Announcement

Collapse
No announcement yet.

TGSL Tuning & troubleshooting

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

  • values coils tgsl

    hello , values coil tgsl are 5,9 and 7 mH , What value should I put c6 for it accords with my Rx 7 mH?
    __________________
    hello , Nico
    Nico:

    Use formula for resonant freq and choose C6 so resonant freq of RX is 1.11 times the Tx oscillator frequency.

    You will find formula somewhere in this thread or other TGSL threads. http://www.geotech1.com/forums/showp...&postcount=494

    And please learn how to post to this forum. Maybe Qiaozhi can send you another email (I hope).

    Regards,

    -SB

    Comment


    • I already had them writ, so may as well post. (Drawn with Design Science MathType.)

      Attached Files

      Comment


      • TGSL Oscillator/Discrimination question.

        Today I changed R3 in the oscillator circuit which is the 47k from base to ground with a 100K PCB pot. This is the change that was noted by Ivconic when he wrote up the IGSL thread about a year ago.

        The purpose was to fine tune the oscillator for a nice sine wave and get rid of the little bump at the top of the TX waveform that we are all used to seeing in oscilloscope pictures.

        This cleaned up the TX waveform really nice. However it also changed where things discriminate. For example, nickels used to null out at mid rotation of the Disc pot or about the 12 o'clock position. After the changes, it moved clockwise to between the two and three o'clock position. Pull tabs are silenced further clockwise but Zinc pennies are not. Note...... I could not silence zinc's prior to the tx change so that is nothing new.

        It was raining today so I did not take it outside to the test garden but the air tests are as good if not better than before the change. It is supposed to rain again tomorrow so it looks like this will be the project for the day.

        I am confused as to why a cleaner TX signal would change the discrimination. Anyone have any ideas?

        Jerry

        Comment


        • Hi to all

          I maked TGSL with this information in attachment
          And its very cool and it discriminator is nice too !

          But that sense is low in my mind
          It detect a 1 penny in about 20 cm in air and a gold coin (2.03 g) in 15 cm .is this correct ?
          tx=6 mH and rx=6.5 mH

          thanks

          freedan3d
          Attached Files

          Comment


          • Originally posted by Jerry View Post
            I am confused as to why a cleaner TX signal would change the discrimination. Anyone have any ideas?

            Jerry
            Try measuring the TX frequency before and after the change. I suspect you will find a difference. If so, you can compensate for this by adjusting the value of the tuning capacitor.

            Comment


            • Originally posted by Jerry View Post
              Today I changed R3 in the oscillator circuit which is the 47k from base to ground with a 100K PCB pot. This is the change that was noted by Ivconic when he wrote up the IGSL thread about a year ago.

              The purpose was to fine tune the oscillator for a nice sine wave and get rid of the little bump at the top of the TX waveform that we are all used to seeing in oscilloscope pictures.

              This cleaned up the TX waveform really nice. However it also changed where things discriminate. For example, nickels used to null out at mid rotation of the Disc pot or about the 12 o'clock position. After the changes, it moved clockwise to between the two and three o'clock position. Pull tabs are silenced further clockwise but Zinc pennies are not. Note...... I could not silence zinc's prior to the tx change so that is nothing new.

              It was raining today so I did not take it outside to the test garden but the air tests are as good if not better than before the change. It is supposed to rain again tomorrow so it looks like this will be the project for the day.

              I am confused as to why a cleaner TX signal would change the discrimination. Anyone have any ideas?

              Jerry
              I think Qiaozhi's idea sounds very plausible -- let us know what you find.

              One problem with getting rid of the bump is that the oscillator amplitude may be less "stable" (more affected by ground and other effects) - and you may lose a little depth. But it should help clean up some sync pulse generation messes if you have them.

              -SB

              Comment


              • Hi Jerry, Adjusting the R value has biassed the device on less - so its more linear.
                Spectral output is cleaner.

                The amplitude may have decreased a little too.


                If the amplitude is a little lower the trigger point at the detector is later in time (phase) - so you see the shift in desc setting.

                Steve

                Comment


                • I just spent a couple hours checking to see if a shift in TX frequency or voltage is causing the problem and it is not. I was surprised to see that the TX frequency was 14.21 Khz. Fortunately all of the transistors and IC's on the TGSL are socketed so it was a simple matter of removing the TX transistor and connecting a sine wave signal generator.

