Announcement

Collapse
No announcement yet.

Minelab PI coil signals.

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Minelab PI coil signals.

    Hi All,

    There has been some discussions that ML has changed the pulse widths on their different PI models and it would be nice to know if that is true.

    Now, basic measurements of the pulse on time and pulse timing can be observed without ever getting into the detector. By using a simple coil of wire, a loading resistor across that coil and a scope, one can observe the pulse signals.

    I have attached a pic of what the SD 2100 signal looks like when observed using a simple technique of making a coil, adding a resistor across the coil leads and observing this new coil signal with a scope with the new coil a finite distance from the operating coil of a detector.

    I ran this test at the request of a well known engineer. The coil I used was a 6 1/2 in diameter with 20 turns and a 1 k loading resistor. None of these measurements are critical, so a person can use about whatever they want.
    In the case of the pic I uploaded, one can get an idea of the pulse on time of the long and short pulses as well as the general timing.

    I would appreciate anyone having one of the other ML PI models running the same test and posting the results. This way, we can see if there is any distinct difference in at least one of the operating areas.

    Thanks in advance,

    Reg
    Attached Files

  • #2
    Hi Reg,
    It looks like 3 at about 50uS and 1 at about 200uS. I am thinking the pause before the long pulse is to allow the tank cap to fully recharge. Considering the integrators will droop between pulses the trick is to get the samples close together.


    regards
    bugwhiskers

    Comment


    • #3
      If you zoom in on the decay, can you see glitches where the sampling pulse occurs? I have a 2000 and a 2200, I'll pull them out and see if I can get them working. A usable battery probably will be my biggest challenge.

      Comment


      • #4
        Someone help me out... I found 4 lead-acid batteries... (1) 6V and (3) 12V. The 6V battery has a black plastic hood over the top which includes jacks for the power cable and headphones. I assume it goes with my SD2200 because it looks brand new, and my 2200 is new.

        One of the 12V batteries has a label on top that says something to the effect of "for use only with a voltage regulator, i.e. SD2000/2100/2200". It is used, as is my SD2000. I think the other 2 12V batteries were pulled from an alarm system.

        So, I assume the following: the 6V battery is unregulated and can be used directly with either machine... the 12V battery needs a regulator to be used with either machine... the regulator is part of the battery pouch that I will need to find... is all that correct?

        - Carl

        Comment


        • #5
          Hi Carl,

          The early ML's all used 6 volts and will get very ill with 12.

          regards
          bugwhiskers

          Comment


          • #6
            Ah, I've found the battery pouch for the SD2000 and, yes, it does have a regulator in it. It's all coming together now. I've tested the batteries, all 3 of the 12V are dead, unusable. The 6V appears to be OK. What I can't find now is the charger(s). I can use my car battery charger (it has a 6V setting) but I need to make an adapter.

            - Carl

            Comment


            • #7
              Hi All,

              One of the reasons for posting this pic and request is if we can get pics of the other models using the same or very similar procedure we can tell a lot more about what is happening and some of the differences or possible differences between models.

              There has been some discussion that the later models do not go qute as deep as the older versions. If that is the case, the logical difference should show up at the signal strength out of the coil. So, we should see that difference if it exists. I, personally do not think that is the case, but I suspect we will see differences in pulse lengths.

              Reg

              Comment


              • #8
                sd2000

                Hello,

                When the sd2000 first came out I took these measurements. Using a 1K resister accross
                the Tx (no inductor). This is the timing sequence

                240uS On
                240uS off
                60uS on
                60uS off
                60uS on
                60uS off
                60uS on
                60uS off
                60uS on
                540uS off
                repeat

                Hope this helps

                regards Mark

                Comment


                • #9
                  Hi Mark,

                  They all add up to 1440 uS which means a cycle frequency of 694 Hz.

                  regards
                  bugwhiskers

                  Comment


                  • #10
                    signal

                    Hi BW,

                    Also note how the long pulse (240uS) equals the sum of the short pulses (4x 60uS). This is a clever way integrating the samples for the short and long time constant targets. As an example you take a 10uS sample in each of the short pulses, the sum is 40us. Then one 40us sample from the long pulse. These two signals are then subtracted individually from a 40uS sample at the end of the 540us off period. The result is two ground balanced signals, one for high, and one for low conductors. If you draw the logic signals it make sense.

                    regards Mark

                    Comment


                    • #11
                      Hi Mark,

                      I remember Candy referring to this as "2 detectors in 1".
                      The problem with this method of GB though is if you sweep over a target that has a TC and amplitude very similar to the ground then the target signal will be "very disappointing" I believe was the description used. In the SD2000 gold in the 1/4 - 1 oz range were the "disappointers". Recent independant testing of the 4000 in SS mode has shown that the "disappointers" are now in the 5 oz to 7 oz range, disappearing at say 12 inches and reappearing at 18 inches.

                      regards
                      bugwhiskers

                      Comment


                      • #12
                        signal

                        Hi BW,

                        Yes, in a few of patents he refers to "obscurred range of targets" which have similar TC's to the surrounding ground matrix. By taking a third sample in the mid range and combining the three linear ground balanced signals, he claims to have solved this problem. But appears in the real world, holes still exist. In the circuits and patents.

                        regards mark

                        Comment

                        Working...
                        X