Magnetometer/PI combo

[Darren in NC]

If you saw the Ferrous Hound at:

http://www.reevejones.com.au/product.html

Is it possible to develop something along this lines for shipwrecks? It would be great to have a PI to get hits, but then see if the mag was hitting simultaneously. If so, then you can assume a ferrous hit. If not, then you can assume a non-ferrous hit. It would be a roundabout way to get discrimination with a PI. Carl said he thinks it's possible. Anyone ever try something along these lines?

Darren

[bakergeol]

Yes Carl is correct. I own a Ferrous Hound which is mounted in the center of my 11" mono coil for my new Goldscan 5.

There are no problems if you plan to turn off the PI and engage FH-(desert gold hunting- 6 iron hits per day). However, in high trash areas which you plan on running the PI and mag together you may have problems.

Running the PI and FH at the same time with mono coils. Small mono coils usually create too much interference for the FH to be run at the same time. A 9x5" ellip. nuggetfinder coil with my GS5 could not be run at the same time with the FH. However, Eric Foster's 6" mono could be run if the sensor was more than 1 1/2" from the coil. Usually large mono coils can be run at the same time with the FH. A Coiltek 14" mono could be run at the same time with the FH.

Running the PI and FH at the same time with DD coils. This is the preferred method in Australia. You mount the FH sensor on the transmit side of the DD coil.

My GS 5/FH combo. I had my FH modified to accept a headphone jack. The original model just had a buzzer. My GS 5 is hip mounted with a separate shaft for the coil. I mounted a LED meter on the shaft(hooked up to the headphone jack). I also obtained a larger rechargeable battery. The Ferrous Hound sensor is mounted directly in the center of the 11" coil. So I just turn both on and when I sweep an iron object the GS 5 will give me a low tone(iron) and the LED mag meter will light up at the same time. As long as you keep the FH sensor at least 1" away from the coil- the FH will not receive any interference. I have not taken it into the field yet so I don't know how much(any?) feedback the FH wil give the GS 5.

The GS 5 has a new iron ID system but it has limitations, The GS 5 is so new that only a handfull are out there. I have a long way to go to learn this machine.The FH has limitations too- if you want to know more -just ask. It is hoped that this combo would give the best iron ID ability out there for a PI .

George

[Darren in NC]

Wow, George, thanks for the info. I hope someone can use that to help them in the field.

I was hoping to apply the mag idea to a pulse induction unit with a large coil embedded in the hull of a boat. The idea is to be able to detect nonferrous shipwreck cargo. Of course a pi picks up all metal. So the mag would hit simultaneously to indicate a ferrous target. If the mag didn't hit, but the pi did, them it could be assumed that the target was non-ferrous. Of course, the sensors would have to be scanning the identical area as the pi loop.

Any ideas?

[Ferric Toes]

Something I had always dreamed of trying, resulting in an ideal Fe/Non-Fe discriminator. I had done tests with a simple fluxgate arrangement, but at the time, could not get the sensitivity sufficiently good to signal small ferrous items e.g. less than a 1in nail. If the Ferrous Hound does that, then it opens up new possibilities.

I would imagine that it is a gradiometer type sensor arrangement, and that it works well with my coils because you can position the sensor in the open centre, such that their is little or no mutual coupling either way. The only problem I can see, is that the pinpointing of the target on the mag. would not correspond to the PI detector. It may be better if the mag sensor were aligned in the direction of the coil sweep. Perhaps George could comment on this.

I remember once seeing a constructional feature for an induction balance metal detector, in which the receive coil was a wound ferrite rod positioned horizontally in the centre of a normal circular TX coil. Again there was a point where the coupling was zero, until a metal target distorted the field. I wonder if anyone else has come across, or used, this technique.

A boat mounted system is a different ball game, and if the FH is a gradiometer, then the sensor spacing would be too small to detect magnetic anomalies at a distance. One would need to know more about the depth of water in which it is proposed working and the size of Fe/Non-Fe targets that are expected. Best idea is to tow a sled with the PI and Mag sensors on, and have most of the electronics in the boat. I have run PI's with up to 300ft of cable between the electronics and the coil. You have to run at a long sample delay, because of all that extra capacitance, but if you are looking for bronze cannon, or silver bars, it doesn't matter.

Eric F.

[bakergeol]

Hi Eric

Regarding the alignment of the FH sensor in the coil it doesn't make any difference. The sensor detects in a multi-directional field. It is like putting the sensor in the middle of a soccer ball. As an iron object penetrates the soccer ball it is detected. There are no weak signals as it is detected or it is not. However, there is a preferred direction in which the sensor needs to be pointed for the deepest depth. For me this is the NW. So for maximun depth I have to remember to detect toward the SW or west. Regarding the pinpointing I just have to see on my field tests. I will also be looking at the interference the mag has for the GS5

Regarding it's depth-Yes the Ferrous Hound is more sensitive to smaller iron objects than conventional utility locators. However, it's depths are far below what a good PI can give you.

Quarter size paper thin rusted iron = 3"
1/4" nut = 4"
bottle cap = 5"-6 1/2"
1" dia steel washer = 6 1/2"
nail 1 3/4"longx5/16" = 9"
1/4" bolt 1" long = 11"
nail 1 3/4" long X 1/2"= 12 1/2"
can crushed = 16"
can whole = 21"
hot rock 2"X1" = 20"

You will notice the weakness mags have for thin, flat iron. The better the shape the deeper the depth. Notice the mag loves hot rocks because of their great shape.

In short I have never regarded the mag as the final solution with a PI because of it's weakness toward thin flat iron. However, combined with a PI like the GS5 which has an iron ID ability perhaps they could compliment each other on their weak points.E.G- the mag could indicate "hardened steel" high tones and the GS5 would give me a handle on deep iron.

George