Surf PI - Looked at decay curve when dunking coil in saltwater ... was not as dramatic as I thought

[Polymer]

Instead of coating the PC board in wax try a conformal coating. All the boards we used in seismic work in the Louisiana swamps were coated with it. It can be pried off a component if you need to replace a part, then paint over the new part and PC board, both sides, in the repaired area.

Thanks! Got a can of spray "Urethan71". It works for me.

[Goaty]

@Polymer

Where did you place the indicating LED?

The LED is near the switches but I am also not happy with it’s visibility.






I think the visibility of it decreases in water because the rounded end is a lens and this no longer focusses the light into a narrow beam when submerged.
This is probably due to the refractive indices of the plastic lens and water being very similar so the light simply radiates over 180 degrees from the point source (chip).


In his underwater Pickini Bernard used an internal loud piezo buzzer in conjunction with a simple driver transistor circuit. I guess there was sufficient sound transmission through his waterproof case to make it audible under water but it would probably be fairly ‘heavy’ on batteries.
Also, the thicker PVC pipe housing you and I have used may attenuate the sound more than his case.

How did your search by the sea go?

I haven’t had much opportunity to test mine as I haven’t been particularly well for the last couple of months and the low winter water temperature probably wouldn’t have helped my recovery.
At least it’s starting to warm up now!!

I will look forward to seeing you solutions.

[Polymer]

@Goaty

I wish you a great recovery! Can understand you don't want to go into cold water yet. Have been there myself.

Thanks for the picture. Looks like you have a PP mode aka static mode on the switch?

My LED is bright enough and I filed it to around 45 degress so it faces to me.
I will be installing a fiberoptic down to the coil to get the same "depth of viewing" for the coil and LED an see how that goes.
Couldn't be bothered insulating two wires all the way down and waterproofing that too.

If I understood you properly, you want to snorkel because the swells are a bit tough whilst standing up and detecting.

Well, I felt like a piece of seeweed being dragged around in the moving water whilst snorkel detecting and am building another
to do the same as you did before, namely standing up. I am laughing right now wondering if I should better get a big backhoe and a mega sieve
and get it done with .... but I do enjoy detecting and experimenting.

Here two pics of my LED:

[Goaty]

I wish you a great recovery! Can understand you don't want to go into cold water yet. Have been there myself.

Thanks! The water and air temp is just starting to warm up - I had my first surf in 8 months yesterday. It was nice to get back in the surf but I think I over-did it as every muscle is aching today!

Looks like you have a PP mode aka static mode on the switch?

Yep! - works well as long as I remember to switch back to 'motion' when I continue searching. This SOB (silly old b...) tends to be a bit forgetful in his old age!

I will be interested to hear how the fibre goes. I guess you could always bring it up to your dive mask to have the optical version of underwater headphones .

wondering if I should better get a big backhoe and a mega sieve
and get it done with

Brute force and ignorance usually works well - trouble is it tends to upset the do-gooder 'Greenies'

I felt like a piece of seeweed being dragged around in the moving water

I know the feeling well as I surf a Wave-ski which is a surf board which you surf sitting down and strapped on with a seat belt. I'd describe it as being strapped to an ironing board and dropped into a washing machine.

[Polymer]

I wish you a great recovery! Can understand you don't want to go into cold water yet. Have been there myself.

Thanks! The water and air temp is just starting to warm up - I had my first surf in 8 months yesterday. It was nice to get back in the surf but I think I over-did it as every muscle is aching today!

My muscles aren't aching as much as they did at the beginning of water detecting ... I could hardly move. The retrieving the target has me thinking too.
That's actually quite a challenge to put it mildly, because of heaps of rocks and clay where the good stuff sits under the thin sand layer.
I am redefining what a good scoop is under these circumstances. Wonder where this will lead.

I will be interested to hear how the fibre goes. I guess you could always bring it up to your dive mask to have the optical version of underwater headphones .

The fibre went well and is much better than the LED postion before, because the light indicator has roughly the same optical depth as the coil now.
It was a quick job and has survived 5 hrs now with a hefty swell coming in the last hour and the detector and me getting thrown often. Went bodysurfing later on with the Misses.
I am more confident now in the watertightness of my design after that beating. I am still not happy with the "holding" ergonomics though, got sore hands. Pipe to thick.

