Question on coils
- Thread starter John 71
- Start date
Jason in Enid
Elite Member
Concentrics are slightly deeper, but that deepest portion is only very small spot under the center of the coil. Think of a cone from the full coil size down to that point, and thats basically your response zone for coin sized objects.
A DD coil isnt quite as deep, but it gets basically full depth from front to back down the center of the coil.
So for the deepest targets, one is like searching with a 1" coil, the other is like 8, 9, 10, etc inches.
There are also other benefits but thats a longer discussion.
Monte
"In Memory of"
Sometimes there can be a difference in performance based upon the particular make/model detector and how a particular search coil was designed.John 71: said:
That said, if two search coils are of the same or very similar physical size, the 'edge' in depth goes to the Concentric coil. Both a Concentric coil and Double-D designed coil will 'pinpoint' at their deepest depth at the center-axis of the search coil's EMF. That is because the reactive portion of both design types will taper as the coil-to-target distance increases.
A Concentric coil's EMF will be wider near the coil and taper gradually near the upper two or three inches and then the reactive portion tapers more quickly and a side view will appear more like a funnel shape but not quite a pronounced 'V' pattern. The Concentric coils EMF will be more uniform shaped from any approach of the search coil.
A Double-D type coil has a reactive FMF more from the center line, front-to-rear, of the search coil, and if viewed from the side the reactive portion of the field is more bowl-shaped but the deeper response area will still be near the center axis of the search coil.
But that is just trying to interpret depth-of-detection between two similar-size coil types. There are other differences in their detection behavior. Due to the more uniform placement of the Tx and Rx internal windings, a Concentric coil will respond similarly regardless of the search coils approach to a metal target. But the Double-D's overlapping of the two inner windings does create some differences in behavior.
As the coil is swept one direction the leading edge of the coil will have the Tx winding, then the overlapped portion down the center-line of the coil, and then the coil is swept past the metal object through the Rx winding. Yet when swept from the opposite direction the metal object will be encountering the Rx field first, then the overlapped reactive portion, then exits through the Tx side of the field.
Therefore, between the two coil winding designs, that can cause some differences in both the Audio or Tone ID response as well as any Visual Target ID response. More often than not it will cause the Double-D coil to be less accurate or not have as tight a numeric VDI read-out as a Concentric designed coil.
Also, a Concentric coil design usually does a much better job when dealing with iron and other ferrous or magnetic metal objects resulting in better ferrous object Discrimination. All of these things need to be considered rather than only focusing on detection depth.
I have used both types of search coils for many decades, and today my search coil preferences are mainly determined by the particular make-and-model detector sI am using as well as the application and site challenges. Some models, such as my Nokta FORS CoRe devices ,only have Double-D search coils available so my pick is limited to that type. My White's XLT only has Concentric coils for it in my outfit, and the same for my Classic ID or Tesoro Bandido II µMAX or Silver Sabre µMAX.
But other models offer both search coil types, like the Nokta /Makro FORS Relic, Impact, Anfibio, Racer 2 and Multi-Kruzer, White's MX-7 and Teknetics Omega 8000. This group gives me the option to select different coil types to best handle different search applications, and that's what I did in outfitting each model in my Regular-Use Detector Team with the coil size and type that I am going to use most often.
I'm not sure which detector model you are using or the types of sites and challenges you face, but there are some answers and a few comments that might be of help that are based on over half-a-century of in-the-field experience.
Monte
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