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Forum Index : Windmills : off topic: water level sensor
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Haxby Guru  Joined: 07/07/2008 Location: AustraliaPosts: 423 |
Hi all, Has anyone used the water level sensor from their scrap fisher and paykel electronics board? How does it work? I see it is probably a pressure sensor, but I can only see one tube going to the bottom of the tank, and there is no air pump, so I am assuming there is a one way air valve that opens when the machine is empty, then it closes and senses the pressure of the rising water? Is it 0 to 5V or on/off, any info appreciated. I was hoping to use this sensor to sense the level of the fresh water tanks in my caravan. |
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| Robb Senior Member  Joined: 01/08/2007 Location: AustraliaPosts: 221 |
If its in a on site van it may work but if you move the van air bubbles will find their way up the pipe as the water sloshes about. I found that out with a poorly designed pump system that required repriming after driving on a half full tank. I know some of those devices simply use switch contacts but am not sure about the F&P ones. |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
The sensor senses the AIR pressure in the sense tube. The water rising in the bowl increases the AIR pressure in the tube. There is no need for any valves. I doubt it would be useful for your caravan, AFAIK the thing does NOT give a varying output with the electronics on the board (tried to trace them out once), you'd need to build your own electronics. A VERY simple level sensor (for any fluid) can be made with a manometer (pressure meter)for low pressures. Just have a tube enter the top of your tank (water, sewage, whatever)and continue inside to almost to the bottom. Connect an air hose with the manometer Tee'd into it. Blow by mouth (NEVER suck) into the hose end until the air bubbles out inside the tank. The pressure shown on the manometer relates directly to the water level in the tank, you just need to calibrate the meter scale once (make a table). If you have a little valve distribution setup you can use the SAME manometer with any other tank in your caravan.  Klaus |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
The link below (warning: 200 MB .avi movie, but definitely worth it, IMHO) shows the working of the pressure switch in a washing machine, from 14:00-15:50. http://slom.1121.org/slom1/Secret%20Life%20Of%20Machines%201 04%20The%20Washing%20Machine.avi It also shows the insides of such a switch and a temporary hookup that explains the working of it. Tim Hunkins has a way of using parts for things they were never intended for. Definitely worth your time and bandwidth. Off-topic, but in my opinion the entire series should be obligatory viewing for 12-13 year old students in school. Even more off-topic... quite a few univ. students could learn a lot from that series too... better stop here before this reply becomes a rant  .
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planto Newbie  Joined: 26/11/2010 Location: New ZealandPosts: 1 |
hi, i am about to use one it appears that they are a variable inductor.....some have capacitors some don"t. I am planning on using an ne555 chip to generate a frequency and sense the changing voltage. The beauty of these is that it's not just switching and is fully variable allowing for more data gathering/set points......once the circuitry is made that is. If it all works out I will post my circuit diagram. do it then do it better! |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
I have never known of a washing machine sensor to be more than a diaphram activating a set of switch contacts. I have never checked out a F&P sensor but would expect them to be the same. With most air pressure sensors you need to have a larger tube (approx 50mm dia.) in the fluid detection area than the tube feeding to the sensor, this is to allow for a larger suface area for the fluid to act upon to creat pressure on the diaphram in the sensor. As air expands and contracts with temperture it will cause some incorrect readings. It would be far beter to use a fuel gauge sensor from a car as these are a variable resistor style sensor. In some cars they are stainless steel construction and i thing in most LPG gas tanks for cars they are all stainless. Lots of out of date gas tanks around at the wreckers, to the point you could even use the whole stainless gas cylinder as a water tank with built in level sensor. Pete. Sometimes it just works |
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