🚀 go-pugleaf

Greetings:

  The switches used to control bilge pumps typically are mercury
switches which, attached to a float, get tilted when immersed in
water.  The mercury completes the circuit, and can carry several amps
of current no problem.  You can get them for $15 to $30 depending on
the brand.  I use the "rule-a-matic" in my boat.  Be warned: they have
two problems... 1) they measure water presence indirectly (they
actually measure displacement due to buoyancy) and will only function
properly if mounted upright... 2) they tend to make intermittent
contact ("bounce" in ee terms) when jostled around even when the water
level is low (this is because the mercury sloshes around inside the
switch.)

  More fancy bilge pumps use two different techniques: 1) they spin
the bilge pump moter occasionally and measure the motor load (back emf
and current, I imagine) and shut down when the pump cavitates (runs
dry.) 2) they have an ultrasonic sensor to measure the level of the
water in the bilge.

  Water seperating fuel filters have a "water sensor" consisting of
two bare metal contacts.  A small op-amp circuit can measure the 
resistance across the two electrodes to detect water. 

  Perhaps you could be more precise in *what* you want to detect about
water? 

  By the way, what IS the "Marine Systems Engineering Lab" ?

  The Best,

      -Louis.


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............................................................................
Louis L. Whitcomb	       llw@corwin.eng.yale.edu    ph: (203) 432-4311  
Yale Robotics Laboratory	                          fx: (203) 432-7481 
Department of Electrical Engineering, 1968 Yale Station, New Haven, CT 06520