Water and object detecton

Discussion in 'General Electronics Chat' started by mathew086, Aug 27, 2009.

  1. mathew086

    Thread Starter New Member

    Aug 27, 2009
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    Hello

    I am trying to use a sensor that could give a signal when both water and objects flow thorugh a pipe.

    The following are the options i found optimal:

    1) IR LED & Photodiode: Placing the IR LED and Photodiode at opposite one sides. When objects come in between them, the photodiode receives no light and the output will be zero. When water comes in between them there will be refraction of llight in water and so the light may not fall directly to the photodiode.


    2) Using Resistants :
    To detect change in resistance when objects or water comes in between the sensing probes.

    Can anyone suggest other methods that could sense both water and objects? Will there be any problems if i use the above mentioned methods? ( any negative impacts?)

    I do not want to invest much money by buying commercial sensors.

    Thanks for any comments
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Is the pipe plastic or metal? Are the objects metal or non-metal?

    Have you considered capacitance?

    John
     
  3. ELECTRONERD

    Senior Member

    May 26, 2009
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    Since water is conductive, you could have an oscillator with two ternimals. Stick these ternimals close to each other and when water flows it will act like a switch and turn on the oscillator thus producing a sound.
     
  4. mathew086

    Thread Starter New Member

    Aug 27, 2009
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    Hi all

    To John:
    The pipe is plastic. The objects that could come are like leaves, twigs, dust, stones, etc....mostly non-metals.
    I thought of capacitance, but then the sensing range will be of problem. The pipe is having a diameter of 11 cm.

    To Austin :
    I have considered Oscillator , but i need to detect both water and objects. Will the oscillator effective if some objects come in between the terminals?

    See the attachment. I have to sense water and objects at the red marked area.
     
  5. ELECTRONERD

    Senior Member

    May 26, 2009
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    No, it would only work for water. You could use my suggestion and then build a seperate detection unit for the objects.
     
    Last edited by a moderator: Aug 27, 2009
  6. mathew086

    Thread Starter New Member

    Aug 27, 2009
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    Hey Austin..

    If i use an oscillator, can i use the output from it to control something else? I mean .. I dont want to get some kind of sound when water flows. I want that output signal to control something... like a cleaning nozzle.( of course using a microcontroller )

    Will that be possible?
     
  7. ELECTRONERD

    Senior Member

    May 26, 2009
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    Sure, instead of having it for an oscillator you could have it going into circuit that uses a microcontroller and a motor to clean the nozzle. You can program the MCU to turn the motor CW for about 5s (I'm not sure how you'd like it) and then have it turn CCW for about 5s. After the microcontroller you'll have to have a speacial driver to power the motor.
     
  8. mathew086

    Thread Starter New Member

    Aug 27, 2009
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    View attachment 11805 Okay ... i am planning to try such a circuit....see attchamnet... the output probes goes to microcontroller... will it function>?

    Attachment modified.. the sensing probes are between the Capacitor and Resistor output is between the 1microF C
     
    Last edited: Aug 27, 2009
  9. rspuzio

    Active Member

    Jan 19, 2009
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    How about a flap held upright by a light spring. When
    the pipe is empty, the flap will stand up but, when water
    or objects flow along, they will push the flap over, which
    could close a switch.
     
  10. mathew086

    Thread Starter New Member

    Aug 27, 2009
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    Hi rspuzio

    Okay.. suppose i put up a flap. Then.lets say something like a leaf fall in through the pipe, no water.. just an object. This object will not flow like water and so it will settle just before or at the flap. Then there will be no use of it..
    The sensor has to give an output signal, when ever there is water or object. Since object cant flow, a flap would be not reliable. ( or i hope so)Am i correct?
     
  11. mik3

    Senior Member

    Feb 4, 2008
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    A capacitive proximity sensor can do the job if the permittivity of the water is much greater than the permittivity of the pipe material.
     
  12. mathew086

    Thread Starter New Member

    Aug 27, 2009
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    By permittivity , do u mean the dielectric constant of pipe and water?
     
  13. ELECTRONERD

    Senior Member

    May 26, 2009
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    Maybe he could use some IR LED's.
     
  14. jpanhalt

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    Jan 18, 2008
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    There are lots of ways to detect water per se. A problem arises when you want to detect other things suspended in or being carried by the water too.
    Since those things would be suspended in water and the OP identifies them as separate entities, then I assume he wants not only to detect water (with or without those items) but he wants to differentiate those items from water itself.

