How much difference

[sportscanuser]

How much difference is there in the detection range of a fluxgate unit like the one in the EPE article and a the best unit you can buy .like if you were searching for a large sub in 40 meters of water how close would you have to get to detect if with each unit. I am thinking of building the EPE unit but dont want to be wasteing my time, so could some body give me the approx range on metal targets of say 10kg,100,kg,10,000kg and 10,000,000kgs between each unit

[DiveExplorer]

I was also wondering about this.

I recently built Carl Moreland Fluxgate FGM-3 and it´s up and running. I have only tested it on land and it´s working fine but I have to say I was little disappointed about it´s range. The distance between the sensors may be to short, only 50 sm, but I don´t know if that's the case. And I´m towing it horizontal. But it was only measuring metal, like my car from only 3 to 4 meters. Is that normal?

The good thing about it when it came to contact, near metal, it was a "clear" sound (if you know what I mean).

I´m going to construct towfish so I can tow it behind my boat. That work is in process.

I have also bought EPE magazine and it´s magnetometer board, and maybe I will construct it to.

[Carl-NC]

Regrettably, fluxgate mags are not as sensitive as a good PPM, but they are far easier to build. I suspect there are ways to improve the FGM-3 sensitivity, but I have no time to work on it.

- Carl

[DiveExplorer]

As I see it this design is very good to build. It´s relativity ease and you get most of the components in the mail. It´s also good starter kit in the world of magnetometers and for some the only kit they need.

Question to those who have built and test it, do you get the same sensitivity as I got (signal from a car in 3-4 m distance, around 10 - 20 feet) (40 feet container near 6 m, 20 to 25 feet) or is there something in my design I could do better?

[Geophyz]

The main thing you need to remember when building fluxgate gradiometer is the alignment of the two sensors. The two sensors must be precisely aligned. If the sensors are not aligned properly, the magnetometer will be less sensitive and MORE prone to directional error.

With that said, the EPE magnetometer logger is a 1nT instrument. It logs in 1nT increments. Most of the old PPM were also 1nT instruments. A good commercial fluxgate mag (Geoscan or Bartington or Forster) are typically 0.1nT (or better) instruments. A typical cesium mag is 0.01nT or better. So we are really talking orders of magnitude here.

1nT = EPE, Old Proton mags

0.1nT= European fluxgate gradiometers (Geoscan etc...), Newer Proton Mags like overhauser

0.01nT (or better)= Cesium, Potassium

A 1nT instrument will have NO PROBLEM detecting a sub in 40 meters of water. The old 1nT PPM's found many a shipwrecks. Just make sure the fluxgate sensors are properly aligned.

[sportscanuser]

what difference a order of magnitude

Can you clarify what difference a order of magnitude means to sensitivity ,
like can a unit be to sensitive for practical use ,so once again can you estimate how far each of the below will detect a cannon ball and a large item like a sub
1nT = EPE, Old Proton mags cannon ball X meters large sub X meters

0.1nT= European fluxgate gradiometers (Geoscan etc...), Newer Proton Mags like overhauser cannon ball X meters large sub X meters


0.01nT (or better)= Cesium, Potassium cannon ball X meters large sub X meters

thanks in advance

[Geophyz]

Can you clarify what difference a order of magnitude means to sensitivity ,
like can a unit be to sensitive for practical use ,so once again can you estimate how far each of the below will detect a cannon ball and a large item like a sub
1nT = EPE, Old Proton mags cannon ball X meters large sub X meters

0.1nT= European fluxgate gradiometers (Geoscan etc...), Newer Proton Mags like overhauser cannon ball X meters large sub X meters


0.01nT (or better)= Cesium, Potassium cannon ball X meters large sub X meters

thanks in advance

I would not know these types of numbers off hand. Your best bet is to download some forward model software for magnetics and figure out how large (amplitude) your anomalies would be for those targets. Download the free version of Potent called Pblock and have fun making your models. Like I said earlier, a 1nT instrument should be good to find those large iron objects.

http://www.geoss.com.au/Potent_downloads.htm

Anothe rforward model software MagCad (free) can be found here.
http://www.umt.edu/geosciences/facul...f_software.htm

Good luck

[Geophyz]

Can you clarify what difference a order of magnitude means to sensitivity ,
like can a unit be to sensitive for practical use ,so once again can you estimate how far each of the below will detect a cannon ball and a large item like a sub
1nT = EPE, Old Proton mags cannon ball X meters large sub X meters

0.1nT= European fluxgate gradiometers (Geoscan etc...), Newer Proton Mags like overhauser cannon ball X meters large sub X meters


0.01nT (or better)= Cesium, Potassium cannon ball X meters large sub X meters

thanks in advance

found this at the ELSEC website. http://www.elsec.co.uk/7706.htm

The distance at which a ferrous object can be detected is naturally dependant upon a number of variables such as weight, shape, orientation etc. For example a 5,000 tonne mass of of iron could be detected at up to 500 meters (nearly ½ a mile), a 1 meter diameter pipeline could be detected at 100 meters. The following diagrams show detection distances for various objects based on a 5nT anomaly. (The 7706 is sensitive to 1nT but 5nT makes the it easily distinguishable from random background variations).