Use of Fluxgate Mag/Gradiometer as Boat Towed Mag??

[Robert Gecy]

Does anyone have any input on the use of the FGM-3 Fluxgate Magnetometer/Gradiometer Kit from Fat Quarters Software as a Boat Towed Mag?

http://www.fatquarterssoftware.com/Kits/Kit001.htm

It is a simple kit that works right out the box. But is it sensitive enough to be used a Mag for wreck hunting?

Thanks,
Robert Gecy



Fluxgate Mag/Gradiometer Kit

[Jan]

Re: Use of Fluxgate Mag/Gradiometer as Boat Towed Mag??

Hi,

I have some experience with these sensors.

I use 2 of them with a SCL007 chip to form the heart of a gradiometer.
Have not tested in water yet but on dry land it seems to work fine.
When I move a small weakly magnetic screwdriver near one of the sensors I see a big change on my computerscreen.
When I switch Gain on (SCL007) then the graph shoots to maximum.

I cannot garantee that it will find every scrap of metal but I would be quite supprised if it would not find large chunks of metal... like shipwrecks.

But as I said, I have not tested it underwater.

Hope this helps.
Jan

[Francisco Xavier]

Re: Use of Fluxgate Mag/Gradiometer as Boat Towed Mag??

Hi subcribers,
Last year I assembled a dif.mag using two FGM3-h (hight sensitivity apx.2x) without SCL007. For that I design a board using two schmit triggers and two digital frequence subtractors (70..) and have good results on a static base (one ton car at 20 meters) the frequence shift a litle on first 30 minutes (worming sensors), but after is very stable.
The problem I never could align the sensors and make the frequence dif equal zero and spining the 1.7 PVC/Aluminium tube the frequence shifts about 100 Hz (~_ 80 gama). I test it on the water and have the same shift. This superimpose any weak field I could test.
The Fluxgate problem is uniquely the directional
response.
Best regards to all and spetialy to Carl to implement this forum again.
Francisco Xavier

[Carl]

Re: Use of Fluxgate Mag/Gradiometer as Boat Towed Mag??

Robert,

I got your email, sorry for not getting back sooner.

Everything I've heard suggests that proton mags are more sensitive, but making the sensors is a real chore. I think with some care the fluxgate mag can be used for wreck hunting.

In normal sensitivity mode it has OK range and, as Jan says, in 10x mode it just rails out. This is entirely due to minute misalignment in the sensors, so if you can (a) do a super job aligning the sensors or (b) add a nulling coil to the whole setup (sort of a motion magnetometer) then I think it would be a decent wreck finder.

I got a special version of the SCL007 chip in which the max sensitivity mode has been reduced somewhat. It was still too sensitive for my mechanical setup so I've made a more stable setup, but have not yet tested it.

Then, you would need to build a fish, for which a lot of info has be posted in the Side Scan forum.

- Carl

[Jan]

Re: Use of Fluxgate Mag/Gradiometer as Boat Towed Mag??

Carl,

When I set gain on, the trace stays more or less at the centerline, only when I move the screwdriver near one of the sensors I get a huge reading.

If you like I could send you all my schematics, PCB layouts and programs so you could post them here.
There is still some work to be done, but the basic Magnetomer is working.... in a simple way.
I think it works good enough for people to play with it.... as long they do not expect a commercial grade program and looks.

Jan