detecting water

[Zero999]

I have another idea involving capacitive detection.

Build a similar circuit to the one I posted previously but rather than using discrete capacitors, use two large metal plates coated in an insulating material, such as two planes on a PCB with solder resist on top.This has the advantage of not having any exposed metal electrodes to get corroded by chemicals. You could use a double sided PCB, one side for the water sensor, the other for all the components which will be potted.

[Simon]

so if the electrode are coated they will still act as a capacitor ? that would be very good as it would eliminate the waters resistance from the equation. discussions about how to solve the particular problem my company has are academic as they are not officially looking to me for a solution and are thinking of having the water drain out of the sump into something like a car screenwash bottle with a pump in that, of course they still have to get that pump to detect water, the engineer told me to keep my ideas handy as they may need some input later. at the end of the day I could design the thing and the idiot supplier could make it for us. So the game is still a-foot even if for my personal satisfaction of getting it to work

[Zero999]

It still relies on the conductivity of water, it's just that the solder resist and PCB ground plane is acting as a capacitor.

However, I think water has a higher dielectric constant than air anyway so the capacitance should increase slightly even if the water isn't conductive.

I think you need to perform some experiments to find out for sure but I'm sure it's possible.

[MoJo]

A little more info would be nice, as to what type of pump and what is its sensor? I think building another sensing mechanism when this should already contain one is not the right approach. It would be better to spend energy troubleshooting the current setup. Is the pumps sensor false triggering, or is it missing a comparator component that tells it the off state compared to the on state (what the PIC should be doing in this case, a voltage comparator would be better).

I think the motors built in sensor is a pressure sensor, or it needs a pressure sensor to complete it (again more info would be great).

Read up on Liquid Level Detecting, might be of interest to you

http://www.freescale.com/files/sensors/doc/app_note/AN1516.pdf

I'm a student going into the Biomedical field, (Medical equipment meets Electronics Engineering), we primarily always discuss the significance of sensors and sensor design. Another alternate approach which probably is simple but I would rank second after the above mentioned setup is to create a displacement based sensor, in this case a capacitive sensor. Having a top floating conductive material and an anchored bottom material you create a capacitor with changing distance of plates. This can be used to set a lower bound threshold that is checked every 10 minutes ... if it isn't met, than the pumps are turned on ... they only turn off when that threshold is met again.

Hope it helps,

EDIT: Oish, I should of read Hero999's post more clearly. He mentions exactly what I just repeated like an echo ... but nonetheless a good idea still.

[Simon]

the pumps are reciprocal and are housed in a small plastic case along with the custom build circuitry and the sensor is in the sump. so far many ideas have already been tried to improve the current setup but it is now clear to us that the whole design is garbage and does not match what the supplier is telling us. Many have said in the workplace that a float sensor should have been used in the first place but as always with management and design the wrong people make the decisions. I think our engineer not having any real knowledge of electronics (although not wanting to admit it to the point he carries an oscilloscope he does not know how to use) and has trusted the supplier who seemed quite reputable and acustomed to these sorts of military projects. It is now chear that it is all garbage.

My intent was to see if there are better methods of doing this, I came up with a similar circuit myself to the suplier but one that worked ! however as has been pointed out a capacitive sensor is best. How will a pressure sensor cope in a moving hehicle over rough terrain ? the ide is that this thing will be tipped all over the place.

your pressure sensor looks interesting but having looked at your link a bit it says that the output is a very low voltage that needs amplifing, we already have an issue with interfearance i think the sensor output may be drowned in the surrounding EMI