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Liquid level sensors often use two probes, when the resistance between those two probes changes with reference to the level of the liquid between them, that change is resistance is read as change in Volume. Now my understanding was the the current to these two probes needs to be AC so ionic migration does not cause havoc to the experiment. But the below circuit I found uses on DC current. Is this circuit right? If yes, how does this work?

Liquid Level Sensor

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2 Answers 2

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The circuit is a simple water level sensor that works on DC.

When probes touch water with ions, small current can pass through water to transistor which turns on. Water is used as kind of resistance.

There will be about 2.5V between probes so DC current may cause problems such as ionic migration.

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    \$\begingroup\$ Yes, and that ionic migration would for sure cause drop in voltage and unreliable readings. How would you say this objective can be achieved through AC? \$\endgroup\$
    – John Snow
    Commented Nov 3, 2023 at 8:07
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You should use something like this, working as AC sensor (could be simplified).
C5 is the variable capacitor. Can be also a resistor.

enter image description here

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