Author Topic: Super long array  (Read 18334 times)

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Offline wreckreationaldivers

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Super long array
« on: May 03, 2013, 01:44:03 PM »
Does anyone know what frequency Lowrance operate the down piezo in the LSS-2 and has anyone thought of using the piezoís out of the LSS-2ís to make extra longer arrays? Looking at the X-ray I estimate the piezo lengths to be 200mm, and the quick test using an oscilloscope shows all 3 to have the same signature, if all 3 can be joined it would make the array of industrial length.

Also does any now what problems I might encounter trying this project?


Offline Rickard

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Re: Super long array
« Reply #1 on: May 03, 2013, 03:51:48 PM »
Hi,
They use the same frequencies in all three channels, 455 and 800 kHz. This is actually a problem for them because since they also transmit and receive at the same time they have a tendency to interfere with each other. I use the LSS-2 with my Humminbird omitting the stupid downscan element with very good results. I wasn't sure the downscan element was the same as the others, but from your x-ray it looks as if it is. (I don't think they are single elements, probably at least two in each array). It would be a cost effective way to get elements if all three can be used, cheaper than sacrificing two Humminbird sideimaging transducers like I did when building my "very long array".
 
Problems may have to do with impedance mismatch since you must choose between wiring them in a serie or in parallell. None of those solutions will give the same properties as in a single element. The effect of such mismatch could be reduced efficiency, but it would probably not damage the unit. I have tested several wiring schemes with arrays with large circular elements and couldn't see anything but small differences in the images. Other problems have to do with mixed up pooling directions, damaged solderings, damaged silver coating and difficulties with lining up the elements while the resin cures. With some patience and precision I'm sure your project will be successful.
 
I must say I'm curious to see the result of this!
 
Rickard
« Last Edit: May 04, 2013, 03:27:28 AM by Rickard »

Offline wreckreationaldivers

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Re: Super long array
« Reply #2 on: May 05, 2013, 01:31:20 PM »
Thanks Rickard.

I am glad to hear that all three elements use the same frequencies; my original plan was to make a longer array by using the side elements out of two LSS-2ís, but if all three elements are the same I might as well use them and make one 3 timeís the length.

I hadnít thought about connecting them in series, I was going to connect them in parallel as in the Humminbird which I stripped apart, Am aware of the differences between resistors and capacitor in either case, but what are the characteristicís differences between series and parallel in piezoís?

Looking at your very long array project I can wires connected to the elements but can make out if they are series or parallel how are they connected?

I am to use these on a fish with a long cable so ultimately Iím after strong returns and good images.

Jeff

Offline Rickard

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Re: Super long array
« Reply #3 on: May 05, 2013, 02:12:20 PM »
Hi Jeff,
 
I made a quick sketch to show how the elements are wired. I'm not really an expert on electronics, but this is what people with insight into sonar design have told me. This wiring will result in the same over-all impedance as in a single element. I have made all connections outside the array body to be able to test other wirings if necessary.
 
I went out to test the 'naked' epoxi array after removing the aluminum profile and it worked well with some extra ambient noise. This is my most disburbing issue right now, noise. It could be 'ringing' or simply bad sound insulation in unwanted directions. Insulation can be improved, but I don't know how to reduce ringing. Connecting all elements in parallel?
 
Rickard
 

Offline wreckreationaldivers

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Re: Super long array
« Reply #4 on: May 06, 2013, 01:13:28 PM »
Rickard

Iím not a sonar expert myself, but have a bit of electronic knowledge, whilst the overall impedance will be the same connecting 2 elements in series will double the amplitude thus it may be more than the head unit is designed to see.

Another quick thought is if connected in series is there a possibility of one piezo reverse powering the one itís in series with?

