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Okay, I have a Whites Coinmaster V Supreme, which uses a 4BDM coil, and since Ivconic and others made a Coinmaster 3900/D board, they must have made a coil for it. I believe it also uses a 4BDM coil????
Here is what Whites says about that 4BDM coil:
Here is what Whites says about that 4BDM coil:
Balanced search loop for metal detector
A search loop for a metal detector is described having a magnetic flux feedback coil whose magnetic flux opposes that of the transmit coil to provide a balanced loop. The balanced loop is thereby nulled and produces no output signal on the receive coil when such loop is positioned in air remote from the ground and no metal object is present. The transmit coil, the feedback coil and the receive coil are supported coplanar with each other and the feedback coil is supported on the receive coil so that it is concentric therewith. As a result of supporting the feedback coil on the receive coil, there is no relative movement between these two coils due to temperature changes or mechanical stress. Such movement tends to produce false output signals in the receive coil. In the preferred embodiment the feedback coil and the transmit coil are circular and are positioned concentric with a surrounding circular transmit coil. In one embodiment an electrostatic shield is provided between the feedback coil and the receive coil to reduce capacitive coupling. The balanced loop of the present invention can provide a balanced magnetic flux region within the receive coil even though it is not exactly concentric with the transmit coil so the loop is less expensive to manufacture but is capable of high sensitivity and good pinpointing of a target.
Then Whites gives the technical information about the actual coils:
DESCRIPTION OF PREFERRED EMBODIMENT
As shown in FIG. 1, a search loop 10 made in accordance with the present invention is attached to a support rod 12 of a metal detector by a pivot pin connection 14 and is electrically connected to the metal detector circuit by a cable 16. The search loop includes a plastic housing 18 which has been removed in FIG. 2 to show the coils of the search loop contained therein. The balanced search loop of the present invention includes a transmit coil 20, a receive coil 22, and a magnetic flux feedback coil 24, which are supported coplanar to one another by the housing 18.
As shown in FIG. 3, the feedback coil 24 is supported on the receive coil 22 throughout at least a major portion of its length by wrapping the turns of the feedback coil on the outside turns of the receive coil. In the preferred embodiment, the transmit coil 20, the receive coil 22, and the feedback coil 24 are all circular and are positioned concentric to one another so that they are all centered on a common central axis 26. However, it is possible that the unit formed by the receive coil 22 and the feedback coil 24 may be positioned somewhat off center from the axis 26 of the transmit coil and still give good results. Thus, magnetic flux 28 produced by the magnetic feedback coil 24 will cancel magnetic flux 30 of the transmit coil 18 in a balanced region 32 bounded by the receive coil 22 to null the output voltage of the receive coil 22 to substantially zero when the loop is positioned in air remote from the ground and any metal object. The balance region 32 can be produced even when the receive coil and feedback coil unit is moved somewhat off center from the central axis 26 of the transmit coil. This is important because it enables less expensive manufacturing of the balance search loop of the present invention since it does not require manual positioning adjustment and mounting of the receive coil exactly at the center of the transmit coil.
As shown in FIG. 4, each of the turns 34 of the receive coil 22 and each of the turns 36 of the feedback coil 24 are bonded together by the synthetic plastic insulating material provided over the metal wires forming such turns. This may be accomplished by means of so called "self-bonding wire" in which the insulation coating on such wire bonds together upon heating or upon immersion in a chemical solvent in a conventional manner. Under some conditions it may be necessary to reduce the capacitive coupling between the feedback coil and the receive coil by providing an electrostatic shield 37 between such coils, as shown in FIG. 4A. The shield may be a layer of metal foil wrapped over the outermost turns of the receive coil 22 before the turns of the feedback coil 24 are wrapped onto such receive coil. Of course, a conventional Faraday shield (not shown) may also be employed inside the bottom of the loop housing 18. Both shields are connected to D.C. ground potential by a conductor in Cable 16.
