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

Thread Starter

zirconx

Joined Mar 10, 2010
171
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?
 

beenthere

Joined Apr 20, 2004
15,819
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.
 

Wendy

Joined Mar 24, 2008
23,415
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.
 

jpanhalt

Joined Jan 18, 2008
11,087
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? ;)
 

jpanhalt

Joined Jan 18, 2008
11,087
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.

John
 

beenthere

Joined Apr 20, 2004
15,819
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.
 

jpanhalt

Joined Jan 18, 2008
11,087
You think that is bad. Here is what some DIY'er had as a fire alarm:


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

John
 

rjenkins

Joined Nov 6, 2005
1,013
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.
 

SgtWookie

Joined Jul 17, 2007
22,230
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.
 
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Ghar

Joined Mar 8, 2010
655
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.
 

retched

Joined Dec 5, 2009
5,207
Air has a dielectric constant of around 78, while air has a dielectric constant of approximately 1.
I think he meant to say water has a dielectric constant around 78 and air around 1.

And, a good idea.
 

Wendy

Joined Mar 24, 2008
23,415
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.
 
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)
 

mik3

Joined Feb 4, 2008
4,843
I would go with SGTWookie's idea because it is the most reliable and it does not cause electrolysis like probes.
 

Tate

Joined Mar 8, 2010
11
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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