In this post we learn how to make anti-corrosion probes for water level sensor and controller circuits by using alternating supply across the probes.
How it Works
Let's understand the concept used behind the designing of this anti-corrosion probe circuit for water level sensors and controllers.
Corrosion in water level sensor probes take place due to DC supply which is normally used for triggering the probes through water. This is aggravated by the process of minor electrolysis across the probe terminals which in the long term usage results in formation of layers of chemicals an minerals, gradually inhibiting efficient working of the probes and affecting the water sensing ability of the circuit.
To remedy this an AC supply is recommended so that the process of electrolysis is unable to develop across the probes due to the constant flipping of the supply polarity across the probes through the alternating nature of the supply.
In the design presented above, the AC supply is derived from a 12V transformer, via a couple of high value resistors for dropping the current across the probes.
The supply is carried forward to the inputs of an "OR" gate which specifically deals with this AC and produces the relevant output depending on whether water is present across the probes or not.
In the absence of water the applied AC generates alternately changing potentials across the two input pins of the OR gate. As per the truth table of the OR gate, a 0 and 1 or 1 and 0 on its inputs correspondingly creates an output of logic 1. This implies that while the alternate switching is applied over the two inputs of the OR gate, causes its output to consistently be at a logic 1.
Now if water happens to bridge the probe points, it instantly causes a relative short across the points causing the AC to disappear at the inputs of the OR gate.
In this situation both the inputs of the OR gate is held at logic 0, which causes its output to revert from logic 1 to a logic 0.
The above action switches ON the PNP transistor enabling the output to trigger the intended load such as a relay or an LED.
More number of gates could be employed with parallel probes points at different depths of the water tank in order to sense the various levels of the water if required, for building a multi water level anti-corrosion sensor probe circuit
The OR gate IC could be a IC 4071 or any other similar.
Simple Corrosion Free Water Level Sensor Circuit
The following figure a possible simpler method of creating a corrosion free water level sensing terminals.
In the diagram we can see that the reference ground terminal at the bottom of the tank is supplied with an alternating +/- 6V instead of a normal DC. This forces the other terminals to conduct in a push-pull manner with the reference to this base terminal and this hopefully prevent corrosion from developing across the connected water level sensing terminals.
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Godson says
Hello sir Swagatam,
I stumbled upon this link in the response you gave to a question of the main article. I assembled the the circuit in the main article and it worked quite well. But I assembled and tested it in a small water container. Thank you for providing the circuit above to solve the issue of corrosion. I want to wire the last circuit with just four levels and not six. My questions go thus:
1. Can I use the circuit in a water tank that is about 3-4meters in height and get a good result, knowing that the distance between the probes will be much? If yes,
2. Do I put the “base probe” which is from the BC547 and BC557 at the base of the tank and put the other four probes at their respective positions or will each of the four probes have their own “base probe” beside them for better response?
3. Is the IC still 4049 or another?
Swag says
Hi Godson, glad you could build it successfully.
here are the answers:
1) yes you can use ti for deeper tanks since the use of a frequency makes the conduction sharper and long ranged.
2) You mean to say the emitter probes? Yes the probe is required to be placed at the bottom of the tank
3) The IC is 4049.
Godson says
Hello sir Swagatam,
Thanks a lot for the response. Yes I meant to say the emitter probes.
I have more questions from the second schematic above:
1. The 2M2 resistors are not connected to the positive rail of the supply as against what is in the main article. Is that an omission?
2. The center-tap of the transfo is connected to the ground. Is it the same ground that is supplying the 4049?
3. Can a 12-0-12 transfo be used in place of the 6-0-6 transfo?
Swag says
Hi Godson,
thanks for pointing out the mistake.
1) the 2M2 resistors must be connected with the positive supply, it has been mistakenly missed
2) yes the center tap ground is common for the IC negative terminal, and the rest of the circuit where ground symbols are indicated.
3) 12-0-12 transformer can be used
Peter Bestbier says
Hi Swagatam
Just a short note to convey my appreciation for the effort that you put into your very enlightening articles.
As a semi-retired mechanical engineer, I have really benefited from your excellent articles and have as a result, successfully built several practical circuits. I look forward to building many more once I retire.
Many thanks
Kind regards
Peter Bestbier (Cape Town South Africa)
Swag says
Thank you Peter, The pleasure is all mine!! keep up the good work.
Shry says
Dear sir,
I have simply used electronic bell (3V Dc supply) inputs as water level sensor inputs & a switch in series (used when borewell is on).
It worked well for some months but now its not giving proper alarm on tank being full.
i have changed batteries as well as filed the tips of copper wires used as probes but problem persists randomly.
what could be possible fault.
Swagatam says
Dear Shry,
how did you place the probes? make sure the distance between the probes is minimum, may be around an inch apart, now place this set of probes at the brim of the tank for sensing and check the response…
abubakar bakar says
SIR ..if water reaches at prob and stil water is there transformer will not got dammage??
2ndly is or gate ic read the ac signal …morever its a digital ic? so how is it possible??
Swagatam says
Hi Abubakar,
transformer will not get damaged because the transformer is not near the water, only its output is immersed in water that too through 2M2 resistors.
An AC is made up of two alternating DCs, right?, therefore applying this AC will be like applying two alternating DCs at the gate inputs….therefore the working will be perfectly OK just as explained in the article…