Menu
What's new
Find's Treasure Forums

Welcome to Find's Treasure Forums, Guests!

You are viewing this forums as a guest which limits you to read only status.

Only registered members may post stories, questions, classifieds, reply to other posts, contact other members using built in messaging and use many other features found on these forums.

Why not register and join us today? It's free! (We don't share your email addresses with anyone.) We keep email addresses of our users to protect them and others from bad people posting things they shouldn't.

Click here to register!

Need Support Help?

Cannot log in?, click here to have new password emailed to you

PI coil questions

A

Anonymous

Guest
I've become interested in PI machines and have some questions about coils and the field shapes they produce.It appears there are two types, the monoloop and the widescan. I'm wondering if the monoloop field is concentric and the widescan is bowl shaped.Also can any PI use either one if available(eg Sandshark, Minelab SD series)? Finally since the widescan has much greater coverage, works better under highly mineralized conditions, and supposedly only loses a tiny amount of depth I'm wondering why more are not in use. Of the detectors I've seen so far only the Tesoro and Minelab use them. Thanks, Eric
 
I'm no expert Eric but I think you're right on as far as your conclusions. Yes, a widescan (or "DoubleD") coil could be used on any PI if they matched inductance-wise and electrically. I think one of the reasons why they're not used more is that DoubleD coils apparently are not quite as sensitive to smaller objects as a mono coil.
I'm sure Eric and Bill can give more specifics or call me a liar, but I think for the most part you're right on target... <IMG SRC="/forums/images/biggrin.gif" BORDER=0 ALT=":D">
-J
 
Eric,
With a PI the "monoloop" has only one winding so it's not really called concentric, which refers to a coil with two windings. A PI detector has to be specifically designed for a widescan coil because of the two loops vs one... my Sandshark, for example, cannot accept a widescan.
I think the reason widescan coils are not used as much with PI is because the RX circuitry is a little harder, and I don't think it buys you much. I believe what you said about it working better in mineralized soil is valid for IB detectors, not so sure about PI.
 
Hi Eric and all,
Concentric and Widescan are terms that originated with induction balance type detectors. A concentric coil arrangement usually consists of an outer transmitter coil with and inner receiver winding which may only be half the diameter. The problem with this, is that although the overall coil diameter is, say, 10in, the sensitive receiver area is only half that, giving a very sharp narrow response from any direction. Enter the widescan DD type coil. Here, each coil is the same physical size but overlapped like two D
 
Eric, If I understand about concentric coils that the Rx coil is half the diameter of the Tx coil? Is it possible to explain alittle more on the topic of contruction of a concentric coil? I know of others that would like this explained to a better understanding of the beast. Also, It seems that the Rx coil on the inside of it is a coil in series with the Tx coil. Is this to help conceal unwanted noise? Any help would be greatly appreciated. Rick S
 
Hi Rick,
Concentric coils vary in their construction but a popular type consists of an outer TX winding with an inner RX winding of about half the diameter of the TX. In addition the RX winding has a few turns which, as you say, are in series with the TX. The purpose of this winding is to give an antiphase signal to balance out the direct TX induction in the main RX winding. Also there is often a loop of wire, again in series with the TX, whose position is adjusted on test (then glued down)to give an accurate cancellation, or balance. Hence the term, Induction Balance, for a detector with this type of coil arrangement.
Eric.
 
Concentric coils have been used on PI's. but the balancing winding is not needed. This is because the receiver reads the signal in the off time of the transmitter when there is no direct induction. The benefit again is a greatly reduced ground signal.
Eric.
 
Hi Eric,
just for better understanding - assuming a DD coil arangement, with 3:1 sides ratio, overlaping done on the long sides. You say, there is a detection range improvement if compared to DD-coil with (I suppose) square coils. Do you assume the short side to be equal to one side of the square coils for that comparision, or the long side? Can you figure out, how much improvement could be expected?
Thank you
Walter
 
Eric have you done any tests with co-axial coils on PI detectors ? I have found them to be very stable on my old VLF in high electrical interference areas I think there are three coils one TX and two RX may be you only need two on a PI are they as stable as DDs in hot ground?
Regards
Chris
i
 
Hi Chris,
There are two types of coaxial coil. Coaxial/Coplanar where all two or three coils are inside one another and in the same plane. The other type is with the three coils stacked vertically. TX is usually in the middle with RX either side and connected in opposition. This type gives very good noise rejection due to noise being picked up equally on both loops. Metal signal is obviously much stronger on the bottom coil. You can use just two stacked coils on a PI. The bottom one is TX/RX1 and the top one RX2 and, again, connected in opposition to cancel noise.
Eric.
 
You must log in or register to reply here.
Top