which is a good metal to use for probes in water?

Discussion in 'General Science' started by zirconx, Mar 18, 2010.

  1. zirconx

    Thread Starter New Member

    Mar 10, 2010
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    I'm making a water detector. This will be used to monitor water in my sump pump discharge pipe, so it will be seeing water every 10 minutes or so. I need something stiff that I can insert into a threaded cap that I will be attaching to a "T" on my PVC piping.

    My first thought was to use 14g copper ground wire from some romex I have. Its stiff enough. But then read that copper oxides in the presence of moisture. Would this oxidization prohibit the conductivity?

    I also thought about using aluminum, I went to the hardware store and they have aluminum rod but its not thin enough, I would like something no larger than 12g in diameter, although 10g might work too.

    I think I can get small brass rod at the hobby store, I've seen it there before but wasn't really looking closely. They might have aluminum too.

    Any suggestions?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    The crud on copper shouldn't be much of a problem. Brass is an alloy of copper, so no improvement.

    Aluminum doesn't corrode due to an oxide film, which is not real conductive.

    Copper would probably work, but you can always use stainless wire (fishing leader). SS doesn't take solder, though. You would have to use a crimp connector.
     
  3. Wendy

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    Mar 24, 2008
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    Stainless gets my vote, but there will be a reaction where dissimilar metals touch. Over time it will be eaten away. I don't know how I'd handle that one, unless you stick with copper.

    If you can put the connectors where you can reach them easily, I suspect it will need service now and again.
     
  4. iulian28ti

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    Dec 4, 2009
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    Gold maybe...?
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Stainless will take solder. Have you tried with the proper flux?

    Stainless would still get my vote, #2 is copper. Of course, you could also consider gold. Solders well, doesn't corrode, is malleable, good conduction. What's there to lose? ;)
     
  6. beenthere

    Retired Moderator

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    Obviously not. The solder never seemed to wet the surface.
     
  7. jpanhalt

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    Jan 18, 2008
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    I use an old bottle of "General Purpose" acid flux (http://www.laco.com/productDetail52.aspx). It contains HCl and better ones are probably available today. But I bought a lifetime supply, which is the smallest amount I could buy. Here is a picture of a contact sensor made with 316SS. I soldered a small brass sleeve to the SS, then soldered the wire to that using rosin core solder. I didn't want the acid in the stranded wire.
    [​IMG]
    John
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Looks like Ersin Multicore needs some help.

    Re the acid - I was loking over an older house once and saw where the owner had added some Romex to the original knot and tube wiring. Just ripped off some of the woven insulation and took a turn with the Romex. Then he used acid core to make the joint - it had grown to a ball of white corrosion.

    Gave that house a pass.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    You think that is bad. Here is what some DIY'er had as a fire alarm:
    [​IMG]

    Now, back on topic. Stainless is a good option, but so is copper.

    John
     
  10. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    Stainless steel, and use only short measurement pulses or alternate the polarity.

    If you put DC across the electrodes, you will electrolyse the water and cause corrosion.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Rather than having bare metal exposed to water, I'd make an air capacitor out of a couple of parallel metal plates, and coat them with a waterproof material.

    Then use the plates as the "C" in an RC oscillator.

    Water has a dielectric constant of around 78, while air has a dielectric constant of approximately 1. If the two parallel plates are separated by water, they will have roughly 78 times the capacitance as when separated by air. The oscillator will therefore run far more slowly when the plates are immersed than when they are in air.

    Then it is a matter of determining the frequency of the oscillator. This could be a simple "missing pulse" detector.
     
    Last edited: Apr 2, 2010
  12. Ghar

    Active Member

    Mar 8, 2010
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    That's a pretty good idea Wookie, I'll try to remember to try that someday...
    Though maybe a capacitive divider might be easier? I guess it would depend on what kind of capacitances you get.
     
  13. retched

    AAC Fanatic!

    Dec 5, 2009
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    I think he meant to say water has a dielectric constant around 78 and air around 1.

    And, a good idea.
     
  14. SgtWookie

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    Jul 17, 2007
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    Yes, thanks for the catch, Retched. Post has been corrected.
     
  15. PRS

    Well-Known Member

    Aug 24, 2008
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    If price is no object I vote for silver.
     
  16. Wendy

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    Mar 24, 2008
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    Silver is very reactive as metals go. If price were no object platinum or gold. I liked Wookie's idea best though, a no contact sensor.
     
  17. rvh002@gmail.com

    Active Member

    May 15, 2009
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    Forget about any fancy metals or ideas, stailess steel is used, and has been used for many years in this kind of project and a standard unit with various options can be bought from your local agent of Yelland products. (or similar)
     
  18. mik3

    Senior Member

    Feb 4, 2008
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    I would go with SGTWookie's idea because it is the most reliable and it does not cause electrolysis like probes.
     
  19. Tate

    New Member

    Mar 8, 2010
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    If you do decide to use a stainless steel probe, go to you local welding supply shop. Ask them for SS tig filler material. If they are any good they will have a couple sizes and grades.
     
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