Measuring water pressure in an open tank

[vasco_990]

Hello to everyone...

I've been reading these blog and searching the web trying to find a solution for my problem, but I couldn't find anything.

I need to meassure the water pressure (differential pressure) in an open tank.
The colum of water is aprox. 10-15cm tall.
I need to do these at all times, with an electronic sensor with any sort of analoge output (voltage, current). Also I need a sensor with a precission of about 2mm.

Can anyone help me with the sensor model an connection?... how does it meassure the pressure?... you sink it in the water or you do it with a air column?... if it so, you have to take in consideration water condensation?...

Thanks in advance!... and sorry for the bad english.. its not my native languaje...

 

[vasco_990]

I've searched pages like farnell... but i can´t find anyting that suits my needs... most of the sensor are for gases... not water... and i don't know if measuring a water column could cause condensation to break the sensor...

 

[Danger]

Welcome to PF, Vasco. Your English is admirable.
I'm uneducated, but like to mess about with stuff like this. It seems to me that one of the easiest approaches would be to put a piezoelectric transducer in the bottom of the tank. That would be a simple measurement of the weight of the water column above it.

 

[vasco_990]

te problem is that the sensor needs to measure between 0-10mBar (0-10cm H20) and ai can't find a piezoelectric transducter that measures that...

 

[Danger]

Hmmm...
What about perhaps some sort of deformable bladder (like a balloon), which could transfer an air pressure signal via tubing to an analogue gauge?

edit: I just thought of a couple of things that eluded me before. First, won't the water pressure change according to the surrounding barometric pressure? If so, is it a problem? Is that what you meant by "differential pressure", and if so wouldn't you have to have a barometric off-set to your water pressure gauge?
My other thought is that you didn't mention the area of your tank. I might be mistaken about this, but it seems to me that having a large "footprint" for your measuring device should increase the sensitivity. (What I mean is that 5mBar on .5 m² should be easier to decode than the same pressure on .05 m².)

 

[brewnog]

If you can't find a piezo pressure transducer you're not looking hard enough.

 

[fleebell]

Try looking up auto float type gas tank senders. That will give you an analog output that should be sensitive enough to work with.