As with the aluminium roughing and cleaning the surface before bonding should improve bond

Jeff

Offline wreckreationaldivers

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Re: Super long array
« Reply #5 on: June 03, 2013, 01:41:19 PM »
Finally got round to opening the LSS-2, but damaged 3 out of the 9 piezoís,  each array contained 3 piezoís , it proved to be a harder than I had first imagined, main problem is the filling material being black thus I was cutting away stuff blind most the time, also the 3 piezoís are very close together. I have however leant a lot and the next should prove too difficult.

As you can see the centre array hasnít got screening on the sides, only the SI element have side screening, also pictured is the LSS-2 elements against the HDSI and a PCB cable end?

Offline Rickard

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Re: Super long array
« Reply #6 on: June 03, 2013, 02:26:30 PM »
Very interesting Jeff!
 
What kind of screening is there around the SI elements? Foil or sheet metal? It looks as if some sort of foam is used between the elements and the screen, is that correct? That black fill inside the transducer, is it hard or soft like in the HB transducers?
 
My own project has been halted for a while because of too much work, but I will go on soon with testing out how ground should be arranged. The signal is still too weak.
 
Rickard

Offline wreckreationaldivers

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Re: Super long array
« Reply #7 on: June 03, 2013, 02:39:48 PM »
Rickard

The SI array is screened by sheet metal (steel), and a double side adhesive foam between, its almost the same the HDSI just longer and 3 piezo's instead of 2.

The black fill is slightly harder than the HDSI, I used slight heat to make it less hard.

I'm sure I broke 3 piezo's getting the hard plastic cover off, I should of used acetone and a little more patience.

Jeff

Offline rnvinc

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Re: Super long array
« Reply #8 on: June 04, 2013, 06:12:56 AM »
I'm curious as to why the downward array is not shielded...

Rickie

Offline abraquelebout

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Re: Super long array
« Reply #9 on: June 04, 2013, 10:53:51 AM »
yes very interesting
i note there's no wire in one side of the ducer, an arrangement like rickard do before the Lss2 may be possible....
for moment i use Lss2 in direct with no modification
hey, i made my 1000eme scan this week, good result
i think the lls2 ducer make a bad return in few meter above the vertical, may be the shape of the ducer, a polished one does give better image
in 455 khz it's not a problem but at 800 khz yes.

Offline Rickard

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Re: Super long array
« Reply #10 on: June 04, 2013, 01:50:56 PM »
Jeff,
 
Can you tell the dimensions of the elements, width and thickness? It looks as if the downscan element is a little narrower than the sidescan elements. That could make it difficult to join all three arrays into one super long array.
 
If I know the width I can calculate the vertical shape of the beam and possibly explain why there is a bad sector at 800 kHz.
 
Rickard

Offline wreckreationaldivers

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Re: Super long array
« Reply #11 on: June 05, 2013, 01:40:32 PM »
Rickie,

The centre elements does have a shield, its on the rear (surface pointing) only, its just not got shielding on the sides

Rickard

Attached are the element dimensions...

What did you use as insulation between the elements and the shield for your very long array? and was the aluminium pre bent or did you form it afterwards?

Jeff

Offline Rickard

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Re: Super long array
« Reply #12 on: June 05, 2013, 04:27:07 PM »
Thanks Jeff,
All elements are identical, good. I think you can use also the broken elements. Just glue or solder wires to where wires are missing, and keep the gap between elements as narrow as possible.
In my long array the elements are wrapped in cork (1.5 mm) on three sides. There is cork also between the element ends. The space between the cork and the aluminum bar is filled with epoxy. I'm not sure this is the best design. A ground shield/screen should perhaps be closer the elements like they were in the transducers. I have problems with bad epoxy-aluminum bond and water ingress between the epoxy and the bar. The aluminum U-bar is an extruded profile. Cork and epoxy are effective insulators.
 