                  With the signal generator, I checked ground balance and discrimination settings while moving the frequency from 14.2 to 14.8 Khz and changing the TX voltage from 8 to 18 volts.

                  After each change in frequency or TX voltage, I did reset the ground balance. Sometimes by a lot. However, the point at which nickels would discriminate out changed very little and seemed to be in the 2 o'clock position of the Disc knob.

                  I am satisfied that frequency and/or voltage shifts are not the cause of the problem in this particular machine. I agree that they probably should so there is a problem somewhere on my board. I even put my old 8 inch coil with the heavy foil shielding and tried it. It discriminates the same way. At least things are consistent.

                  Once again, the machine is very usable the way it is and gets good depth on coins. My issue is with the ability to ID coins or trash with the Disc control. I should be able to discriminate out all targets up to and including zinc pennies.

                  I did take a series of pictures of the signals from U-101, pin 7 and the Gate of TR-4.

                  No. 1 shows the Disc at minimum. (counter clockwise)
                  No. 2 is with Disc at ten o'clock where the dip in the square wave just goes away. It seem to hit a very critical point where a very small movement of the disc control makes it blip out completely. It does however leave a small dimple in it's place at the top.
                  No. 3 is Disc at 12 o'clock, mid rotation.
                  No. 4 is at 1:30 where the trailing edge just stops moving to the right as the disc is advance clockwise. The rising edge does keep moving as the disc is turned further.
                  No. 5 is with the disc full clockwise. Width of the top of square wave is no as wide as it was and the bottom is wider.

                  Also of interest is the slight bump on the U101/7 signal that moves with the square wave and then coincides with the spike on the trailing edge at maximum rotation.

                  I checked the value of R18, the 100K Disc pot and it measured 74K from end to end so I replaced it with on that measures 97K (closest I had) and it did not change anything.
                  I am using MPF102 JFET's for TR4 and TR5. Don't know if that is an issue or not but looking at this part of various Tesoro circuits I don't see where it would be.

                  So that is my progress, (or lack of) so far.

                  Looking for ideas.

                  Jerry
                  Attached Files

                  Comment


                  • Simon,

                    I remember you posted a voltage divider mod for the signal from the TX to the Disc and GEB circuits a while ago. Other than cleaning up the Disc pulse when set at minimum, did it have any other benefits for discrimination? As long as I have the covers off, I just may do that and see.

                    Jerry

                    Comment


                    • I just noticed something about the series of pictures that I posted. By coincidence, the center vertical graticule is very near the dimple at the top of the square wave. It starts out where the rising edge of the right hand double bump is and the square wave seems to pass in front of this point and it finally falls off to the left or rising edge in the 5th picture.

                      It is amazing the details you can see once you put a picture on a big computer screen

                      Do not understand the significance of this but it is just an observation.

                      Jerry

                      Comment


                      • Originally posted by golfnut View Post
                        Hi Jerry, Adjusting the R value has biassed the device on less - so its more linear.
                        Spectral output is cleaner.

                        The amplitude may have decreased a little too.


                        If the amplitude is a little lower the trigger point at the detector is later in time (phase) - so you see the shift in desc setting.

                        Steve
                        Hi Steve,

                        I missed your post until I read my email. You are right, the amplitude increases until the oscillator is saturated and they starts clipping the top peaks. I backed it down just enough to clean it up.

                        For some reason, setting it back to where the bump at the top reappears does not fix the discrimination problem. I caused a change somewhere but have not found it yet.

                        Jerry

                        Comment


                        • Originally posted by Jerry View Post
                          Simon,

                          I remember you posted a voltage divider mod for the signal from the TX to the Disc and GEB circuits a while ago. Other than cleaning up the Disc pulse when set at minimum, did it have any other benefits for discrimination? As long as I have the covers off, I just may do that and see.

                          Jerry
                          Hi Jerry:

                          I did not see any other benefits that I could measure. I actually expected to possibly get some depth improvement because it eliminates the "double pulse" (as seen in your top scope photo) that can happen, which diminishes the integration interval of the Synchronous Detector JFet. However, I believe that the ground-balance channel always has a weaker signal than the DISC channel, and so is the limiting factor, and as a result degradation of the DISC channel is not noticed.

                          In my circuit however there is a capacitor (I called it Cdiv) that compensates for a slight phase shift that the circuit introduces -- this gives you some control over the "phase bias" of the DISC control, if you want to play with values of the cap.

