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  • #91
    coil shielding PI

    Thanks again for the clarification. Just laid down the first coat of graphite/polyvilylacrylic finish in a 50/50 volumetric mix. It will be dry enough to check in 2 hours but won't have anything definitive till tomorrow. Extra coats will likely be needed and certainly using your method of progressive ohmic checks throughout the coil will take some more time and adjustment. I will shoot for 1500 ohms/inch and see what happens in the field before putting on the final fiberglass layer.

    Regards,

    Dan

    Comment


    • #92
      Originally posted by baum7154 View Post
      Thanks again for the clarification. Just laid down the first coat of graphite/polyvilylacrylic finish in a 50/50 volumetric mix. It will be dry enough to check in 2 hours but won't have anything definitive till tomorrow. Extra coats will likely be needed and certainly using your method of progressive ohmic checks throughout the coil will take some more time and adjustment. I will shoot for 1500 ohms/inch and see what happens in the field before putting on the final fiberglass layer.

      Regards,

      Dan
      Hi Dan
      You need at least 24hrs before checking/doing changes , you will find within the first few hours of applying the graphite readings will be up and down like a yo yo, by many ohms.

      Regards

      Comment


      • #93
        Shielding

        Sound advice! I checked resistance this AM and it was markedly different than last night...due to shrinkage/curing? I'll keep an eye on it till tomorrow before I add another coat. first coat is running about 8K ohms now.

        Thanks

        Comment


        • #94
          Shielding Chance PI

          After 3 coats of shielding material as mentioned previously and lightly sanding the coil, the resistance overall is between 1200 and 1500 ohms top and bottom. It was interesting that the ohmage went down at first when sanding and then began to raise with more sanding. This was due I think to better contact with the test leads at first and then removal of conducting material as the coating wore thin. Now on to testing for fine gold sensitivity!

          Comment


          • #95
            Your getting the feel how the graphite works Baum, thats where alot will fall on there bums not reading the signs, its funny stuff but once settled its very stable.
            Ive now finshed the Minipulse3 , up and running, hey what a powerful bit of kit, took it to my test bed in the real world about 2 hours ago, very impressive considering the coil that I quickly made up, shall shield tomorow and we can compare results later in the week.
            Thanks for going the extra mile Baum your a gent.

            Regards
            Attached Files

            Comment


            • #96
              Shielding Chance PI

              Thanks for the help on this. The process is time consuming and I had decisions to make on the 'varnish' and the graphite that only experimentation would prove out. The results of air testing are quite gratifying with the graphite shielding! I mentioned before that the unshielded high speed spider coil would operate down to a 19 'Guard Interval' setting on my Chance PI. After initially shielding it with copper foil the Guard Interval had to be set to 34 before the unit would operate, but it did detect most metals pretty well. The 34 setting was evidence of a significant slowdown of the spider coil due to increased capacitance with the windings. As a result it did not detect small fine gold well or at all.

              After removing the copper foil and installing the graphite shield as you outlined, the Guard Interval can now be operated at 19 again though that is on the hairy edge of stability. I prefer to operate it now at a setting of 20. Fine gold can be detected at a distance of about 9 cm. I need to spend time in the field with this detector once it is fully integrated into a package to get real world in-ground tests here in the Colorado Rocky Mountains. I have seen comments on these forums that indicate the in-ground tests can be even better than the air tests. I hope this is the case.

              There many settings to optimize on the Chance PI for the detection of small placer gold and this can only be properly done in the field. I have seen some instances of slight detection of my match head volume of gold flakes in air at a distance of 25cm or so. This is with an 8" spider coil . It is not consistent enough to rely on though. Thanks again for the assistance and the information...YOU are a Gent sir!

              Regards,

              Dan

              Comment


              • #97
                Originally posted by baum7154 View Post
                Thanks for the help on this. The process is time consuming and I had decisions to make on the 'varnish' and the graphite that only experimentation would prove out. The results of air testing are quite gratifying with the graphite shielding! I mentioned before that the unshielded high speed spider coil would operate down to a 19 'Guard Interval' setting on my Chance PI. After initially shielding it with copper foil the Guard Interval had to be set to 34 before the unit would operate, but it did detect most metals pretty well. The 34 setting was evidence of a significant slowdown of the spider coil due to increased capacitance with the windings. As a result it did not detect small fine gold well or at all.

                After removing the copper foil and installing the graphite shield as you outlined, the Guard Interval can now be operated at 19 again though that is on the hairy edge of stability. I prefer to operate it now at a setting of 20. Fine gold can be detected at a distance of about 9 cm. I need to spend time in the field with this detector once it is fully integrated into a package to get real world in-ground tests here in the Colorado Rocky Mountains. I have seen comments on these forums that indicate the in-ground tests can be even better than the air tests. I hope this is the case.

                There many settings to optimize on the Chance PI for the detection of small placer gold and this can only be properly done in the field. I have seen some instances of slight detection of my match head volume of gold flakes in air at a distance of 25cm or so. This is with an 8" spider coil . It is not consistent enough to rely on though. Thanks again for the assistance and the information...YOU are a Gent sir!

