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I'm trying to make a water level indicator. I don’t like giant float switches. If anyhow change of inductance can be measured due to change of water level, it would be helpful.

I'll buy copper coil tomorrow.

Peter Mortensen
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Sadat Rafi
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  • https://www.allaboutcircuits.com/tools/coil-inductance-calculator/ Just plug the values in. – Eugene Sh. Dec 10 '20 at 21:40
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    Compare the relative permanently of vacuum (air) and cater and you’ll quickly find out why water solid state level detectors are either resistive or capacitive. – winny Dec 10 '20 at 21:41

2 Answers2

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Practically none at all.

On the other hand, capacitance will increase thanks to the relative permittivity of water, so if the inductor is part of an LC oscillator (self-resonant, using its self capacitance, or with a very small C) you may see a useful change in frequency.

  • As Brian says in this answer, capacitive is going to be much better than indictive. Instead of using an RC oscillator, you could also measure the capacitance directly with a capacitance-to-digital converter such as AD774x series or FDC100x series. – Jack B Dec 11 '20 at 10:37
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    I have already tested that. There’s almost 0.2 uF difference is created. – Sadat Rafi Dec 11 '20 at 12:14
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    0.2uF seems suspiciously high. I'd have expected something closer to 0.2 nF : still perfectly easy to measure. Unless your coil is absolutely enormous, this makes me wonder what else (conductive liquid? how are you measuring?) might be going on. –  Dec 11 '20 at 14:02
  • I turned two coils ( like parallel plate capacitor) and dipped it in water. Measured the capacitance using my multimeter. – Sadat Rafi Dec 12 '20 at 14:00
  • Were they insulated from the water? If not, you were probably (=almost certainly) measuring conductivity. –  Dec 12 '20 at 14:11
  • I'll check again later. – Sadat Rafi Dec 12 '20 at 14:37
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The relative permeability (electromagnetism) of water is so close to air that you would not get any significant difference in inductance for your your coil.

RoyC
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  • Thanks. I think somehow I have to move iron through coil. – Sadat Rafi Dec 10 '20 at 21:52
  • Try a resistive detector. Put two metal conductors into the water and measure the resistance between them with a multimeter. Raise and lower the water level and see how the resistance varies to get an idea for the range you must detect. To make the circuit to measure the water level without your multimeter, drive current between the two conductors in the water and use an op-amp to amplify the voltage difference between the conductors, giving you an analog voltage inversely proportional to the water height. – Zane Kaminski Dec 10 '20 at 21:58
  • This will work if the purity of the water remains constant. – RoyC Dec 10 '20 at 22:01
  • Only issue is that various minerals and impurities in the water will affect the resistance dramatically, so you must use the same water. Edit: yes, what RoyC said. – Zane Kaminski Dec 10 '20 at 22:01
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    It starts electrolysis. – Sadat Rafi Dec 10 '20 at 22:37
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    If you are measuring the resistance of water, consider using an AC (or squarewave DC). This will reduce electrolysis of water, and the subsequent corrosion of the electrodes – CSM Dec 11 '20 at 10:22
  • (Double *"your"*.) – Peter Mortensen Dec 11 '20 at 17:30
  • How about some actual numbers? – Peter Mortensen Dec 11 '20 at 17:30
  • @Peter Mortensen To 5 decimal places how about 1 and 1. – RoyC Dec 11 '20 at 18:13