Here's some pics of the fibreoptic. Wanted bright blue, but I drilled a little to deep into the led for the fibreoptic (dia. 3mm) and destroyed that one. Have to get new LEDS.
I might get sheathed fibre next time. This one you can bend with heat, it's PMMA. Here some pics:

wondering if I should better get a big backhoe and a mega sieve
and get it done with Brute force and ignorance usually works well - trouble is it tends to upset the do-gooder 'Greenies'

No Worries, it will be painted green and runs on organic soybean oil and has some PV's attached too.
Did I forget to mention that I am retrieving TOXIC metals like lead from the ecosphere ... special beach cleaning as I like to call it.
Don't get me wrong. I am for cleaning up/not causing environmental havoc. From my perspective many of the things being done
in the name of "environment" are just greenwashing BS and are not really serving nature or humanity very well.

I felt like a piece of seeweed being dragged around in the moving water
I know the feeling well as I surf a Wave-ski which is a surf board which you surf sitting down and strapped on with a seat belt. I'd describe it as being strapped to an ironing board and dropped into a washing machine.

Interesting sport by the looks of it! Looked it up, didn't even know this existed before you mentioned it. Sounds tough though when you get dumped in a wave.

[Polymer]

Although sea water is a very poor conductor relative to metal objects, it is the spherical volume that the search coil energises that accounts for the length of the decay. Small coils will energise less volume and give a faster decay. Large coils, such as the 42 inch square coil mounted on a sled, in 50ft of water will have a decay reaching out to 200uS. This coil was used to locate 70 pound silver bars which have a decay of their own out to 8 milliseconds, so the late sampling of 250uS did not matter.

Eric.[ATTACH]41259[/ATTACH]

Thank you for your reply and the picture. An impressive construction.Was the creation of that coil a lot of trial and error or did it work electrically/mechanically off the bat after concept/design?

If I am understanding what you have written properly then a salt water sphere somehow holds on to the energy more than say an air or sweet water sphere.
Can one imagine the effected water sphere as being analog to a giant ball made of tinsely aluminium foil bits?
I am wondering if this "holding on" is just an eddy current phenomena and/or something else. This surely has me curious.

[green]

Thank you for your reply and the picture. An impressive construction.Was the creation of that coil a lot of trial and error or did it work electrically/mechanically off the bat after concept/design?

If I am understanding what you have written properly then a salt water sphere somehow holds on to the energy more than say an air or sweet water sphere.
Can one imagine the effected water sphere as being analog to a giant ball made of tinsely aluminium foil bits?
I am wondering if this "holding on" is just an eddy current phenomena and/or something else. This surely has me curious.

I'm curious too.

Salt water is conductive and looks like a target. In terms of raw phase, it comes in around 15 degrees, same as small bits of foil. from another thread

http://www.geotech1.com/forums/showt...665#post208665 a thread on salt response

Large coils, such as the 42 inch square coil mounted on a sled, in 50ft of water will have a decay reaching out to 200uS.

Small bits of foil would have a decay time constant less than 5usec. Straight line decay linear log chart, 2.3*TC/decade. Target with TC of 5usec would decay 4decades in 46usec,to see signal at 200usec would have to been saturated for maybe 150usec. Signal would be easier to see at 200usec if it decayed straight line on log- log chart. I don't understand salt response, and am probably looking at it all wrong.

[green]

I'm curious too.

Salt water is conductive and looks like a target. In terms of raw phase, it comes in around 15 degrees, same as small bits of foil. from another thread

http://www.geotech1.com/forums/showt...665#post208665 a thread on salt response

Large coils, such as the 42 inch square coil mounted on a sled, in 50ft of water will have a decay reaching out to 200uS.

Small bits of foil would have a decay time constant less than 5usec. Straight line decay linear log chart, 2.3*TC/decade. Target with TC of 5usec would decay 4decades in 46usec,to see signal at 200usec would have to been saturated for maybe 150usec. Signal would be easier to see at 200usec if it decayed straight line on log- log chart. I don't understand salt response, and am probably looking at it all wrong.

No discussion. Made a couple charts comparing decay slopes. Straight line linear-log and straight line log-log to show why it would make more sense if salt decayed straight line log-log if signal can be seen at 200usec. Not saying it does, sure would like to see a salt decay curve out to 200usec+.

