coplanar resistor location?

[grungymike]

Just read Dave Emery's article on coplanar coils, and couldn't quite figure out just where the approx 22 ohm resistor should be placed. Dave says it should be in series with the xmt coil, but should it be located on the input side of the coil, between the xmt and bucking coils, or after the bucking coil, on the ground side?

By the way, I consider this site to be worth it's weight in gold. Hopefully, in time, I'll be able to offer something other than newbie questions...

Thanx guys!

[whiskey]

Since he shows no photo or schematic for a visual. Here's one from a Russian Phazitron design. Maybe it will give you an idea or two.

[whiskey]

How's this statement for you: Dave Emery does not show a resistor because there is not one to be shown in constructing the coplanar search coil. Ask yourself, If you were to tear apart a paticular Garrett Coplanar search coil should there be any components hiding there?

Patent Drawings~Figure 2 shows capacitors used with a Garrett design. I have redlined the pics as in tearing apart a defective Garrett Coplanar...currently there are no components there at the search coil. Figure 5 should now be a more accurate view as I believe the components should already be apart of the boxed electronics.

[Qiaozhi]

How's this statement for you: Dave Emery does not show a resistor because there is not one to be shown in constructing the coplanar search coil. Ask yourself, If you were to tear apart a paticular Garrett Coplanar search coil should there be any components hiding there?

Patent Drawings~Figure 2 shows capacitors used with a Garrett design. I have redlined the pics as in tearing apart a defective Garrett Coplanar...currently there are no components there at the search coil. Figure 5 should now be a more accurate view as I believe the components should already be apart of the boxed electronics.

It probably depends on which Garrett coil you are referring to. The GTAx range do have components in the search head.

[whiskey]

Backwards Engineering At It's Best...

Qiaozhi, Thankyou. Hopefully I will be able to come across a defective GTAx search coil. More important to me is to come across a defective TDI search coil first.

Until then, Cheers

[grungymike]

resistor/capacitor?

I went back and reread Dave's article, in it he states using capacitors across the coils for a VLF design, and resistors across the coils for a PI design, which is what I'm focusing on. I think I may have misunderstood his article originally, an email I got from one of the group suggested putting the rcv coil damping resistor in the coil assy along with a trimming resistor for the xmt coil damper (working in conjunction with the main xmt damping res R11 in the control box), in order to facilitate coil swapping (especially between mono and multi) out in the field.

I don't know about Garret coils, but I've seen pictures of earlier White's coils (disassembled) which show a resistor(s) on a small PCB in the coil assy.

gm

[whiskey]

GrungyMike, the information about White’s coils is one thing that interests me greatly. Thank you! I suspected White’s designs may have a small PCB enclosed.

The Garrett coil design I tore into is for a VLF and it does not have the capacitor that Dave’s article recommends. If I were to put a capacitor in there just for general practice the detector may not function properly as designed.

I believe it is in the best favor of the coil builder to have a reference model from the original coil before a project is started. Case in point would be the TDI...while people are stating that MineLab coils are interchangeable…all manufactured coils are not necessarily designed to work with the control box settings (an example lets say, 10uS) that TDI has to offer; therefore, the detector may not function properly as designed.

It is of value for a coil builder to locate a defective original coil of the model being fabricated for and disassemble it. Get some tools an LCR and ‘go to town’.

Imagine the information that is there that was engineered into it : wire size, components, design, construction, assembly, materials, process and quality or the lack thereof. LOL.

FYI: One thing that appears to be common in old search coils is that corrosion is a possible problem. After a connection is soldered it is best to seal or encapsulate it so as to help prevent any future oxidation as well as providing strength to what may be also a smaller diameter wire. If oxidation on the coil wire develops it could lead to a reduction of the wire and breakage causing an intermittent short. The Garrett coil mentioned above had such corrosion.

Cheers, again.

[whiskey]

Ace 250 coil schematic

I was looking over the schematic forum when I came across a post by kt315 linking to a russian site. The site offered schematics with one of an ACE 250. Unfortunately, the cable was already cut off but the pcb is right there near the middle. Good pics, to bad only one side of pcb is shown.

[DOOLEY]

interesting use of 220 ohm vari pot to null the bucking coil , but then i suppose in manifacture it's quicker to twiddle a pot to null than play with a moveable loop !

very interesting in fact , had a thought , a mosfet could be used insted of the resistor , or with the resistor and the coil could be automaticaly nulled remotely either by ecu or via clever feedback so that maximum gain could be used at all times.

oh hell , if ive thought of it , someone allready tried it / done it 10 years back prob.