                Regards,

                Dan
                Hi Dan
                It is messy and time consuming only because of the wait for drying period,dont to date know of away round that because adding other components to make it dry quicker which i tryed yeild it brittle and flaky.
                I got the itch now, is the Chance worth the build in your opinion, the tests so far are outstanding with the Minipulse3 just as the spec sheet says and intend to do a construction thread on it, but of course its got know discrimination, im led to beleve that there is with the Chance, is this correct? or is it folly

                Regards

                Comment


                • #98
                  IS CHANCE WORTH BUILDING

                  Satdaveuk your question is difficult for me to answer as I have not yet had this unit in the field.

                  Comments I have read on line indicate that the discrimination is only mediocre and that greater detection depth is needed. Regarding these comments I can tell you that the discrimination of Iron is solidly indicated on the right side of the readout. My 10K gold ring reads 8-10 on the 16 point wide scale as it should because it is not pure gold. The placer flakes I use in testing indicate on the left side of the scale as they should. Copper indicates on the left end of the scale as well. Aluminum indicates a few divisions from the right end of the scale. If you need to differentiate metal based on the scale indications I'd say that only the differences between iron and gold/copper are reliable.

                  Regarding the depth issue I really have no experience yet. I only know that everyone wants more depth on small targets and we all know that large coils look deeper on medium to large targets. I'll have to report the field results on old gold dredging piles once this unit is complete. Better yet would be controlled tests in clean ground where I can bury a variety of metals in a variety of sizes in a variety of orientations at known depths.

                  In the tests I've done in my yard the unit easily sees iron and lead targets but the problem is that my yard is scattered with targets and I really don't want to dig up the lawn. Maybe I'll go into the garden and try to clear an area for testing. So much to do. It is fun!

                  Comment


                  • #99
                    Same boat as me got the test bed and outer of that is lawn, lots and lots of hits some worth the dig but dont want to bugger it up as spent a fortune making it nice over the years even though still lots of weeds.
                    Keep us informed of your updates its interesting.

                    Regards

                    Comment


                    • Cheap solid copper Teflon wire

                      I have not seen this source for untinned solid copper Teflon wire listed anywhere on this forum. After seeing all kinds of silver plated stranded teflon wire on EBAY I recently stumbled upon CAT5 and CAT6 PLENUM RATED cable. This cable is typically composed of several twisted pairs of 23 or 24 awg plain copper wire and is usually Teflon insulated. The Superior Essex brand of 77-240-2B cable lists it's wire insulation as FEP, a Dupont designator for one of it's teflon products.

                      The downside of using this wire is that you have to strip the outer sheath and untwist the inner pairs from each other. The the cable does come with a nylon sheath stripper thread with the wires so stripping the sheath is not difficult. The inner core can be unwound with a cordless drill by clamping one end of the wire bundle to a table or vise and the other end pinched in the drill chuck. Gently pull the bundle taut and set the chuck to unwind the bundle and you will eventually have 4 sets of twisted pairs colored Blue, Orange, Green, and Brown.

                      Once again you can unwind each of these twisted pairs using the cordless drill. In the end you will have 8 each 23awg teflon insulated solid copper wires. If you want to straighten the slight twisting ripple from the wires you can weave and pull them through a set of 4 to 6 nails clamped in a vise jaw and set about a 1/2 inch apart. They are woven through the nails much the same as a skier goes through slalom gates.

                      A 75' piece of this cable will yield about 600' of this wire.

                      Have fun!

                      Dan

                      Comment


                      • Chance build

                        I have been building/optimizing the Chance for about two years. Started with software version 0.8.4 and currently running 1.2.1. The software much improved the performance.

                        Recommend the axial lead 220uh choke be avoided and replaced with one capable of greater current handling capacity. I wound my chokes on toroids using 26 awg enameled copper wire.

                        Also the author's original basket weave coil is OK for coins and jewelry but not for fine/small gold flakes. I am using a 'spider wound' 8" coil for small gold detection shielded with graphite al la Satdaveuk process outlined in the COILS forum with a heading of Graphite Shielding.

                        All schematics of the Chance detector are in detached form but the website is pretty clear. If you have Silverdog's recent boards you can ignore the Mods required for the older production boards. I have done one of each.

                        I use the OP37 opamp as it has superior parameters to the NE5534.

                        Regards,

                        Dan

                        Comment


                        • Graphite Shielding

                          Correction to my previous post. The info is in the COILS forum under SYNTHETIC GRAPHITE. Sorry for the error.

                          Comment


                          • Hello Dan!
                            Gratulation to your Chance.
                            How many uH have your selfmade choke now?
                            How accurate is your metal indicator. Is it now possible to know what is iron?

                            Greetings from germany

                            Comment


                            • Spidercoil

                              I did not take a picture of my spider coil but it is built on a 4.5 mm Lexan form that I machined with 37 slots on the outer rim and 37 on the inner rim staggered to the midpoint between the outer slots. This is quite similar to the form pictured back in this thread. I wound this coil with 26 awg enameled wire and I believe it was 37 turns of wire. The form is 2.5cm in width and the slots are cut 6mm deep. I used an LCR meter to get the coil to a value of 412uh including the shield and coax.

                              Regards,
                              Dan

                              Comment


                              • Toroid choke

                                The choke is 280uh. Iron always indicates on the right end of the scale. Gold placer always on the left of the scale. Alloys of gold i.e. 10K gold appears about mid scale.

                                Comment

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