As shown in FIG. 2 a tuning coil 38 consisting of a portion of one turn of wire is connected between the output end of transmit coil 20 and the input end of feedback coil 24 for fine tuning the null balance condition. Thus, the position of the partial turn forming tuning coil 38 is adjusted until a minimum output voltage or null condition is achieved at the output of the receive coil 22. Null balancing of the search loop is achieved because while the transmit coil 20 and feedback coil 24 are connected in series through tuning coil 38, such transmit coil and feedback coil are wound in opposite directions to produce signal voltages of opposite polarity across such coils as indicated by the polarity dots at top and bottom of coils 20 and 24 in FIG. 5. Then the tuning coil is fixed in position by adhesive tape or other means prior to permanent bonding it to a loop housing insert 35 of plastic foam such as polystyrene foam during manufacture. For purposes of clarity the foam insert 35 has been removed from FIG. 3. The input end of the transmit coil 20 is connected by an electrical lead 39 in cable 16 to an oscillator 46 in the metal detector circuit. In a similar manner, the output end of the feedback loop 24 is connected by another electrical lead 41 thru cable 16 to ground or to the other output of the oscillator when a push pull rather than single ended output is provided by such oscillator. A capacitor 40 is connected between leads 39 and 41 across the series connection of coils 20, 38, and 24. In the one embodiment with an oscillator frequency of between 5,110 Hz and 5,140 Hz, the capacitor 40 has a value of 0.33 microfarads and may be a polycarbonate capacitor with a tolerance of .+-.5%. A second capacitor at 42 may be connected in parallel with capacitor 40 to tune the oscillator output signal to 5,125 Hz. In this case, the second capacitor 42 has the selected value which is necessary to provide the oscillator frequency of 5,125 Hz. The output terminals of the receive coil 22 are connected by leads 43 and 45 thru the cable 16 to the receive signal input of a metal detector circuit 48. A third capacitor 44 of a value of 0.027 microfarads similar in type to capacitor 42, is connected between the output leads 43 and 45 across the receive coil.
As shown in FIG. 5 the oscillator 46 is of a single ended output type which has one output connected to the input lead 39 of the transmit coil 20 and has another output connected thru lead 47 to the metal detector circuit 48 to provide a reference signal. The metal detector circuit may be of any suitable type such as the metal detector shown in the patent application Ser. No. 875,677 filed Nov. 6, 1978, by James P. Karbowski. Thus the receive signal produced on the output leads 43 and 45 of the receive coil is transmitted as the input to the metal detector circuit 48 and processed to indicate whether a metal object is present in the electromagnetic field of the transmit coil 20.
As shown in FIG. 2, a grounded lead 50 is provided in the cable 16 for connection to a Faraday shield (not shown) or to the electrostatic shield 37 of FIG. 4A.
In one preferred embodiment of the present invention, the loop housing 18 was provided with a diameter of approximately 8" and contained a transmit coil of eighty five turns of No. 27 self-bonding wire. The inner diameter of the transmit coil was 6.375 inches while its thickness or height was 0.188 inches. The receive coil 22 was provided by 275 turns of No. 31 self-bonding wire and had an inner diameter of 3.188 inches and a thickness or height of 0.219 inches. The feedback coil 24 was provided by 27 turns of No. 31 self-bonding wire wrapped on the outside of the receive coil. After winding the coils were mounted in the foam core 35 and glued in place with wood glue. After nulling, the receive coil output under balanced conditions is less than 6 millivolts peak to peak amplitude and has a lead phase difference relative to the transmit signal of 40 to 100 degrees.
Now my questions. I have never made a coil myself, and do not know what connector is used for this coil, where to purchase this connector, and how to actually make this coil. If I cannot find these wires, or the wire sizes, what would I use in their place as a substitute? I would like to make a small coil, such as around 3" or 4", for gold nugget searching, and a larger coil, such as 12" or 14" or 16", for deep searching. What should I do for those sizes? Any suggestiongs? Thanks for reading and for helping, if you actually do post to help me.
As shown in FIG. 1, a search loop 10 made in accordance with the present invention is attached to a support rod 12 of a metal detector by a pivot pin connection 14 and is electrically connected to the metal detector circuit by a cable 16. The search loop includes a plastic housing 18 which has been removed in FIG. 2 to show the coils of the search loop contained therein. The balanced search loop of the present invention includes a transmit coil 20, a receive coil 22, and a magnetic flux feedback coil 24, which are supported coplanar to one another by the housing 18.
As shown in FIG. 3, the feedback coil 24 is supported on the receive coil 22 throughout at least a major portion of its length by wrapping the turns of the feedback coil on the outside turns of the receive coil. In the preferred embodiment, the transmit coil 20, the receive coil 22, and the feedback coil 24 are all circular and are positioned concentric to one another so that they are all centered on a common central axis 26. However, it is possible that the unit formed by the receive coil 22 and the feedback coil 24 may be positioned somewhat off center from the axis 26 of the transmit coil and still give good results. Thus, magnetic flux 28 produced by the magnetic feedback coil 24 will cancel magnetic flux 30 of the transmit coil 18 in a balanced region 32 bounded by the receive coil 22 to null the output voltage of the receive coil 22 to substantially zero when the loop is positioned in air remote from the ground and any metal object. The balance region 32 can be produced even when the receive coil and feedback coil unit is moved somewhat off center from the central axis 26 of the transmit coil. This is important because it enables less expensive manufacturing of the balance search loop of the present invention since it does not require manual positioning adjustment and mounting of the receive coil exactly at the center of the transmit coil.
