Water Level Meter

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I want to monitor the level of water in our rainwater tank
electronically - more specifically via the computer.

My thought is to hang a length of ribbon cable down the side of the
(plastic) tank with each 'core' cut shorter than the previous. I care
more about a lower level than a higher, so I figure I'll probably cut it
in something like a log curve.

Now my plan is to cross the top of every core with a resistor in series
and attach one side of the circut to the shortest core and one to the
longest. As the water climbs it 'short circuits' each progressive
resisitor, thus reducing the over-all resistance. I'd then feed this
into an A2D convertor and plug that into the computer.

+  R R R -   Water level / Resistance
| | | | |    --- / 0R
| | | |
| | | |      --- / 1R
| | |        --- / 2R
| |          --- / 3R

Does this sound sensible? Is there something obvious I've missed? What
value should R be? Should R follow the logarythmic curve so that I
attempt to get a straight line in the computer? Or am I better to leave
every R equal and (by guestimation+testing) determine a close-enough
algorithm in software?

Cheers!
Rick Measham

Re: Water Level Meter


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If you are going to build circuitry to interface to the various wires,
then you might like to llok at a project from a few years ago that did
the same thins. If think it was Silicon Chip (might have even been EA)
Used a sound pulse to measure tan level.IO was serial.

Re: Water Level Meter


Have a look at wireless Aquagauge.  Low cost, specifically designed for
rainwater tanks and available with PC interface
http://www.electrosense.com.au

Watch out for cheap "oil tank" ultrasonic units.  They are toys.

Good luck
John


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I've looked into this a few times, but then I got a bore and the rainwater
tank is full, so I haven't got around to doing anything but I've been
looking at 2 options, using pressure:
http://www.frazer.net.nz/wrting/wrtprojects.htm
Or using resistance via this circuit:
http://www.emesystems.com/smx.htm

Otherwise that Electosense stuff looks pretty good.



Re: Water Level Meter


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Water quality is a factor. Pure water is an insulator. In industry
ultrasonics is pretty much the standard. Otherwise you could use a
pressure transmitter connected to the bottom of the tank.

Friday

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Hi Rick,
             The rainwater in our tank is has quite a high resistance ,
nothing shows on the 200K range on the meter and the 2 meg. range does
strange things.
                             John Ely.



Re: Water Level Meter


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G'day John,

Thanks for that (and everyone else too!) .. your info certainly puts a
dampener on my plans for world domination. Might have to look at
something commercial :-/

Cheers!
Rick Measham

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I "sort-of" remember that EPE magazine had a design for an ultrasonic
distance measuring gizmo that could be used to measure water level -
maybe 5 or more years ago.

I tried to find something like that via their web site but did not
locate it. I did however find that the September 2006 issue features a
Water Level Gauge. My copy of that issue was still wrapped in its bag
in my pile of unread magazines. I took a peek and it uses a pressure
sensor.


Andy Wood
snipped-for-privacy@trap.ozemail.com.au

Re: Water Level Meter


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Been a long time since I tried it but the trick is probably to use an
ac source... around 1kHz should work OK.

A dc source, eg a multimeter, causes sufficient electrolysis for gas
bubbles to form on the electrodes... or so goes the theory.

I was involved in monitoring the depth of water bores at one time.
IIRC the equipment built for the job was a battery operated flip flop
and a milliammeter, in conjunction with a single pair of platinum
electrodes, which was raised and lowered by hand.  It worked fine so
long as algae and the likes didn't accumulate on the insulation
between the electrodes.  An occasional wipe with silicone helped
prevent problems.

May not work without maintenance over a long period of time though.

--
John H

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with that setup using a linear scale will probably give the best results, but
depending on how you drive the sensor, using all the same resistor may not
give a linear result.

you could get a similar result by just soldering resistors end to end for
the sensing element and just using that and the other electrode.

your device will be succeptable to ground loops if you're hooking it to
earthed PC, especially if there's an electric pump close to the tank....
so you may nees some sort of isolation somewhere.

you'll need to only run the thing for short durations else
the electrodes will corrode.

rainwater water may have an unpredictable resistance.

a capacitative sensor may work better,

Bye.
   Jasen

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