Erratic Indications From Depth Sounder

[Alecadi]

Originally Posted by four winds

Yes it does. Corrosion at a connection serves to add resistance to current flow. It also causes heat buildup, however slight at the current level in a transducer wire. This added resistance could easily alter the reading at the gauge. Since measuring resistance in the transducer is how it works. Granted that is an over-simplification.

Cleaning connections would be a good first step.

Thank you all of you
Once again I find solutions in the CF
I'll let you know then.. (will take a while as next WE I'm out of town.)

[Jim Cate]

G'Day Alec,

I kinda doubt that inaccurate readings are an issue of the transducer being bad.

The way these things work is that the "brain" of the sounder generates an electrical pulse which is passed on to the transducer. The transducer generates an audio pulse at (usually) either 50 or 200 KHz, and this audio pulse travels through the water to the bottom. Some of the audio pulse is reflected back up to the transducer, which "hears" the sound and converts it back into an electrical pulse, and this is sent back to the "brain". The brain then measures how long it took to make the round trip. Knowing the velocity of sound in water, it can calculate the distance to the bottom, which it then kindly displays for you. It repeats this sequence frequently.

Nowhere in this process is it required to measure voltages, only time intervals, and in my experience transducers either work ok or not at all.

Bubbles, turbulence, thermoclines and other phenomena between the surface and the bottom can indeed cause false readings, but these are always LESS than the true depth. In the case of readings greater than the true depth, I'd tend to suspect a problem in the electronics... perhaps a fault in the clock rate or something else that
induces a timing error. It can't hurt to clean up all the connections, but I wouldn't throw my back out doing it! The good news (I think) is that you shouldn't have to pull the transducer out to fix the problem... just the electronic box.

At any rate, good luck with it.

Cheers,
Jim

[Alecadi]

Originally Posted by Jim Cate

G'Day Alec,

I kinda doubt that inaccurate readings are an issue of the transducer being bad.

The way these things work is that the "brain" of the sounder generates an electrical pulse which is passed on to the transducer. The transducer generates an audio pulse at (usually) either 50 or 200 KHz, and this audio pulse travels through the water to the bottom. Some of the audio pulse is reflected back up to the transducer, which "hears" the sound and converts it back into an electrical pulse, and this is sent back to the "brain". The brain then measures how long it took to make the round trip. Knowing the velocity of sound in water, it can calculate the distance to the bottom, which it then kindly displays for you. It repeats this sequence frequently.

Nowhere in this process is it required to measure voltages, only time intervals, and in my experience transducers either work ok or not at all.

Bubbles, turbulence, thermoclines and other phenomena between the surface and the bottom can indeed cause false readings, but these are always LESS than the true depth. In the case of readings greater than the true depth, I'd tend to suspect a problem in the electronics... perhaps a fault in the clock rate or something else that
induces a timing error. It can't hurt to clean up all the connections, but I wouldn't throw my back out doing it! The good news (I think) is that you shouldn't have to pull the transducer out to fix the problem... just the electronic box.

At any rate, good luck with it.

Cheers,
Jim

Hi Jim
And as always thank you for the help... but here we are at the Peter principle for me: we passed my incompetence threshold.. (by far!!)
"brain" .."electronic box"...
oups...
I'll have to get a specialist to have a look then....
Alec

[Arcady]

Alecadi,

Is your transducer cable bundled up with any other electrical cables?

Although in theory shielded cables are exactly that, in reality cross-talk sometimes occurs if another cable in close proximity is carrying significant voltage or current fluctuations. I've even seen supposedly shielded electronics modules badly affected when too close to radar antennas. I wonder if there is any equipment that you (or even close neighbours) might have installed recently that is being used during the times you experience erratic readings.

Just a thought.

[four winds]

Actually, I would suggest that the transducer transforms the electrical impulse from the "brain" into a sound wave, then "hears" the echo and transforms the echo back into an electrical impulse for the brain to measure the time interval. Just as stated above.

However, an erratic electrical connection to the transducer can inhibit the brains ability to interpret the impulse timing properly. Either by resistance (from corrosion) that lowers the voltage level of the pulse to the point it can't be detected, or intermittent open circuit conditions (a broken wire that still touches ends unreliably) that drop the transmission of the pulse completely. It attempts to interpret the timing to the best of its ability given bad information and erratic readings are a result. In this case the transducer is working properly, it's just unable to send the information reliably to the brain.

The pulse must have sufficient waveform amplitude to be detected, so in effect it is sensitive to the voltage level of the pulse. Even if it's not measuring it per se, it is detecting pulses of a predetermined threshold level.

Not saying it's definitely the problem, but checking for corrosion of the connections and proper continuity throughout is a good first step.

[Alecadi]

Originally Posted by Arcady

Alecadi,

Is your transducer cable bundled up with any other electrical cables?

Although in theory shielded cables are exactly that, in reality cross-talk sometimes occurs if another cable in close proximity is carrying significant voltage or current fluctuations. I've even seen supposedly shielded electronics modules badly affected when too close to radar antennas. I wonder if there is any equipment that you (or even close neighbours) might have installed recently that is being used during the times you experience erratic readings.

Just a thought.

Thanks for the advice
I'll have to check that also
Alec

[four winds]

Originally Posted by Arcady

Alecadi,

Is your transducer cable bundled up with any other electrical cables?

Although in theory shielded cables are exactly that, in reality cross-talk sometimes occurs if another cable in close proximity is carrying significant voltage or current fluctuations. I've even seen supposedly shielded electronics modules badly affected when too close to radar antennas. I wonder if there is any equipment that you (or even close neighbours) might have installed recently that is being used during the times you experience erratic readings.

Just a thought.

And it's a good thought. In this case one would want to look for a break in the shielding of any coax cable involved. A broken shield at a coax cable end effectively disables or reduces the ability of the shield to perform its function.

[Alecadi]

Originally Posted by four winds

And it's a good thought. In this case one would want to look for a break in the shielding of any coax cable involved. A broken shield at a coax cable end effectively disables or reduces the ability of the shield to perform its function.

Thanks , as soon as I'm back to the boat I'll check that.
Alec

[Alecadi]

The deep sounder is working properly at this time, done 146 nm in 3 days and was working perfectly...

The strange thing is that i did nothing to correct the problem so far?
There is a gremlin in my depth sounder !!