Any info about depth sounders?
MikeC
Sorry if this appears twice - my server just told me it didn't send the
first one.
Can anybody give any advice, or preferably a schematic for a depth sounder
for a boat?
I want to design a combined speed/distance log and depth sounder using sound
waves through the water, but this is an area that I haven't been into
before. I can get ultrasonic transducers from Maplin, but I don't even know
if ultrasonic is the best frequency to use. All those old films of people
sweating in submarines while the destroyer above tries to sound them out,
used an audible 'ping'. Is that a more trasmissive frequency to use in sea
water, or was it just that ultrasonics wasn't really available during the
last world war? When I find the best frequency to use, how many cycles
should in build into the ping? An echo from a hard bottom probably isn't too
difficult, but if the botton is soft mud?
The other thing is - the ultrasonic transducers from Maplin normally work in
air. What is the best way to couple the sound to the water - by having an
air gap in front of the transducer, or by potting the transducer in a tube
full of waterproof potting compound which dips into the water?
I'm really on the footslopes of the learning curve on this one, so any
guidance would be appreciated.
Thanks,
Mike.
--
WARNING - My e-mail return address is bogus to avoid having it read by
automatic spam address gatherers.
Mental decription should not be too taxing, though:
Mike*e-col#ntlworld*com
where * = 'dot'; # = 'at'
Fred Bloggs
MikeC wrote:
> ............ An echo from a hard bottom probably isn't too
> difficult, but if the botton is soft mud?
Exactly!- The sound waves have been known to stick!
Winfield Hill
>
> Can anybody give any advice, or preferably a schematic for a depth
> sounder for a boat?
Visit a marine supply store and ask to see the manuals of the depth
sounders/fish finders, which often include schematics at the back.
Most use 200kHz transducers. The attenuation in sea water at this
frequency is about 60dB/kyd so a 500 yard range is practical if the
beam is narrow enough. High frequencies like 200kHz are preferred
in part because one can easily make small directional transducers.
Because transducer mount design is a big deal for a boat, you can
usually purchase just the transducer at marine supply stores. Don't
try to adapt an air transducer for underwater use, because they have
very different acoustic impedances.
Deep Sea (8-mile range) depth-sounding transducers are usually at
low frequencies like 10-12kHz, where the attenuation is 0.5 dB/kyd,
or about 100x less. However they are large, expensive beasts.
> All those old films of people sweating in submarines while the
> destroyer above tries to sound them out, used an audible 'ping'.
> Is that a more trasmissive frequency to use in sea water, or was
> it just that ultrasonics wasn't really available during the last
> world war?
Submarine sonars are usually flexible, with a frequency settable to
take into account the intended use and range.
> When I find the best frequency to use, how many cycles should in
> build into the ping?
Usually 3 to 20 cycles are used, to avoid smearing the echo and to
maintain high resolution. It's also a matter of receiver bandwidth.
Fairly high power is used during the ping, e.g., 200 watts minimum.
Because piezo-ceramic transducer acoustic impedances are different
than water, power-coupling is limited and the transducer looks like
a capacitance to the driver. This is why resonant drive circuits
are usually used.
> An echo from a hard bottom probably isn't too difficult, but if the
> bottom is soft mud?
Sandy bottoms scatter nearly as well as rocky bottoms, if the angle
of incidence is 90 degrees. Silty bottoms are down about 6dB and
saturated clay bottoms are down about 12dB more, which means that
a rather strong echo can still be observed.
If you are serious about in learning about these things, buy a copy
of Robert J. Urick's book "Principles of Underwater Sound."
Thanks,
- Win
Winfield Hill
>
> Most use 200kHz transducers. The attenuation in sea water at this
> Deep Sea (8-mile range) depth-sounding transducers are usually at
> low frequencies like 10-12kHz, where the attenuation is 0.5 dB/kyd,
> or about 100x less.
Sorry, I meant to say about 60dB/kyd better. The transmission is
"poor," 1/1000 per 1000 yards at 200kHz, whereas it's down only 6%
per 1000 yards at 10kHz. Of course these numbers ignore spreading
loss attenuation, which generally dominates in the sonar equations.
Thanks,
- Win
Joe McElvenney
I'm sorry but a very OT question brought on by the thread -
> sweating in submarines while the destroyer above tries to sound them out,
> used an audible 'ping'.
Watching old colour documentaries about US submarines in the Pacific during
WWII, I notice how rusty they became during service. So then, how did they
keep the deck gun from becoming all rusted-up? I presume that during a crash
dive they wouldn't have time to plug the barrel or slap grease on everything.
And, although I know something of gun construction, I don't remember stainless
steel being a preferred material.
The only submariner (one of the modern atomic variety) I asked this question
of just said, "What gun?"
Cheers - Joe
John Fields
wrote:
> If you are serious about in learning about these things, buy a copy
> of Robert J. Urick's book "Principles of Underwater Sound."
---
Albers' "Underwater Acoustics" and "Underwater Acoustics Handbook"
and Leon W. Camp's "Underwater Acoustics" are good, too.
---
John Fields
Professional circuit designer
http://www.austininstruments.com
Martin Griffith
scribbled:
>Good Folk,
>
>Sorry if this appears twice - my server just told me it didn't send the
>first one.
>
>Can anybody give any advice, or preferably a schematic for a depth sounder
>for a boat?
loads of "stuff" on their web site
Hiroshima 45, Tchernobyl 86, Windows 95
James Meyer
wroth:
Most of the WWII pig boats were surface ships that submerged
occasionally to attack or to keep from being attacked. There was plenty of time
to do routine maintenance topside. Maximum time submerged was only 10 to 12
hours.
Jim
Richard Dungan
>Can anybody give any advice, or preferably a schematic for a depth sounder
>for a boat?
>I want to design a combined speed/distance log and depth sounder using sound
>waves through the water, but this is an area that I haven't been into
>before. I can get ultrasonic transducers from Maplin, but I don't even know
>if ultrasonic is the best frequency to use. All those old films of people
>sweating in submarines while the destroyer above tries to sound them out,
>used an audible 'ping'. Is that a more trasmissive frequency to use in sea
>water, or was it just that ultrasonics wasn't really available during the
>last world war? When I find the best frequency to use, how many cycles
>should in build into the ping? An echo from a hard bottom probably isn't too
>difficult, but if the botton is soft mud?
Most commercial echo sounders use frequencies from the high tens to the
low hundreds of kilohertz. The lower frequencies give you more range at
the expense of resolution.
I suspect that a lot of the WW2 kit operated at low frequency because
the technology could not cope with anything higher, and also because if
it remains audible, some of the processing can be delegated to the human
brain.
>The other thing is - the ultrasonic transducers from Maplin normally work in
>air. What is the best way to couple the sound to the water - by having an
>air gap in front of the transducer, or by potting the transducer in a tube
>full of waterproof potting compound which dips into the water?
You might be better off getting a replacement transducer for a marine
sounder. Furuno come to mind, but there are many others. I think that
the modifications would kill your Maplin air sounders.
At one time NatSemi made a chip for basic echo sounder applications, the
LM1812. Please email me privately, avoiding the spam trap, if you cannot
find a data sheet and applications.
So far as your log is concerned, you can extract the speed over the
bottom by measuring the doppler shift of the received echoes. There is a
great deal more to it at the serious end of the market, but that should
not worry you.
Richard
------------Richard Dungan-------------
Radix Electronic Designs, Orpington, UK
richardATradixDASHdesignDOTcoDOTuk
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