Rickard

Offline Rickard

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Re: Super long array
« Reply #13 on: June 06, 2013, 03:21:44 AM »
Ok,
Here is a figure that describes the vertical shape of the SI beams in the Lowrance LSS-2 at 455 and 800 kHz. The simulation is done to -60 dB. Note the null in the 800 kHz beam. This null can cause a dark band in the image. The blue line represents the sound window, that is, the surface of the element. The inclination is assumed to be 30 degrees from horizontal, like in the HB transducers. Only one beam is shown, the other would mirror this beam pointing to the left.
 
Rickard

Offline rnvinc

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Re: Super long array
« Reply #14 on: June 06, 2013, 05:21:31 AM »
Rickard...in your depiction...

Why does the 455 indicate recognizable side lobes and the 800 does not...??

Rickie

Offline Rickard

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Re: Super long array
« Reply #15 on: June 06, 2013, 05:43:37 AM »
Rickie,
It's the other way around, no sidelobes appear at 455 kHz. This is just what wave theory predicts. It's hard to explain by other means than with pretty awkward formulas. As a general rule, wide sound window and high frequency give many sidelobes. That's why 800 kHz transducers have narrow elements, to avoid too many sidelobes.
 
Rickard

Offline rnvinc

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Re: Super long array
« Reply #16 on: June 06, 2013, 07:13:29 AM »
Rickie,
It's the other way around, no sidelobes appear at 455 kHz. This is just what wave theory predicts. It's hard to explain by other means than with pretty awkward formulas. As a general rule, wide sound window and high frequency give many sidelobes. That's why 800 kHz transducers have narrow elements, to avoid too many sidelobes.
 
Rickard

You are correct Rickard ...I had them listed backwards...

Your description is plenty adequate for my small level of acoustic understanding...

I find this technology interesting and learn a little more each day...thanks to you and others here...

One curious question in my mind is in relation to 2 frequencies coming from 1 element (at separate times of course)..

Is the electrical signal going to the element from the unit what determines which frequency wave (455 or 800) is emitted thru the water...??

Rickie
« Last Edit: June 06, 2013, 07:19:33 AM by rnvinc »

Offline Humminbird_Greg

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Re: Super long array
« Reply #17 on: June 06, 2013, 09:47:06 AM »
Yes it does Rickie.  Though to work well the element needs to be designed to work with that frequency.
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Offline rnvinc

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Re: Super long array
« Reply #18 on: June 06, 2013, 09:54:40 AM »
Yes it does Rickie.  Though to work well the element needs to be designed to work with that frequency.


Thanks Greg...that makes sense...

Rickie

Offline wreckreationaldivers

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Re: Super long array
« Reply #19 on: June 06, 2013, 10:14:32 PM »
Rickard

Is the simulation for a standard Lss-2? and how does it compare with a standard HDSI?, what will be the effect of making a long array?

Jeff

Offline Rickard

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Re: Super long array
« Reply #20 on: June 07, 2013, 12:18:08 AM »
Jeff,
 
The simulation is for a standard LSS-2. But the result should be valid for any transducer with 3.2 mm wide elements, independent of array length. The 30 degree inclination is used in the standard transducers. I don't know the width of the elements in the HB HDSI, but I think it is close the width used in the LSS-2. If anyone knows the width in the HDSI I can simulate that transducer too.
 
The vertical beam form does not change in a long array, only the horizontal beam will be narrower.
 
Rickard

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Re: Super long array
« Reply #21 on: June 07, 2013, 11:13:15 AM »
hi rickard
the array are the same 3,2 mm
i find this picture in 800Khz Lss2
whe can see the null effect..
when i use the 800khz i must get the target over 5 meter distance in left or right array, after i have a good result
next week i make good picture of an old wreck ballast at 800 khz in 20 m depht
the ducer is at 5 m than ground and i make 30 m scan on left and right
i think there's 3 m in the null zone at 5 m
thanks for the study of the array, it's interresting

Offline wreckreationaldivers

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Re: Super long array
« Reply #22 on: June 07, 2013, 01:25:53 PM »
Rickard

Is it possible to fix element side to side & paralleling them up to making a double width array, if so would be the effect at 455hz & 800hz & does the HDSI give evidence of the same null when scanning/recording?

