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

[Polymer]

The swell was finally low today, so I wrapped everthing up and went to the sea.

I've been building a snorkelling Surf Pi and wanted to see what happens to the curves
when it gets in the water.

The results actually amazed me and the signals were not as "influenced" as I feared they might be.

If there are other things to measure in the water or I missed something, ask, I might just do it ...

Anyway here my results (I only took one photo of the setup and I'm even happy about that, cause taking photos distracts me):

[ionut_mtb]

The swell was finally low today, so I wrapped everthing up and went to the sea.

I've been building a snorkelling Surf Pi and wanted to see what happens to the curves
when it gets in the water.

The results actually amazed me and the signals were not as "influenced" as I feared they might be.

If there are other things to measure in the water or I missed something, ask, I might just do it ...

Anyway here my results (I only took one photo of the setup and I'm even happy about that, cause taking photos distracts me):

[ATTACH]41233[/ATTACH]

[ATTACH]41234[/ATTACH]

I would say that you have a good shield with these results. But, from the picture of the coil, i don't know if you have one...

[green]

The swell was finally low today, so I wrapped everthing up and went to the sea.

I've been building a snorkelling Surf Pi and wanted to see what happens to the curves
when it gets in the water.

The results actually amazed me and the signals were not as "influenced" as I feared they might be.

If there are other things to measure in the water or I missed something, ask, I might just do it ...

Anyway here my results (I only took one photo of the setup and I'm even happy about that, cause taking photos distracts me):

[ATTACH]41233[/ATTACH]

[ATTACH]41234[/ATTACH]

Thanks good pictures, haven't got my detector to the beach yet. Looks like you have about .8v change at 10usec and maybe a visible change out close to 20usec. More than I was hoping. Was expecting the decay to be much faster.

[6666]

Thanks for the test, thats something I've been wanting to do for some time.

[Goaty]

Thanks for the test, thats something I've been wanting to do for some time.

[ATTACH]41235[/ATTACH]

Welcome to Australia

[Goaty]

[QUOTE=Polymer;237244]
I've been building a snorkelling Surf Pi



Any chance of some details of your waterproof housing please?

[Tibuck19]

Thanks for the test, thats something I've been wanting to do for some time.

[ATTACH]41235[/ATTACH]

LMAO very good lol

[Ferric Toes]

Thanks good pictures, haven't got my detector to the beach yet. Looks like you have about .8v change at 10usec and maybe a visible change out close to 20usec. More than I was hoping. Was expecting the decay to be much faster.

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.

[Polymer]

Thanks for the test, thats something I've been wanting to do for some time.

[ATTACH]41235[/ATTACH]

great creation 6666, luv it!

Dang, Mr Sharky didn't have any gold teeth ...

[Polymer]

[QUOTE=Goaty;237363]

I've been building a snorkelling Surf Pi

Any chance of some details of your waterproof housing please?

I'd love to, but don't know which details to start with. Give me some pointers please.
Anyway the top,mid,bottom (coil) sections are separately sealed, so if a section goes leaky, it can't spread to the rest.

Still figuring out which wax to drown the pcb in once I've thoroughly end-cleaned it.

[Polymer]

I would say that you have a good shield with these results. But, from the picture of the coil, i don't know if you have one...

Nope, no shield - I hope that's not a "uh oh".

I went the next night to test if the annoying EMI I have on it is still there when coil is in salt water.
It was still there. So I figure it's gotta be something on the pcb. Grrrr...

The ambient temperature was 10 degrees lower this time and was notable on the decay curve or perhaps it was because of battery voltage lower.

[ionut_mtb]

Still figuring out which wax to drown the pcb in once I've thoroughly end-cleaned it.

Davor came up with parafine ideea. But never tried it. Is low dielectric and if need to work on pcb just heatup with hotair gun. Now, question is, if is to hot outside? Than what?

[ionut_mtb]

Nope, no shield - I hope that's not a "uh oh".

I went the next night to test if the annoying EMI I have on it is still there when coil is in salt water.
It was still there. So I figure it's gotta be something on the pcb. Grrrr...

The ambient temperature was 10 degrees lower this time and was notable on the decay curve or perhaps it was because of battery voltage lower.

try increase pps

[Polymer]

Davor came up with parafine ideea. But never tried it. Is low dielectric and if need to work on pcb just heatup with hotair gun. Now, question is, if is to hot outside? Than what?

Yup, no hot girls on beach allowed near detector or wax melts ... but great distraction and I wouldn't notice wax melting ...

I have looked into conformal coatings and plastic spray, but not sure if they could totally waterproof the pcb.

Making the pcb watertight is peace of mind for me, just in case that there is a leak and I don't have a fried mess inside pipe afterwards.

So I stick to snorkelling ... much better ... or perhaps not ... I shall see

[Polymer]

try increase pps

I have tried this going up to about 4.5 k pps. Same results.