                          Another way to change the phase bias is with a small capacitor (like 10pf to 50pf) in parallel with the feedback resistor R17 of U101b (LF353). Someone else talks about it, I forget who. I don't know if such a cap would shift the DISC phase bias in the right direction for you, but it is worth a try, and easier to install than my mod.

                          I would like to see your scope picture of the output of U101b (pin 1) that drives the U102a LM393 DISC pulse shaper -- it would be good to see this output for both cases, where you adjust the oscillator for no bump, and with maximum bump. Or am I mixed up -- are you using pin 7 to drive the LM393???

                          I wonder what changed in your circuit? I agree with golfnut that the trigger point of the pulse generator (and thus phase bias) can be sensitive to the "oscillator bump", because that bump becomes a real blip at U101b pin1, and typically that blip is near the zero voltage trigger point. However, the puzzle is why when you restore the bump you don't go back to your previous operating point?

                          Here is a link to the "voltage divider" mod I did for reference: http://www.geotech1.com/forums/showp...9&postcount=73

                          -SB

                          Comment


                          • Thanks Simon, that is the one I was thinking of. Will try and get a picture of U101b-1 and post it later today. Right now I have a huge lawn that needs cutting

                            Jerry

                            Comment


                            • Originally posted by ivconic View Post
                              Exactly.
                              Proper coil nulling is not an easy job. I think most people understood nulling as just simple task. Pitty, it is not like that.
                              At some coils i spend 5-6 hours to null them properly. Amateur conditions do not offering me comfort, so nulling is time&nerves consuming tough task.
                              Than again...at some coils i achieve good balance in just 20 minutes.
                              It is all about quality made and details.
                              Usually i am using hot melted plastic glue gun and put "punkts" (points) over the coil to attach it to holder good. Than i must wait hot glue to dry and get cold. Than again to correct balance by slitest (parts on millimeter) movements of some coil segments. Than again to wait to see influence of temperature changes in workshop....and again..and again. All the time RX coil is attached to millivoltmeter and observed. TX coil is attached to TGSL TX out.
                              Sometimes process is going pretty smooth and everything ends in 20 minutes....but sometimes it took time to be done. It can took hours sometimes.
                              Once coils are balanced well i use joint filler (2 components epoxy) to finish coils. It all must be done in one move, fast, not to allow temperature changes to affect balance. If you balance coils and let them overnight....those will move for sure and spoil the balance much.
                              Tough job to make good coil in amateur conditions. Not easy.


                              ....

                              That's why i am thinking to give up of making DIY coils finally, lately. It is more cheaper to buy original coil and adapt detector to work good with it.
                              Hi ivconic

                              I see your tgsl test video and i am so excited
                              its very cool ,man !!!
                              and i decided to make that. i finish it now .
                              but it is not seem to your tgsl depth !
                              it detect a 1 penny in 20 cm in air and a gold coin (90% gold ,2.03 g) in 15 cm
                              is it a good depth ?
                              my coil tx=6 mH and rx=6.5 mH
                              what is the best coil rx,tx inductance ?

                              many tanks

                              freedan3d
                              Attached Files

                              Comment


                              • TGSL U101b-1 Pictures.

                                Hi Simon,

                                Here are a few pictures showing what happens while adjusting the TX oscillator. The changes with just a little distortion in the TX sine wave is interesting. The bump produces noticeable ringing. The upper trace is the TX signal measured at J1 and is set at 5 V/div. The lower trace is U101b, pin 1 and is set at .2 V/div. Same setting apply to all pictures.

                                First picture is the TX oscillator (top signal) tuned for a clean sine wave.

                                Second shows the TX oscillator with about as much bump at the top as was there before I added the adjustment pot.

                                Third is somewhat in between with just the slightest of bump at the top. Even with that, there is still ringing.

                                Interesting at how the Disc pulse amplitude goes up with more distortion of the TX sine wave. I suppose the next question is how much is needed for good discrimination. I am too wiped out right work on it tonight but it gives me quite a few ideas.

                                Thanks for suggesting this, it is interesting.

                                Jerry

                                Now that I think about it, I did not even look at the Disc knob settings..... whatever it was, it is the same for all pictures. Will check some more tomorrow.
                                Attached Files

                                Comment

                                Working...
                                X