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Best settings for finding large iron objects
Posted by: Overvoltage
Date: September 07, 2017 01:38PM
Hi all, I have been lucky enough to be recruited by a historical society team that is looking to find a section of historical, abandoned railroad tracks from the 1830's. I say lucky because the section of railroad is of significant historical value as its construction was an example of the very first railroads in America, and it is in a protected wilderness area that the team has been granted permission to search in. I even have park rangers doing the digging for me (its going to spoil me). The rails have been abandoned for about 170 years. It is in a section of woods that is mostly loose sandy soil and leaf decomposition. We have LIDAR mapping data that somewhat shows where we think the roadbed was and the historical society says the tracks were not removed as far as they know. I have been able to detect a lot of spikes so I know we are in the right area. However, I have not been able to detect any rail at all. I am using a completely open screen, deep on, fast off, seawater on, low trash, pinpoint normal. I did find a piece of big heavy iron, same thickness as the track, that was most likely a spacer for the track and it hit like I thought it would, bottom right of the screen, 36-47 and then overload. I figured large 15ft lengths of track would be easy to locate but that hasn't been the case. We know the track has been covered by sand and soil from erosion as the early documentation of this section of roadway stats that sand had to be continuously removed from the tracks when it was in operation. So, based on this, am I using the right settings and how deep can I expect the CTX3030 to detect big iron such as rails? Could they be just out of detecting range? I suspect they are probably about 3-6ft deep. I do have a pulse induction machine (Infinium LS) but with the amount of smaller iron targets it might not be effective until we clear the area of all smaller targets. Any suggestions?

Re: Best settings for finding large iron objects
Posted by: jojames2
Date: September 07, 2017 03:25PM
Rent a metal detector that a land surveyor would use.
They are set up to find such items only.
Schonstedt Magnetic Locator

Re: Best settings for finding large iron objects
Posted by: brother steve
Date: September 07, 2017 03:30PM
Borrow or buy a GPX 5000 or 7000.

Re: Best settings for finding large iron objects
Posted by: trojdor
Date: September 07, 2017 03:37PM
You didn't mention which coil you're using. I'd recommend the 17".
Always match you coil size to target size...big target, big coil...small target, small coil.

You're settings look fine/optimal to me. The only thing I'd change is switching pinpoint normal to pinpoint sizing...you'll definitely want to be able to hear the size and shape of your signals.

It's possible...if the rails are really 6' deep...that you'll need to switch to the PI machine.
I think 3' is probably do-able on the CTX, depending on the mass of the rail, but I suspect 6' is well outside of detection range. (Induction field strength drops off exponentially.)
If I had some railroad/rail sections lying around, I'd be been glad to test it for you.

Small targets shouldn't fool you (with either machine). A 15' long section of track should be obviously different sounding than a tin can, for instance.
Don't think so much in terms of pinpointing, but in using pinpoint to 'paint' the size and shape of the target in your mind as you sweep and hear the audio.
(Sort of a poor man's GPR.)

It's always possible you simply haven't gotten over the target yet?

Regardless, it sounds like a fun gig!
Good luck, and have fun,
:)
mike

EDIT:
One other thing I thought of, is the possibility that at some point in time, someone may have (illegally) pulled up sections of the track for sell for scrap iron?
(Especially if you're finding lot's of spikes...but no rail.)
Our economy has certainly gone through some tough times since the 1800's....perhaps making that an appealing option at some point to some people.



Edited 3 time(s). Last edit at 09/07/2017 03:51PM by trojdor.

Re: Best settings for finding large iron objects
Posted by: bklein
Date: September 07, 2017 06:52PM
I have been buying and repairing magnetic locators like the GA-52cx. They definitely are what you should use.
Get one off eBay or trade me something cool for one. Doesn't have to work...

Re: Best settings for finding large iron objects
Posted by: sharkbait
Date: September 10, 2017 10:48PM
Paul, the tracks are probably still there but there is also the possibility that they were acquired for scrap since there were drives for WW1 and WW2. Hitchcock woods wasn't a protected area then and of course the locals knew that these existed. Just throwing this out there as a possible explanation. I hope you do find them. Tim

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Re: Best settings for finding large iron objects
Posted by: Overvoltage
Date: September 13, 2017 02:42PM
We have found portions of the track in the sand river which would have been easy picking if it had been pillaged for scrap. I had the 9" coil on but have since put on the 17" and changed PP to sizing but we haven't had the chance to get back out there since the storm hit. I plan on doing an air test on the rails we have found to see what the detectable distance is. I also have a Garrett Infinium LS that I have put the 10X14 coil on as well.
As far as the small targets go, They haven't fooled me as I know they are smaller targets other than my concern that they may be masking such a deep target.
Sharkbait, you must be local to my area.



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