waterproof wire

Page 2 of 3
• posted on September 18, 2006, 1:55 pm
Matt wrote:

Important variable here is the conductivity of the water- this varies greatly depending on the concentration of electrolytes. You're assuming that the water will "short out" the resistors; if this is so, you will have 0 voltage across the supply wires regardless of water depth, provided it's non-zero. Of course, the above assumes that you're talking a bunch of resistors in parallel; if in series you still have to determine water conductivity.
Time for plan-b.
HTH, J
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 18, 2006, 4:44 pm

Unfortunately, the resisters will corrode. And they will not "short out" when water contacts them. You could use two conductors, somehow spaced equally, and measure the resistance between them, which will vary depending on the length immersed in the water.
Better - use a small tube and a pressure guage. Pressurize the tube until air comes out at the bottom. The pressure indicated on the guage will indicate the water level above the end of the tube.
Bob
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2006, 4:06 am
wrote:

Yeah, there is a wide variation in the conductivity of water, but it might be fairly constant in one place, depending onwhat else is happening there. But before trying it with resistors, I'd just put the two wires into a test water tube and see if you can actually vary the measurable resistance between the two wires by varying how deep into the water it is. You may have to raise the voltage, don't know, or maybe your voltmeter will be sensitive enough not to need that.
AFter you see if this part works you can decide what would be a useful value for resistors. It has to be more than an inch of water, otherwise "shorting out" will only lower the resistance by 1/2, but if the resistance is too high, like someone said, even a little bit of water at the bottom might basically short out all the resistors.
I guess the resistors would move on the voltage scale the range of possible voltages seen, but maybe the resistors don't really help even if they worked as you are thinking.
For spacers between the wires you can use popsicle sticks, which will last a couple years or more, or plastic sticks which will lastlonger, with two holes drilled in them, and some way to keep them from falling to the bottom.

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 18, 2006, 9:04 pm
Matt wrote:

This reveals a large enough misunderstanding of circuit theory (as well as the properties of conductors, resistors, and water) that I doubt you will be able to design this system on your own. A "storebought" solution may save you some serious angst.
Now, here's something you could probably do, which is a variation of the level-sensing switches in dishwashers. Solder a string of resistors in series. Run a conductor parallel to it which we'll call the traveller. At the junction between each resistor and the next, solder a reed switch will short the resistor junction to the traveller when a magnet is nearby. All components should be insulated from each other where necessary to eliminate unwanted shorts, of course. Encase this assembly in a tube which can be sealed against water. A magnetic float with a hole in it (like a donut) can ride up and down the tube. To eliminate "dead spots" make sure the magnet is big enough to always activate at least one switch (if you understand circuits, you'll know why it's OK for two or more switches to be closed at a time). The resistance measured between the traveller and the lead going into the first resistor will be proportional to the position of the magnetic float along the resistor "string." Use a cheap digital multimeter to measure the resistance.
%MOD%
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 18, 2006, 9:04 pm
Matt wrote:

This reveals a large enough misunderstanding of circuit theory (as well as the properties of conductors, resistors, and water) that I doubt you will be able to design this system on your own. A "storebought" solution may save you some serious angst.
Now, here's something you could probably do, which is a variation of the level-sensing switches in dishwashers. Solder a string of resistors in series. Run a conductor parallel to it which we'll call the traveller. At the junction between each resistor and the next, solder a reed switch will short the resistor junction to the traveller when a magnet is nearby. All components should be insulated from each other where necessary to eliminate unwanted shorts, of course. Encase this assembly in a tube which can be sealed against water. A magnetic float with a hole in it (like a donut) can ride up and down the tube. To eliminate "dead spots" make sure the magnet is big enough to always activate at least one switch (if you understand circuits, you'll know why it's OK for two or more switches to be closed at a time). The resistance measured between the traveller and the lead going into the first resistor will be proportional to the position of the magnetic float along the resistor "string." Use a cheap digital multimeter to measure the resistance.
%MOD%
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2006, 4:07 am

BTW you didn't say if it is distilled water, pure water, fresh water, or salt water.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2006, 4:44 am
I agree that measuring the amount of pressure required to produce a bubble would be easier but this requires a lot of power. The piezometers are remote and do not have a power source nearby. i am going to implement a sensor network to transmit the readings. the resistor method would allow me to use the power from the two AA batteries as the source for the meter. The water is ground water. Current methods of reading the meters manually are capable of 1/10 th of a foot accuracy. I believe i can improve on that. The idea of using reed switches is good and i will not have to worry about corrosion of the wire. Its just squeezing all that wiring in a tube and still allowing room for a float will be tricky in a 1/2 " ID pipe. Also keeping the tube straight for accurate measurements and not jamming the float into the pipe will be another issue. Thank you everyone for your ideas except the ones who insulted my superior intelligence.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2006, 5:24 am
Matt wrote:

