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Topic: Water/flood sensor? (Read 31138 times) previous topic - next topic

Doug101

I have a basement with a sump pump mounted two feet below the floor in a tube.  I'm looking for a way to detect if the water level has risen above a certain level.  (Sump pump isn't working).

Seems to me water sensor get corroded over time and become unreliable.  So I think that leaves an ultrasonic sensor to measure the water level or simple float switches?

Is one better/more reliable than the other?   

MarkT

In a damp environment any sensor you use must be hermetically sealed anyway, whatever type it is, unless
you can bring the electrical part of it out to a ventilated area.

I suspect its quite important the sensor you pick will fail, if it fails, by falsely indicating flood, so electrodes
in a protective open tube might be good - any kind of damp and you'll tend to get leakage current, but you'd never see a completely open circuit with two wet electrodes.  No moving parts to sieze up, and using it is simple, just
apply 5V through a 100k series resistor and measure the voltage across the resistor (in effect
the current through the resistor by proxy), and threshold.  Remove the voltage when not actively
measuring to prevent electrolytic action.  A capacitor across the resistor can remove any ac or RF pickup
signal.

You can test the thing easily in situ (using a cup of water).
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wildbill

I'd be inclined to get something designed for the job - bilge pump float switch.

wvmarle

+1 for a float switch.

Hermetically closed; usually based on a fixed reed tube with magnet attached to a float. Water level rises, float is pushed up, magnet closes the switch (or opens it, depending on the design).
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MarkT

I'd be inclined to get something designed for the job - bilge pump float switch.
Slightly different job I think - the one thing you want from a flood detector is reliability after
years/decades of time without any maintenance or even any regular testing - you can put up
with occasional false positives, but a false negative is extremely bad.   Anything mechanical
is subject to build up of dirt, corrosion, rodents, you name it.

I cannot imagine a situation where two metal electrodes will fail to conduct submerged in water,
however badly corroded, gummed up with crud, infested with insects/rodents.  Seems pretty
failsafe, the wires connecting them are then the reliability issue, not the sensor.

In fact a conductivity sensor is quite likely to give false positives when dirt or corrosion or whatever
affects it, so it will self-diagnose deterioration.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Doug101

Interesting discussion....  The problem I see with exposed electrodes in the build up of minerals and electrolysis of the electrodes.  This is rain/ground water and on the plastic bub there are mineral deposits.   I had a bilge pump switch.  This is a mechanical switch, and for some crazy reason it turned into a resistive load.  Maybe water got into the switch mechanism.  Anyway it failed.  I'm inclined to go with the float with a magnet and reed switch type,

Looking for longevity.  Maybe what I will do is use two or three so if one fails I have some redundancy.

wvmarle

MarkT (#4) has a point when it comes to reliability as this is a float switch that in an ideal world would never be triggered. That is a potential issue for reliability, as it being triggered regularly means you're basically testing it regularly, and a float switch is a mechanical thing that can get stuck when not used for a very long time.

For probes, safest to go for copper. Pretty resistant to corrosion, and at least it's the same metal as your wires so no galvanic corrosion issues combinations of metals are prone to. Place them close together in free air, and make your sensing quite sensitive: this way you would start to sense conduction from wet spiderwebs in between (a false positive once or twice a year is not that bad, it prompts you to clean the thing). Maybe a 100k pull-up resistor and using an analog input (so even if you have a 1M resistance between the probes you can easily sense it - you don't need instant reaction anyway).
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Nick_Pyner

Slightly different job I think - the one thing you want from a flood detector is reliability
Sounds like the description for a bilge-pump switch to me. The only "difference in the job" is that, if the switch fails, the ship sinks.

Doug101

In my case the basement flood.  We had rain yesterday and the pump (which I just purchased 3 years) failed.  Had almost 2 feet of water in my basement swimming pool.

The pump before that failed not because of the pump, but the float switch.  I opened it up to find one of the caps had exploded.









wvmarle

Makes me wonder what kind of high-tech float switch you had that it includes capacitors.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Nick_Pyner

I'm afraid I don't understand that. I understand our bilge-pump switch is nothing more than a magnet and a reed, no caps, and it just needs occasional checking that the arm moves. Don't ask how old it is, but ti works just like it is supposed to. You can get these little float switches for about a dollar on eBay. A float donut slides up a shaft, again magnet and reed - all well-sealed. They come in a variety of styles and lengths. Buy two and install in parallel.

Doug101

The bilge pump switch I had used a snap action micro switch.

I'll post some pictures of the sump pump switch so you can see the cap.  There's a relay in there too.  And all of this can be under water.

sibin_lal

float switches would be more reliable i guess compared to the HC-SRO4 . if you really want an ultrasonic sensor then water proof the PCB area or else go for a sealed unit .

i use both float (upper and lower cut off) and ultrasonic (water level ).

wvmarle

Advantage of the ultrasound sensor is that it's actively used all the time so you can detect when it's broken (it's not likely to last very long in such an environment, unless you get a waterproof version).
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Doug101

A cup of water is a false test.  As mentioned previously this is rain water which has passed through dirt so I;m sure it's full of anions such as Calcium, Iron, Mangneese and other ions.  Only way  could test would be to have the electrodes sitting in the muddy water for a year or two to see how corroded they will beome.  If electrodes were to be used isn't there a current always passing between the two electrodes?  Seems to me a little electroplating would be going on.

For less than $5.00 I can get a stainless steel float.  And for less than $7.00 I can get a double stainless steel float.

https://m.banggood.com/50W-220V-Stainless-Steel-Vertical-Liquid-Water-Level-Sensor-Tank-Pool-Internal-Floating-Switch-p-1031163.html?rmmds=detail-bottom-alsolike

https://m.banggood.com/200mm-Liquid-Float-Switch-Water-Level-Sensor-Stainless-Steel-Double-Ball-p-1009563.html?rmmds=search

I just think this would be far more reliable than a electrodes or a bilge pump switch.

And since no one has mentioned a ultrasonce sensor I guess I won't persue that.

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