[Polymer]

Thanks for the salt response thread green.

Water is indeed a fascinating element and I don't think science fully understands everything about it yet.
Add some pulsed magnetic fields and voila, it gets even more interesting or confusing.

Here a water science site which I find is a good read and may lead to new "AHA's":

http://www1.lsbu.ac.uk/water/magneti...c_effects.html

Here's the main Index in which the above link is hard to find.

http://www1.lsbu.ac.uk/water/water_s...e_science.html

[green]

Polymer, Reply #1 you recorded some good traces. Have you tried subtracting the air trace from the water trace in a program like Excel and charting the result linear-log and log-log?

[Polymer]

Polymer, Reply #1 you recorded some good traces. Have you tried subtracting the air trace from the water trace in a program like Excel and charting the result linear-log and log-log?

No, I havn't. I think my oscilloscope can store values numerically. I would have to read up on this.

[green]

No, I havn't. I think my oscilloscope can store values numerically. I would have to read up on this.

Do some reading. I'll reply with an example later today on how I do it. You need to try on the bench a few times to get some confidence with your test procedure before trying salt water.

[green]

Excel accepts csv which my scope has. Record a no target and a target recording with scope. Copy recordings to Excel. Subtract no target from target recording and chart XY. Depends on no or very little circuit drift between recordings. I try to keep time between recordings to a minimum. scope scale, .5v/div seems to be best with my scope. Both recordings need same trigger at Tx off, your scope recordings reply#1 look like they do. I use Excel because that's what I have, probably other programs that would work. Any questions, ask.

[Polymer]

Excel accepts csv which my scope has. Record a no target and a target recording with scope. Copy recordings to Excel. Subtract no target from target recording and chart XY. Depends on no or very little circuit drift between recordings. I try to keep time between recordings to a minimum. scope scale, .5v/div seems to be best with my scope. Both recordings need same trigger at Tx off, your scope recordings reply#1 look like they do. I use Excel because that's what I have, probably other programs that would work. Any questions, ask.

Hell yes, my oscilloscope can save the current values as data files! Four different types actually. It does 5000 values per file @ 1us/div, 20 divs.
So if I divide this correctly that would mean 250 data points per 1us, or one per 4ns. Is that correct?

Here are my test file examples: dang ... could not upload any of the four test files .bin .csv .txt .xls.

The .txt file is supposedly too big to be uploaded (ca. 168k) and the others are "invalid". Dunno what to do about that.

Anyways, I did manage to get the data into openoffice and make some curves. The graphs are quite lumpy for my taste though.
I have downloaded scilab and will try and get along with that to get some finer detail curves.

Recording with no target in the sea (just decay in saltwater) is relatively easy. Can do that.
Measuring with a target looks like a challenge at say 4m max. depth and keeping the distance equal for all
measurements at say 0.5m depth increments. Any ideas or does it not matter?

[green]

Hell yes, my oscilloscope can save the current values as data files! Four different types actually. It does 5000 values per file @ 1us/div, 20 divs.
So if I divide this correctly that would mean 250 data points per 1us, or one per 4ns. Is that correct?

Here are my test file examples: dang ... could not upload any of the four test files .bin .csv .txt .xls.

The .txt file is supposedly too big to be uploaded (ca. 168k) and the others are "invalid". Dunno what to do about that.

Anyways, I did manage to get the data into openoffice and make some curves. The graphs are quite lumpy for my taste though.
I have downloaded scilab and will try and get along with that to get some finer detail curves.

Recording with no target in the sea (just decay in saltwater) is relatively easy. Can do that.
Measuring with a target looks like a challenge at say 4m max. depth and keeping the distance equal for all
measurements at say 0.5m depth increments. Any ideas or does it not matter?

The sea is the target, no target would be away from the sea in the air. Charting a target on the bench is first, was thinking a 2inch square of regular aluminum foil would be a good place to start. Sample at 5usec/div for the foil. Maybe you could post a picture of your chart with 2inch square regular srength aluminum foil.

You need to be able chart linear-log and maybe log-log if the target doesn't chart straight line linear-log with sea as target. Just my thoughts maybe some knows what the slope is and if it changes with depth.