if you supposedly posess "superior intelligence" why are you asking for help from the mere mortals on a newsgroup?
keep track of the time you spend on your solution & let us know the results if you get it working
this has got to be some academic MM project where time spent seems to have zero cost I hope you're not being funded with tax dollarsi in my state or fed dollars for that matter
sorry if you felt insulted but that's the price one sometimes pays for free advice from newsgroups
btw you'll get better answers if you define the problem fully from the "get go" without adding more constraints & information as the discussion unfolds
like....oh, it's got to fit......oh, it can't be......oh, i can't supply AC power.....oh, it's got to be.
cheers Bob
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2006, 6:15 am
You are right on the money Bob. this is my senior design project for college. sorry about the bad posting edicate this is my first post to a newsgroup.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 20, 2006, 12:40 am

etiquette?
They have things near my house, and all around here and on other streams, that measure the height of the stream that runs behind my house. (There has been a lot of flooding downstream, even in Baltimore-- well, a lot for Baltimore; not much for the gulf coast -- during hurricanes. I was told one of the original townhouses hear was washed away during construction, but I don't think I believe it anymore. They might have underground AC power, I don't know. In NYC there are loads of manholes that lead to power lines and phone lines, but in the suburbs I get the feeling most lead to sewers. OTOH, there are no telephone poles near my local water level meter, but plenty of aparttments and houses, so maybe that means it gets AC underground.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 20, 2006, 3:32 am
Matt wrote:

you know why I'm "right on the money"?
it's a case of experience........35+ years BTST
almost 20 years in a academic research environment (ME/CE) watching undergrad engineering students fumble along from one mistake to another.......I call it the "arrogance of intelligence" & a major lack of experience
they typically don't even know that they don't anything and spend a lot of time spinning their wheels
a little humility would serve you well in this situation
home repair is probably not the best ng to post for answer your questions.....but honestly if you had clearly defined your problem & all of the requirements of your project you would have gotten a lot of good input from this ng.
There are a lot of people here with a wide variety of skills, education & experience....more than enough to solve just about any problem
as long as its not a moving target
good luck on your project
a bit of advice......the first thing to admit is......
you don't know everything and honestly since you're still in college........you really don't know much
sorry to be so blunt but that's the way things are
a college degree (in engineering?) really just shows me that you can in fact learn that
cheers Bob
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 20, 2006, 10:06 pm

IN a big way he is to be admired for that. He didn't want to give us enought information that we could "do his homework for him".
Even though in a real design situation, you're allowed to use any help you can get. But in a leading edge design situation, there isn't that much help one can get, so I guess it's good to learn to do a lot of work oneself. ??
I really don't know what is better. Getting a lot of help here isn't the same as your parents making a paper mache erupting volcano while the kid just watches. OTOH, if you give all the facts and the right person is reading, he might answer with such a detailed description of how to do that the student is just assembling it. I don't think anyone wants that, do they?

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 21, 2006, 4:23 am
mm wrote:

mm-
Yeah....there's a fair amount of truth in what you posted but it is frustrating for guys making the replies to be getting a constant stream of "constraint updates"
that's why the best way these design projects work is a small team of students working together & an experienced older engineer to advise them.....no one does their work for them & with proper guidance they get a better result & a more valuable learning experience
left to their own devices they will typically spin their wheels, waste a lot of time, energy & \$'s, get poor outcome & have a poor learning experience.
BTST countless times
design is an iterative process but it cannot iterate correctly without proper specs, knowledge or experience
cheers Bob
cheers Bob
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 25, 2006, 3:22 pm
I have chosen to use a vibrating wire piezometer.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 26, 2006, 6:47 am
Matt wrote:

Sounds like an "off the shelf" solution.....good choice
good luck
cheers Bob
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2006, 2:43 pm

What's wrong with shining a laser down the pipe, pinging with sonar, or shoving a capped hollow tub down the thing and measuring bouyancy, or just let the pipe ride up and down and measure physical depth?
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 19, 2006, 11:35 am

Not knowing specifically what you are doing nor the conditions makes it difficult to make specific recommendations. Electricity with 2 different metals may cause corrosion. Metals that resist corrosion include gold, stainless steel, and Nichrome.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 18, 2006, 2:00 am

So far, like 8 different people have tried to help you, but unless you tell us what you are trying to do with this wire, any ideas we offer are just a shot in the dark.
aem sends...
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 18, 2006, 2:32 am

Stainless steel. Look at fishing leader. It is pretty cheap and can be fairly big. A real tackle store will have the best selection but Walmart has some
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on September 18, 2006, 1:27 pm
I doubt you'll find anything. Any kind of bare metal will corrode after awhile.
--

Christopher A. Young
You can\'t shout down a troll.