Jeff

Offline Rickard

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Re: Super long array
« Reply #23 on: June 07, 2013, 01:57:22 PM »
Jeff,
 
Yes, the elements could be arranged like you say. The result would be the same as with 6.4 mm wide elements. The figure shows what would happen and you can see that there will be many more nulls and sidelobes at both frequencies. I have inspected many 800 kHz images from the HDSI transducer, and the null bands are clearly visible. The null sector is not as clear in a practical transducer as theory tells. A number of other factors, like the resin in the sound window makes the null sector much fuzzier than one would expect.

Abra, the null sector is the dark band at the right end of the double arrow in your image. In a slant range corrected image this band is streched out and becomes even more disturbing.

Rickard
 
 
 
« Last Edit: June 07, 2013, 02:01:55 PM by Rickard »

Offline wreckreationaldivers

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Re: Super long array
« Reply #24 on: June 19, 2013, 12:48:20 PM »
Some marine engineers I have spoken to say that they have fitted basic transducers in pots of oil/ultrasonic gel which is then fitted in the bilge of GRP hulls and had good results, they say any un-aerated epoxy/sealant would work.

I was thinking of encasing the DIY array in wax for testing, this way easy access can be gained for further mod's before final epoxying

Obviously wax wouldn't wear well and dent,s easy, but could wax work?

Offline Rickard

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Re: Super long array
« Reply #25 on: June 19, 2013, 01:20:14 PM »
Yes, I have seen such arrangements too, with tranducers in oil. This method is sometimes used in in-hull applications when the hull is v-chaped making it difficult to position the transducer.
 
Wax should work since sound speed in wax is about 2200 m/s which is close to sound speed in most epoxies. To have the best thickness matching the wax layer should not exceed 3 mm, though. This has to do with trying to be close 1/4 of a wavelength and away from 1/2 wavelength.
 
Rickard

Offline wreckreationaldivers

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Re: Super long array
« Reply #26 on: August 07, 2013, 10:10:14 PM »
After stripping transducers I have 3 sets of 3 peizo's (9 long) and 8 singles.

I'm now at point of soldering the peizo's together, luckly I tested soldering some broken peizo's first, frustratingly difficult as the contact surface seems burn away before soldering is achieved.

Anyone got tried and tested techniques? I'm running out of test pieces

Jeff

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Re: Super long array
« Reply #27 on: August 08, 2013, 09:12:37 AM »
Try melting the solder on the soldering iron tip and touching the tip to the element.  Allow to cool.  Melt the solder on the element and insert wire (quickly!).  Allow to cool.  Everything need to be pretty clean for this to work well.
Greg Walters at Humminbird
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Offline wreckreationaldivers

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Re: Super long array
« Reply #28 on: August 08, 2013, 02:22:22 PM »
Success thank Greg,  extra low heat and a globe of solder on the tip does it, 3x3 now soldered :-)

Offline Rotus623

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Re: Super long array
« Reply #29 on: September 30, 2014, 10:31:45 AM »
Wreckreation, did you ever finish up this product? Just curious this is an interesting thread.....

Offline wreckreationaldivers

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Re: Super long array
« Reply #30 on: August 23, 2016, 02:25:07 PM »
The project stalled for quite some time due to other commitments and as i was get some good results from the lSS & HDSI combo there was no great need to progress with it. (I was always told not to break something which it working).

But after loosing the fish as a result of the tow wire being guillotined by the boats prop, i am now missing scanning wrecks before diving them.
I am now progressing the super long array...

Here's a photo of the constructed array prior to casting.

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Re: Super long array
« Reply #31 on: January 10, 2018, 07:19:29 AM »
Any luck with the new, longer array?



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