What output should I expect on a depth sounder transducer?

I have been tasked with troubleshooting a problem with a depth sounder on the boat of a friend.

They have yet to pull the boat so I have not even had a chance to look at it. Just trying to understand waht I am getting into after they pull and I need to work on the problem.

What output should I expect on a depth sounder transducer? Is it a simple voltage level change with depth or would I expect to see some kind of waveform?

It is a short duration ultrasonic pulse, sent out of the transducer at a high amplitude by a circuit in the sounder, then received at a much lower amplitude after reflecting off of the 'bottom' (or whatever else).

It will actually work somewhat in the air, like reflecting off of a concrete floor. The distance will show up as much more than the actual distance because of the slower speed of the pulse in air, and the magnitude will be lower, but should work at relatively short distances.

If you don't have anything to reflect the pulse, and if it is not far enough away to avoid being 'swamped' by the outgoing pulse, then you won't see anything.

Thanks yeah I know what should be coming out of the transducer itself. I guess I was looking for what should be the output of the transducer and input to the receiving / display unit.

Hi Spinnaker, It would help if you could get a circuit diag for the unit. Ive posted a very old paper sounder for explination purposes & wave forms. On this unit there is a 330V 1ms pulse shown on the transducer. On Q201 base there is 1.2v pulse being picked up by the transducer. The principals for transmition & reception on this old machine are still relevent to modern units. Sugest you actualy obtain a circuit for the unit you are working on if posible. Daryl.

spinnaker said:

Thanks yeah I know what should be coming out of the transducer itself. I guess I was looking for what should be the output of the transducer and input to the receiving / display unit.

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When I worked for Hughes installing sounding devices we normally checked the unit for leakage/insulation breakdown and transducer impedance before installing it on a ship using a procedure like this. http://www.syqwestinc.com/support/Transducer_Cable%20checks.pdf

http://www.ndt-ed.org/EducationReso...rasonics/EquipmentTrans/tranducertesting1.htm

Frequency and resistance spec's vary with the transducer type. The megger check is for a larger sounder, so a simple resistance check might work for a small boat unit.

Most modern transducers are Piezo type so there is no resistance to measure. A quick way to check if the transmitter stage & transducer are working is to feel the face of the transducer with the sounder running, you should be able to feel the pulses, or hear the transducer ticking. If you have an CRO using the most sensitive setting & conect to the disconected transducer & tap the face of the transducer with a screwdriver handle, the trace should atleast jump when the transducer is tapped. Just some pointers. Daryl

DonQ said:

It is a short duration ultrasonic pulse, sent out of the transducer at a high amplitude by a circuit in the sounder, then received at a much lower amplitude after reflecting off of the 'bottom'...

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It is a short duration: Milliseconds
ultrasonic: well abouve 20kHz
pulse: redundant, already said short duration
sent out of the transducer: an electronic device so the signal in the wire is an electronic signal, usually a voltage. Ultrasonic and pulse still apply.
at a high amplitude: the scale will be in volts, or tens of volts
by a circuit in the sounder: redundant
then received: and converted back to a voltage again
at a much lower amplitude: no longer tens of volts, closer to millivolts
after reflecting off of the 'bottom': and keeping its ultrasonic and pulse characteristics, just like you would expect from an echo.

In other words: A high frequency, short duration, electric signal, with lots of volts, outgoing...
followed by a nearly identical electric signal, only now at a fraction of a volt, coming back.