    That will be quite a bit more difficult, particularly for dust and etc.

    At this point, I think more clarification of the problem is needed. For example, do you need to differentiate dust from leaves from twigs from stones from everything else? Or, is simply knowing something is there besides pure water sufficient?

    On the subject of using an IRED, presumably one is considering an LED that emits near 940 nm. Water is reasonably transparent below 900 nm, but at around 940, the optical density (OD) per cm is about 0.1 to 0.13. That is a rough estimate based on some very old data (1920's) that popped up on a Google search. Using that number, the intensity of a collimated beam will be attenuated by a factor of 10 for every 10 cm of light path. The pipe is 11" diameter (about 28 cm), which will cause an attenuation of about 3 logs. That would be great for detecting the presence or absence of water, but would be really poor for trying to make estimates of the amount of suspended material from a change in the received intensity across the pipe. Moreover, that estimate is for a collimated beam, which a simple IR LED does not produce. If the source is not collimated, the attenuation would be even greater.

    John
     
  15. Bernard

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    Aug 7, 2008
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    Is this arrangement something to tell if rain water is flowing & clean enough to store? Is the sensing pipe virtical or horizontal, might effect resistive sensing? If trash is small, like twigs, may need a bank of IR sensors, say one per cm of diameter, or use slightly smaller pipe, depending on flow. Do you need two output s, one for water, and one for water with trash.
     
  16. mathew086

    Thread Starter New Member

    Aug 27, 2009
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    Hi all

    To Bernard:The pipe is horizontal. see attachment in the above posts.
    I just need one output, in such a way that the sensor gives output signals whenever water OR objects OR both come along.

    To jpanhalt:I do not want to differntiate between whether it is water or objects. I just need to detect that either water or object is present inside the pipe at that location. And he diameter of the pipe is 11cm and not 11"!!!!!.
    I also thought of using a IR LED and photodiode. But then if only objects( like dirt ) comes along, they will probably cover the surface of LED and stick to them. In time they may not be even removed by water flow.
     
  17. jpanhalt

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    Jan 18, 2008
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    Oops. I was thinking of a large storm drain.

    Going down the IR path, my best guess at the moment is a combination of reflected and transmitted IR emitters/detectors that are or'd. You may need more than one of each type to cover various possibilities. I would recommend the modulated type of emitter and detector to avoid false hits, but experimentation is needed to resolve that. Given an empty pipe, you could establish a baseline of "hits" for the reflected detectors. Then with objects, that number should increase. I currently use a similar method to detect movement of a 3/16" diameter steel wire at about 1 to 2" (i.e., a latch). Small twigs and dust may not reflect enough. Detection of transmitted light is primarily to detect water, but water might reflect enough so that would not be necessary.

    Here is an interesting link that I modeled my wire detector after: http://users.frii.com/dlc/robotics/projects/botproj.htm

    Scroll down to the 12C508 project. The DPRG (also mentioned in that limk) is another resource.

    Basically, the program generates the modulated IR that is needed. It then monitors false hits when the IR is off and sets a baseline number. When the IR is on, it measures the number of hits. If that number is greater than the baseline number, it registers a true hit. I would be happy to share my somewhat simplified program for a 12F5xx, if you go that direction and need it. I have had it working for several years in all levels of sunlight without problem. You could easily adapt it to account for background reflections when the IR is on and the pipe is empty too. The updating of false hits is a particularly nice wrinkle.

    I think you have some experimentation in your future. If it were me, I would play with the reflected IR first -- maybe a couple of detectors with just one emitter will work, maybe the other way around. Then, if water by itself was not detected, I would go with transmitted IR, perhaps at a different modulation frequency. This is just day dreaming.

    I think Bernard may have suggested the easiest answer, though, when he considered the question simply as trying to decide whether rain water met a minimum purity for storage based on conductivity. In that case, a simple screen or a series of screens for the big objects might work, since the rocks themselves may not effect conductivity fast enough to be avoided.

    John
     
  18. mik3

    Senior Member

    Feb 4, 2008
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    Yes. if the permittivity of the water is much greater than the permittivity of the pipe then by proper adjustment the capacitive proximity sensor will not sense the pipe but only the water flowing through the pipe.
     
  19. mathew086

    Thread Starter New Member

    Aug 27, 2009
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    oh ... tat seems quite tedious task.. i need to go through your project jpanhalt... ll let you knw if i need some help.

    Thanks...all
     
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