water/fuel mixture detector

[thabit ahmada]

i want to design a simple circtuit that will detect the presence water in a fuel tank.i want to use the theory of conductivity but till the moment ihave no exactly figure of water and fuel conductivity.please also assist me to get dielect costant of these two liquids.

 

[stevez]

I'd give some thought to the situation where the fuel tank was empty or nearly so. If the fuel vapors (mixed with air) are within the explosive limits you would not want whatever you are using to ignite the mixture. You will need to use very low voltage/current. There should be plenty of research information on intrinsic safety and explosive vapors.

If this is just a school project where you need not worry about such things I'd do a little more research on the conductivity of fuel. Pure water can be as high as 18 megohm/cm (I am not sure of units, it's been a while) yet water that is likely to be in the tank will be significantly more conductive.

 

[bogdanfirst]

you should use 2 contacts. apply a square wave on one and try to detect the signal on the other. use an op-amp and adjust the gain for the sensitivitiy. also, puse distilated water doesn't conduct electricity, but if it contains minerals and other stuff the conductivity varies a lot.
you should not use a continous courent for the testing probes, because of the electrolize. the coutacts will oxidate and you will find out that the circuit will not work well. i have a simple circuit that is it used just to detect water between the contacts. i'll check if it can be modified.