As shown in FIG. 4, each of the turns 34 of the receive coil 22 and each of the turns 36 of the feedback coil 24 are bonded together by the synthetic plastic insulating material provided over the metal wires forming such turns. This may be accomplished by means of so called "self-bonding wire" in which the insulation coating on such wire bonds together upon heating or upon immersion in a chemical solvent in a conventional manner. Under some conditions it may be necessary to reduce the capacitive coupling between the feedback coil and the receive coil by providing an electrostatic shield 37 between such coils, as shown in FIG. 4A. The shield may be a layer of metal foil wrapped over the outermost turns of the receive coil 22 before the turns of the feedback coil 24 are wrapped onto such receive coil. Of course, a conventional Faraday shield (not shown) may also be employed inside the bottom of the loop housing 18. Both shields are connected to D.C. ground potential by a conductor in Cable 16.
As shown in FIG. 2 a tuning coil 38 consisting of a portion of one turn of wire is connected between the output end of transmit coil 20 and the input end of feedback coil 24 for fine tuning the null balance condition. Thus, the position of the partial turn forming tuning coil 38 is adjusted until a minimum output voltage or null condition is achieved at the output of the receive coil 22. Null balancing of the search loop is achieved because while the transmit coil 20 and feedback coil 24 are connected in series through tuning coil 38, such transmit coil and feedback coil are wound in opposite directions to produce signal voltages of opposite polarity across such coils as indicated by the polarity dots at top and bottom of coils 20 and 24 in FIG. 5. Then the tuning coil is fixed in position by adhesive tape or other means prior to permanent bonding it to a loop housing insert 35 of plastic foam such as polystyrene foam during manufacture. For purposes of clarity the foam insert 35 has been removed from FIG. 3. The input end of the transmit coil 20 is connected by an electrical lead 39 in cable 16 to an oscillator 46 in the metal detector circuit. In a similar manner, the output end of the feedback loop 24 is connected by another electrical lead 41 thru cable 16 to ground or to the other output of the oscillator when a push pull rather than single ended output is provided by such oscillator. A capacitor 40 is connected between leads 39 and 41 across the series connection of coils 20, 38, and 24. In the one embodiment with an oscillator frequency of between 5,110 Hz and 5,140 Hz, the capacitor 40 has a value of 0.33 microfarads and may be a polycarbonate capacitor with a tolerance of .+-.5%. A second capacitor at 42 may be connected in parallel with capacitor 40 to tune the oscillator output signal to 5,125 Hz. In this case, the second capacitor 42 has the selected value which is necessary to provide the oscillator frequency of 5,125 Hz. The output terminals of the receive coil 22 are connected by leads 43 and 45 thru the cable 16 to the receive signal input of a metal detector circuit 48. A third capacitor 44 of a value of 0.027 microfarads similar in type to capacitor 42, is connected between the output leads 43 and 45 across the receive coil.
As shown in FIG. 5 the oscillator 46 is of a single ended output type which has one output connected to the input lead 39 of the transmit coil 20 and has another output connected thru lead 47 to the metal detector circuit 48 to provide a reference signal. The metal detector circuit may be of any suitable type such as the metal detector shown in the patent application Ser. No. 875,677 filed Nov. 6, 1978, by James P. Karbowski. Thus the receive signal produced on the output leads 43 and 45 of the receive coil is transmitted as the input to the metal detector circuit 48 and processed to indicate whether a metal object is present in the electromagnetic field of the transmit coil 20.
As shown in FIG. 2, a grounded lead 50 is provided in the cable 16 for connection to a Faraday shield (not shown) or to the electrostatic shield 37 of FIG. 4A.
In one preferred embodiment of the present invention, the loop housing 18 was provided with a diameter of approximately 8" and contained a transmit coil of eighty five turns of No. 27 self-bonding wire. The inner diameter of the transmit coil was 6.375 inches while its thickness or height was 0.188 inches. The receive coil 22 was provided by 275 turns of No. 31 self-bonding wire and had an inner diameter of 3.188 inches and a thickness or height of 0.219 inches. The feedback coil 24 was provided by 27 turns of No. 31 self-bonding wire wrapped on the outside of the receive coil. After winding the coils were mounted in the foam core 35 and glued in place with wood glue. After nulling, the receive coil output under balanced conditions is less than 6 millivolts peak to peak amplitude and has a lead phase difference relative to the transmit signal of 40 to 100 degrees.
Now my questions. I have never made a coil myself, and do not know what connector is used for this coil, where to purchase this connector, and how to actually make this coil. If I cannot find these wires, or the wire sizes, what would I use in their place as a substitute? I would like to make a small coil, such as around 3" or 4", for gold nugget searching, and a larger coil, such as 12" or 14" or 16", for deep searching. What should I do for those sizes? Any suggestiongs? Thanks for reading and for helping, if you actually do post to help me.
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