Does Target orientation affect discrimination

[James O]

Hi, all

How does the orientation of a coin or other target affect the coupling between the TX and RX coils?

[Reg]

Hi James,

Yes, target orientation does make a difference but it normally doesn't become obvious until the target is some distance away from the coil.

The problem isn't so much the orientation per se, but the amount of the target "visible" to the coil. Then it is just how this signal relates to the ground signal. The result is a very weak signal will have a tendency to read differently, normally higher than normal. George Payne discussed this in one of his posts on another forum. Here is the link to that forum:

http://members5.boardhost.com/MetalD...html?993517102

I think this link will take you to the info but not sure:
http://jb-ms.com/Baron/


Any other target within the range of the coil at the time of target sampling will have some influence. In this case, it is more of just how the target evaluation is done and how close the object is as to how much influence a second object has.

Different manufacturers use different techniques as to how they evaluate a target. Some will average a signal, others will sample at a peak signal, and others may use slightly different technques. Now, depending upon the technique used will determine how a nearby target can influence the signal.

I hope this helps.

[Reg]

Hi Again James,

Sorry, the post by George Payne was more of one on target signal strength and ground signal. However, the same concept does apply since orientation will determine target signal strength, thus will affect TID, especially if deep.

Here is a link to a discussion about why TID can read high. Basically, it has to do with the strength of the target signal in relation to the ground signal.

http://www.fortunecity.com/marina/st...Oct5/8946.html

Reg

[James O]

Thanks Reg

Much appreciate your response to my question. I didn't know of the existence of the other forum and will enjoy reading through the archives. I'm affraid your explanation went a little over my head as i'm not familiar with modern MD's - i'm just trying to build a simple VLF. I have noticed that when i have a copper coin oreintated in the same plane as the coils, the recieved signal amplitude increases, but if i turn the coin so it's a perpendicular to the coils the signal amplitude decreases, and wondered if this can be the basis of some sort of simple discrimination.
Many thanks again for taking the time to reply, all the best, James O

[Reg]

Hi James,

Sorry if the info was a little too technical. Just for your information, some of the discussions on the other forums are written by George Payne, one of the truly great design engineers responsible for the VLF's as we know them today.

George designed the first consumer VLF, the first VLF motion discriminating detector, the first TID machine, the first with audio ID, the first with surface blanking, the first with notch, and a few others that I have forgotten.

The point is, when George writes something, you be assured the knows what he is talking about.

Reg