I need a very simple and cheap switch for water level detecting.
I need only sensing the top level of water.an electronic device is placed under water(the depth of water is about 5 to 10cm,when the water level is above the device "Switch" must switches the device on,and vice versa.
which sensor I can use?

 

Visit your local boat yard and purchase an inexpensive bilge switch.

Mark Hill

 

Depending on the application... you could use a simple cable float switch. The picture at the link is overkill... but you can buy one float only with a 30’ cable and weight. This switch will take 120V @ 5A and has no mercury. You can adjust the high and low with the position of the weight.

http://www.almegcontrols.com/cord_float.htm

Another option is a single point level switch. Again, the picture is overkill and you can order one with most any fitting or no fitting, for that matter. With SS or PVC you would need two switch points as one would cycle itself to death. A simple cube relay can be used to maintain a level.

http://www.almegcontrols.com/multi_level_large.htm

Both manuals are at:

http://www.almegcontrols.com/manual_level_control.htm

Thanks,
Bob Hogg

 

water level switch from a household clothes washing machine (cheap, adjustable and effective).

 

Look in your Grainger catalog or at Grainger.com. They have inexpensive float switches.

Or you can try gems sensors.