| Electronics > Projects, Designs, and Technical Stuff |
| detecting water |
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| Simon:
ok this post is part academic but if a simple solution is found I may impelment it (just to show the idiots at work what an ass we made of ourselves in choosing the supplier) Now we (my company) design and build air conditioning for vehicles, we have units that had a problem with condensation turning the air con into a shower ! so two small pumps were installed to pump out condensation from the bottom of the unit, the pumps came with sensors that go in the base so that when water is between the electrodes in the sensors the pump that has sensing electronics starts pumping the water out. Just one snag these stupid things just pump at any random time until they run dry ! and burn out due to overheating. Now I heard the guy that supplies these saying something about the circuit in the pump turning the DC to AC so assume a section of the circuit is generating pulses for another section to pick up, this now means that when one pump goes off the other one in the same unit (there is a left and right pump) also goes off, it would seem in his opinion that one pump is picking up the signal iradiated by the sensor wire of the other (like arials). Surely this is simple ? to detect water isn't it sufficient to have a DC detection method that will use the small current passed by water to say run the base of a darlington transistor so that it can then set off other circuitry ? like a mosfet ? or is there something really that tricky about picking up water. I'm going to have a play around myself - any comments welcome |
| Simon:
well I have carried out an initial test: according to my meter the resistance of water with probes about 10mm apart varies from 2 Mohms with just tips imersed down to 700 Kohms with all of the bare probes submerged, so there looks like room for being selective about the depth of water before "ignition" the other thing is though I'm using tap water, now that's not the same as ondensed water is it ? Tap water = H2O condensed = HO any ideas ? |
| Simon:
well using tap water a single 2N2222 Transistor is sufficient to get a led to light, so there we have it ! only thing is that my wire (breadboard jumper) in the water on the negative side has tiny bubbles rising from it, i suppose some sort of reaction , am I desolving my "probe" or just putting electrons into the water ? I expect to get this to work properly I would have to introduce a comparator so that I have a determined on/off at a set level of water |
| rossmoffett:
Pure water is non-conductive, it must have some salt or sediment in it to conduct. You may find that method unreliable with increasingly pure water. Typically a water detector will use two plates and check capacitance between the plates. I have a friend who designed soil moisture sensors this way. |
| Simon:
well it should be pure water as it is condensed water but from what I have seen of the units in operation there is dust/sand in the water collecting tray |
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