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Need suggestions for a part

R_Phoenix

Hello all.

 

I am looking for the best option to detect when water is in a pipe. In a nut shell I 'm looking for a way to know when water is available inside a 3/4" pipe.

 

I thought of a pressure switch but I can't seem to find anything that is simple and in expensive and also there won't always be pressure on the switch, for instance when the water is flowing threw the pipe.

 

Then I thought of a flow meter, but again the water won't always be flowing to detect motion.

 

Now I am thinking of reading the capacitance/resistance of the water. I have a few options but I was wondering what else might be out there that I haven't stumbled on yet.

 

Thanks everyone.

  • Hi R,

     

    I think you're over thinking this. Since water conducts electricity, all you need is two conductors (non-corroding nails, or something that won't rust an contaminate the water supply). The two conductors form a switch, when no water is present the switch is open and no current flows. When water starts flowing in the pipe it will touch the two conductors and will allow current to flow from one to the other closing the switch.

     

    Two conductors and a pull-up resistor will give you a simple yes/no signal that you can feed to a microcontroller.

     

    hth,

    Jorge Garcia

  • in reply to Jorge_Garcia

    Thanks for the suggestion, I have in deed thought of that - however, it needs to be something I can bring to market. i.e. I can't just run 2 screws into a pipe image

     

    As you suggested, currosion is a problem, even with Stainless steel. I have some ideas on this as well, but before I spend time and money into prototyping, I want to evaluate any and all ideas.

     

    And hopfully find something that is already available.

     

    Thanks

  • Hi,  My question for you is, what is the PSI rating for the water system?  Pressure switch are about <$100 US. Have you thought of monitoring pipe temperature, as water flows the pipe temp will lower some.  Monitor two different locations to see if water is flowing.  Just an idea

     

    Dave M.

  • in reply to Jorge_Garcia
    Pure water is an insulator. A small amount of contamination, like salt, will make water conducting. Depending of the water used in your system the conductivity test will not work.
    For heavily contaminated water a conducting path could remain when the pipe is dry.
    For a pressure sensor you could use the pressure sensors used to control the water level in a washing machine. The older ones have contacts that can handle several amps. These sensors are installed above the water level and filled with air. They measure the pressure at the bottom of the  reservoir. Remember that soap is very aggressive.
    Another way is to use the thermal conductivity of the water.
    Place a small NTC or PTC resistor, electrically insulated, in the pipe not touching the wall.
    Heat up this resistor with a small current. If there is water in the pipe the temperature of the resistor will be much lower than when the resistor is surrounded by air. Measuring the Voltage over the resistor will show weather there is water or not. If the temperature of the water could be high, place a reference circuit on the wall of the pipe and create a wheatstone bridge circuit.

  • Have you considered using a piece of wire and a strain gage?  Once you set up the wieght of the pipe empty, you should be able to measure the added weight of any water to a fair degree of accuraccy.

     

    Just a thought.

    DAB

     

    PS, you might also get by with a microswitch.  It depends on how sensitive you need the indicator to be.

  • I had used a simple relative humidity sensor before by Honeywell.  The part was HIH-3610 that outputs a voltage level proportional to the supply voltage.  You might need to correct for environmental changes to humidity.  You would probably get a good  distinct reponse between the sensor element being wet or "dry" without having to do any corrections to the reading.

     

    Another idea, that might be a little tricky to implement would be some kind of "float" like you would find in a toilet, if there is water, a contact would float up and break contact with a switch, maybe a microswitch as was suggested earlier with something buoyant attached to a cantilever arm?

  • Wow, thanks for all the responses and good Ideas.

     

    My question for you is, what is the PSI rating for the water system?

     

    Have you thought of monitoring pipe temperature

    The PSI could go as high as 100+psi but would normally be around 60 to 80.

     

    Monitoring the pipe temp would be problematic if the water wasn't flowing at the time. Eventually the pipe would become "room temperature" if the water didn't flow but may be worth investigating further.

     

    Pure water is an insulator. A small amount of contamination, like salt, will make water conducting. Depending of the water used in your system the conductivity test will not work.
    For heavily contaminated water a conducting path could remain when the pipe is dry.

     

    This is true and something I hadn't considered - thanks. A lot of people will indeed be connecting things like filtration systems and De-ioniser so the conductive path may be problematic as well.

     

    Thanks for the other great Ideas everyone.

  • What about Ir? Would water in a pipe bend the beam enough compared to no water?

     

    Edit:

    A pressure switch won't work because when water is flowing there is no resistance to produce pressure on the switch so it would show open (no water).

  • Hello, There are several systems that could be employed 1) Conductivity, which is used in commercial water purification and typically indicates when the resistance is below 22 mohms, and unless specifically purified (DI, RO or distilled) all water will be below this value. 2) Thermal conductivity, measures how much power it takes to maintain a given temperature in an electrically heated probe. 3) Capacitance, which should give a large change in the absence of water. 4) IR, a simple infrared optoisolator should work as water is not very transparent to IR. 4) Density, measure the change in the frequency of a quartz crystal/ or sound conductivity between two piezoelectric elements, one driven and the other a sensor. 5) Refractive index of a bare fibre optic or again, just the change in the intensity of what light gets through to a photodiode. Conductivity and capacitance are widely used in industry. I'm guessing that these sensors can be inserted in the pipe, if not the thermal conductivity or density can be used external to the piping system. I can dig up circuits for these if interested

  • Hy there,

    if you can put the electronic inside the pipe you can make a resonant circuit with the capacitor on the pcp side located in direction to the water. and if water is present the capacitance will change and also the resonant frequency wich you can measure. This is how the water level sensor in coffe machines works.