How does this water level sensor works ?

[Externet]

Hi.
The sensor here is in the 'arch', about a 1watt resistor size, connects to the guts of the device to turn it off if not submerged in water.

**broken link removed**

It is an ultrasonic fogger unit as in here:

**broken link removed**

 

[Sceadwian]

It could be a mechanical pressure switch where there's a small sealed bubble in the tube and when the water pressure squishes it it closes a relay contact. But it looks a little more like it could be an inductive sensor as well. You'd really have to take it apart or ask the company that makes them.

 

[spuffock]

water doesn't change the inductance enough to be easy to detect. It's got to be capacitive.

 

[Sceadwian]

They can spuffock, I've used plenty of conductance sensors that are used to control chemical concentrations in water tanks. They go off limit low when they're removed from the water. They're usually donut shaped but I wouldn't see why a solenoid wouldn't work as well.

Capactance is a possibility but based on the shape of the sensor that seems a bit out of place, in order to change the capacitance there would need to be a gap between two plates, that's a straight tube.

It's really hard to say there's just too many things this could be, unless someone is familiar with it in particular.

 

[spuffock]

sorry I thought you said INductance.

 

[Sceadwian]

It's a bit of a misnomer, as the probe's are inductors but it's more complicated than that. I somehow doubt this is one of those types though as they're far more sophisticated than simple water detection. There's just too many things it could be to tell what it really is without dissecting it, and it looks relatively well sealed.

 

[Mr RB]

Maybe it's a resistor or thermistor? If some power is put through it it will be hot and higher resistance when NOT submerged in the water.

The fogger probably has a microcontroller in it so it's trivial to use the ADC to check the resistance of the sensor resistor.

 

[KeepItSimpleStupid]

I'd go with the thermister/resistor. You apply a certain amount of power to the thermister/resistor and if it is cooled the value will be a lot different than if it is in air.

This method is used for low fuel in a car gas tank.

 

[Externet]

I have my doubts about being thermistor related.
The unit does not energize submerged in gasoline; but does in water. I have one, tested and confirmed.

 

[Sceadwian]

This method is used for low fuel in a car gas tank.

Say WHAT? An intentional heater in a cars gas tank?


Externet, you submerged one of these things in gasoline to test it? I'm not sure if I'm afraid of that fact or if I admire it micronized gasoline particles is a terribly dangerous thing! Even the military fuel air bombs at best disperse it as a fine mist.

That however make it being a mechanical switch a bit unlikely. Gasoline makes a better dielectric than water so I think that makes the capacitance thought less likely as well. I'm still leaning towards inductive simply because atomizers like this work at about 1.7mhz and having that clock (with power available) already make shunting a little of that power to an inductive sensor more practical, but the sensor size doesn't make sense as it hints at it being a solenoidal inductor which rules out induction because that would turn it into an RF source.

We're all shooting in the dark though, if you really want to know the only way to find out for sure is a very careful dissection. Unless someone else that reads this posts can provide a more likely alternative.

 

[Mr RB]

I have my doubts about being thermistor related.
The unit does not energize submerged in gasoline; but does in water. I have one, tested and confirmed.

Very interesting! Well then it might be an actual water sensor, the black matte coating looks similar to the black coated humidity sensors in VCRs.

From what I know they are a resistive device that changes resistance based on water (humidity). And they do tend to fail over a long time of use so there's probably some chemical process involved.