Coil Detection Fields....question

Tom D. or any knowledgeable members. Is there any kind of equipment that actually shows visually the electro-magnetic field that a coil produces?
How do coil manufacturers determine what the coil is truly producing as far as a detection field goes?
For 30 yrs I have read all the coil field theories and statements. Would love to know the answers to the above 2 questions.

Computer generated models are the 'primary'......but not the real-world; however, there are field-strength meters (with software memory) that can 'model' (with 3D graph) a EMF field. There are MUCH more expenisve units that can do more......but are too rare....due to cost.

This is a link to the diagram I posted on Findmall, due to not being able to upload it here (I have pm'd Tom's webmaster on this issue)
The post is titled "Monte..what is your opinion on the accuracy of this?"

[www.findmall.com]


Would like to get opinions.

I've never seen anything as far as a REAL computer generated graph on what a coil is actually seeing ....I can only go by what I have read ......I'm sure that there would be SOME exageration to a description , but the only machine that I am considering that has a concentric coil is the CZ21 ........ Since targets are not so ganged up on the beach , it's not a bad thing to have a concentric coil on the beach .....My land machines for trashy area's are all DD coils however .....and I do agree that a smaller coil will seperate thru trash better , but I also know that I can also get pretty darn close to the depth of the larger coils with a smaller coil as I can raise the sensitivity to come very close to the depth of larger coil in trash ..... A lot of the parks that I hunt will have area's that are pretty clean , as well as trashy , so my larger DD coil stays on ..... If I plan on hitting the woods , I will put my smaller DD coil on .....Jim



Edited 1 time(s). Last edit at 02/05/2011 12:53AM by synthnut.

I saw some diagrams over on Geo forum, seems
it may have been computer generated but not sure how it was done.
That would be the forum to check out as there are a lot of techs there,
at least it was when I last visited about 2 years ago.

This is a really interesting topic. I have wondered if it is "true" that a DD coil sends down a narrow, (side to side) but broad (front to back) field. I am assuming this is at least SOMEWHAT true, as there are lots of folks on forums attesting to getting better target separation with the DD coils...

Steve



Edited 1 time(s). Last edit at 02/05/2011 05:53PM by steveg.

You can see when hitting a target that you can do the "heel " and 'toe" method of recovery when running a DD coil ..... A lot of guys use the heel and toe on the SEF coils as they have a small indentation on both the heel and toe to locate targets ..... From some of the diagrams , ( not computer generated ) they show that the center of the coil is more like a concentric coil on the SEF DD coils ....i'm not sure if all the DD coils are like this ... .... I have not seen any actual computer generated data to support what is REALLY going on ...... When I'm looking for a speaker for my audio gear or my musical instruments , I am given a complete data sheet on my speakers complete with a graph that tells me everything about the speaker .... I'm wondering why we are not privy to such information on coils that we spend plenty of money on .....?????.....Maybe we won't like what we see ? ....... It would surely make it a lot easier to pick the coil that we would like to have on our machines for a given application if we were more educated as to what the coil is actually telling us ...... Jim

I read a recent post from Monte, where he states the beam from a DD coil is actually shaped like a 'I'.

"A concentric coil puts out a cone-shaped field (shaped like a O), the DD field is more like the "center slice" of the concentric (shaped like an I)"

This intrigued me........as I had never seen/heard of the beam being shaped liked the capital letter 'I'. But I hold Monte's knowledge in very high regard. Anyone with knowledge of this beam shape?
I keep getting this intuition that the 'I' beam shape (if correct) somehow works into Tom's 'carpet of nails' results, but my mind isn't producing the hard data yet.
Darn subconcious........



Edited 3 time(s). Last edit at 02/05/2011 04:19PM by TerraDigger.

Common observation is the DD coils can pickup a signal at a shallow
distance on the outer left/right leading edge.
As the distance increases away from object, only the strip down the middle
as it is hottest.
I would suppose the field off an active detector coil would look similar to a
magnetic field.
Coil fields are on the upside as well downside.
I have always wanted a coil that didn't have a field generated off the very edges,
you know these high power units now... coil fields off the edges goes out a good
long way.
So I have wanted a coil that doesn't see very far at all beyond the edges to detect
in nail infested areas but if that field wasn't there, the coil itself probably would suffer
depth.
Back in the old days there were made I think what they called a co-axle coil, the ones
with the transmit and receive are mounted vertically.
From what I read they worked well around metal fences and the like.
I doubt we will ever see them again however.

The guy made an effort. Inaccurate, but an effort none the less.

Terra Digger (or any of you),
I propose you do an experiment and then come back here and report your findings.

Take a yardstick and lay it out on the ground. Use the 18 inch mark as your center line.
Lay a quarter at the center line. Sweep your coil parallel to to the yard stick and note and record how far the center of your coil is from the coin when you first pickup the response from the quarter (put crosshairs on your coil if you need to so you can take accurate measurements)

Then bury the coin 1" deep and repeat.
Then bury the coin 2" deep and repeat.
Then bury the coin 3" deep and repeat.
Continue progressively burying the coin an inch deeper and recording your distance until you can no longer get a response on the coin.

Graph your results.

Do it with and without headphones.

You would be quite astonished at the results if you were to put in the effort. Might even change the way you approach hunting your desired target signals.

HH
Mike