# How do you build a water level sensor

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#### raeqwon

I'm working on a project where i need some kind of level to indicate how much water i have in the tank. I have done some research on the net to find such a sensor, but all the ones i have found are very expensive and i need to build this sensor from scratch. can anybody give me some hints or schematic i can look at to design this?

Thanks

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#### Walt G

Many ways to make a sensor, depends on high / low limit sensor or constant level sensing. The simplest constant level may be to take a float, connect to arm, connect to potentiometer with small voltage and measure wiper.

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#### Bob Hogg

Hi You may get some ideas from the web sight:
"http://www.almegcontrols.com":http://www.almegcontrols.com
For low cost I would suggest a simple plastic model located in - products - level sensors - single point. You could then attach a rod to it a stick it in the tank to any level. Continuous model - it would be cheaper to buy one - than
make one. If you want to buy section parts to make or assemble a multi point unit - email a request. Email Almeg for a quote. Thanks Bob Hogg

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#### Grumby

Expensive is relative. If this is an industrial project you're better off to bite the bullet and buy one rather than construct one, you'll save youself some hassle and money down the road. If however this is a school/home/farm project there are a number of cheap alternatives.

Remember that when it comes to CHEAP -vs- GOOD -vs- FAST, you can have any two, but never all three. Cheap and fast won't be good, good and fast won't be cheap, cheap and good won't be fast.

1) Use load cells to weigh the tank. If the tank is symmetrical and evenly distributed on its supports, you can get a reasonable approximation with just one load cell under one support and multiply the result by the number of supports. Accuracy can be improved by calibrating the load cell output to the actual level as measured with a dip stick or other simple device. Inexpensive

2) Mount a multiturn potentiometer with a tooth belt pulley on it at the tank top. Using a long tooth belt cut in half, attach one end to a float and the other to a counterweight that hangs ouside the tank. You will have to tinker with the counterweight so that is just balances the float. If your tank is very turbulent this is going to be a troublesome approach, but for a calm tank its cheap if not a bit kludgey. You can also use the counterweight as a pointer to a (inverted) visual scale on the tank exterior.

3) Use your imagination and create a float/slidewire/variable resistor that fits your tank. Remember that with counterbalancing weights or springs you can put the resistor almost anywhere outside the tank. Get creative.

4) If you happen to have a low pressure transducer you can just measure the fluid pressure at the bottom of the tank and calibrate that to level. Good pressure transducers can be obtained for $200 and up. 5) If you only need point level, you can get float switches from "grainger.com":http://www.grainger.com or "omega.com":http://www.omega.com for about$15.00 each.

6) Extend two parallel conductor rods into the tank from the top to bottom. The resistance will change with the ammount of rod sumberged in the water. Make sure the rods are insulated from the tank if it is metallic. Its cheap but its also quite finiky and subject to changes in your water (dissolved minerals, etc) and doesn't offer much resoultion without expensive electronics.
LOW VOLTAGE ONLY!!!!

7) How cheap do you want to go? Is this a high school project where you want to impress an easily impressed teacher? Is your tank fairly small? If so, look up LVDTs on the net and see how they are constructed. You can make a crude one with a piece of thin wall PVC pipe, an iron rod, and some varnished copper wire. Attach the rod to a float large enough to support the rod. The electronics are failry simple and you can find this info on the net. This approach has a high "cool factor" for a school project, but I wouldn't recommend it anywhere else, unless you already have an industrial LVDT, but your range of change in level will be somewhat limited.

8) You can take a temposonics transducer and mount the magnet to a dough-nut float. A bit more expensive, but a very good fluid level measurement method for a few hundred dollars.

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#### Curt Wuollet

I found many varieties at good pricing (compared to some well known vendors) in a Digikey catalog from Measurement Specialties amd SenSym ICT,
They include diaphragm isolated types and the whole nine yards. Bare sensors or with signal processing.

"http://www.digikey.com":http://www.digikey.com

Regards

cww

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#### Anonymous

Let me know more about transistor arrangement.