Boat Forum / Electronics / July 2008

Plug it into a sonar unit, put it in the water and see if you can see the
bottom in a hundred meters of water would be best.....

I was trying to test his transducer and cable out from the easy end to
get to without swimming in bilgewater.  If the voltage rises from the
piezoelectric effect of the transducer listening to the noises in the
water, it's probably 99% just fine.  If no DC ever shows up, cable or
transducer is bad, not the control head/transmitter/receiver....probably.  
He didn't say he had a neighbor to swap units with to test it.

The tiny transducers on pleasure boats don't need a kill warning tag on
them.  The transducers in a nuclear sub, to give you a perspective are
each about 20cm in diameter and 1.4 meters long.  There are hundreds of
these in an electronically scanned array fore/aft/up/down/beamwise

It's no fun scrunched up in the sonar dome testing the damned things with
the test set, either....no air, hot as hell, cramped tiny space, no place
for your legs and feet.  Been there....done that....it sucks.

What's fun is when the old transducers are sitting face down on a pallet
waiting disposal.  Take a screwdriver and short them out quickly you get
a real impressive POP!....(c;  "Hey!  Why did you guys leave these things
ON?!", you ask the newbie who jumped.

The effect is the same as the spark igniter on a new gas grille.  You
bang on the transducer, you get a high voltage spike from the
piezoelectric crystal.  There's not much current unless the crystal is
huge and the circuit is very high impedance...high voltage.

I'm sure the manufacturers would rather you just bought a new one.  Not
sure what they'd "recommend" to test.  Most problems I've ever seen are
caused by the cable rotting off them.

If the transducer is mounted in the hull, there should be enough noise
going by it to make some signal you could see on an oscope and you can
probably see some DC voltage if nothing is leaking....which would be
unusual in a bilge, I'm afraid.

Measure DC volts with an autoranging Digital voltmeter (They're 10M ohms
impedance) and if you get no reading, switch to ohms and hope it reads
infinity (open circuit), which is what the crystals are.  Plug in a
scope and see if you see any noise at the crystal frequency, which is
too high to hear, of course.  If you know someone else with the same
sonar nearby in the marina, have him fire up his sonar then look at the
oscilloscope on the test transducer to see if you can see his pinging
reflecting off the bottom.  If you see nothing, take your sonar head
over and plug it into his transducer to see if your head is working.  If
it is, bad transducer...or bad transducer cabling.  it's not rocket
science.

Sorry I was late replying.  I was sailing up 80W from S Fl bringing
someone's Jeanneau 40DS home with them...(c;