also you will probably need to set the meter sample period to the 10-15s area.
    Last edited by Karam; 19th September 2012 at 06:10 PM.

  4. #4
    Automated Home Guru neilhooper's Avatar
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    Karam,

    I've wired it up as per your suggestion and I've checked the yellow wire and I'm getting approx 5.5v with fluctuations of +/- 0.1v.

    Does this mean that I can't use it with a QRI or do I need to limit the voltage coming through the yellow wire with perhaps a resistor in series?

    - Neil

  5. #5
    Automated Home Legend Karam's Avatar
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    Could be due to some minor leakage current from somewhere. If you have a 4k7 resistor or higher and connect this between the yellow wire and 0V then measure voltage at yellow wire again, if this is now found to be close to 0V then you'll likely be ok for a direct connection (having taken away the test resistor). But if you want to be on the safe side I'd suggest a schottky diode such as BAT85 or SD103A (Farnell 1612341) pointing from digital input to the yellow wire. Low voltage drop of a Schottky is better to ensure that the voltage drops low enough at the digital input (Diode drop + collector drop ideally <0.8V).

  6. #6
    Automated Home Guru neilhooper's Avatar
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    Karam,

    I've been playing this morning and connected the resistor and I'm now getting 2.65v; is this low enough or do I need the diode, if so can I use a BAT43 instead as I can pop to Maplins and get one of those. If I get the 85 from Farnel etc I have to buy 10 and wait until I can make up the minimum order value. If the 43 is not suitable could you advise what I'm looking for on minimum and maximum spec if that's possible so I can maybe source one locally that will work. I hope I've explained that properly.

    - Neil

  7. #7
    Automated Home Legend Karam's Avatar
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    A BAT43 should be fine. Banded end to yellow wire.

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