MPP coil test

[geoscash1]

Hey guys,

Any one have a good educated explanation as to whether this looks good or not? (short video below)

Been messing with different damping resistors, series resistors and coil winds and finally got what I think is a pretty quick coil with the board set up and adjusted very good.

I did a real quick vid of scope while checking the voltage change on the coil pulse flyback with the sample pulse over laid.

Scope settings are coil pulse (TP4) 1v/div-10us time delay - sample pulse (TP7) 2v/div-10us time delay. Coil is 7-1/2" 3dss with 175/46 litz, 31 turns, 2.1R double layer wire wrap. Sample delay set to minimum 6us.

Getting good detection with air tests but wanted to get some experienced view points as to what the scope is telling me, could it be better? does it look as good as I think?

It looks to be pretty good, fast coil pulse flyback recovery @ under 10us with good quick target recovery.

[geoscash1]

With some fine tuning on the delay (about 7us) and sat (full) with sensitivity at around 90% and threshold at slow tick I'm getting these results now.

US nickel - 14"
14k ring - 11"
1.2 gram nugget - 6"
8 grain nugget - 3"

With my 6x10 razorback factory coil (312uH/2R shielded/folded mono) the results are as below,

US nickel - 11"
14k ring - 10"
1.2 gram nugget - 5"
8 grain nugget - 2"

She is working pretty well so I have everything documented with values and adjustments. I still need to build a larger coil
to test with and see how much it changes or improves. Will make a 9" or 10" round using the same litz and one with 24awg Teflon 7 strand.

[Rayjay]

geoscash1,

Let me know how you make out with your 9" or 10" round coils using litz and 24awg Teflon 7 strand wires.

Thanks

[green]

Hey guys,

Any one have a good educated explanation as to whether this looks good or not? (short video below)

Been messing with different damping resistors, series resistors and coil winds and finally got what I think is a pretty quick coil with the board set up and adjusted very good.

I did a real quick vid of scope while checking the voltage change on the coil pulse flyback with the sample pulse over laid.

Scope settings are coil pulse (TP4) 1v/div-10us time delay - sample pulse (TP7) 2v/div-10us time delay. Coil is 7-1/2" 3dss with 175/46 litz, 31 turns, 2.1R double layer wire wrap. Sample delay set to minimum 6us.

Getting good detection with air tests but wanted to get some experienced view points as to what the scope is telling me, could it be better? does it look as good as I think?

It looks to be pretty good, fast coil pulse flyback recovery @ under 10us with good quick target recovery.

Scope traces look good to me. Wondering if increasing the delay about 1/2usec wouldn't be better. Start sample after amplifier out signal returns to zero.

Looking at traces again, how long is the sample pulse?

[homefire]

What's the deal at 17 sec or so with the Signal dropping out like that with the audio tics ? Is it power hungry ?

[green]

Scope traces look good to me. Wondering if increasing the delay about 1/2usec wouldn't be better. Start sample after amplifier out signal returns to zero.

Looking at traces again, how long is the sample pulse?

Don't have a MPP. Qiaozhi posted a simulation awhile back with 58usec for the sample length. The scope trace looks like a lot less. What am I missing?

[geoscash1]

I believe my samples are set to 15us.
Id have to dig the boards out or find my notes. But pretty sure they were set to a final of 15us after testing at 12us.

[green]

I believe my samples are set to 15us.
Id have to dig the boards out or find my notes. But pretty sure they were set to a final of 15us after testing at 12us.

Thanks for the reply. Changing the sample time effects the integrator response time. Somewhere I think I saw a schematic with a pot across U8B pins 6 to 7 to adjust response time. Does your MPP have one or isn't it needed?

[eclipse]

You can change the TC of the integrator by changing 56K resistor value, 56K-300K.
The trimmer you probably have seen in the Superscan schematic which is almost identical.

[geoscash1]

Thanks for the reply. Changing the sample time effects the integrator response time. Somewhere I think I saw a schematic with a pot across U8B pins 6 to 7 to adjust response time. Does your MPP have one or isn't it needed?

Not sure of U8B, I only see U8. But, as far as trimmers go, I did mod R7/R8 with trimmers and also R10/R11 so I can adjust the main tx pulse along with freq and sample pulse widths as well as delays. Also added the sensitivity pot with a series resistor as well as changed resistors on the volume/PL6. All of the mods from Kyles (KRinAZ) thread.

The final settings on the board being tested here I used 34us on the main tx pulse, sample delay is adjustable from min 6us to 28us max (or there about's on the max), sample widths are set to 15us with the frequency set to 3250 pps.

Depending on which coil I plug in (after hours and hours of testing, adjusting and readjusting) using my 3dss 250/46 litz or my razorback 5x9 shielded coil, the final results were exactly what I wanted with either coil. It detects my .45 gram (8 grain) nugget at 3.75 inches, a 1.2 gram nugget at 6", a 14k ladies gold ring at just over 11".

I had to take my gear away from my house up to the hills to get these readings, to much interference and chatter around my home and in my garage. Once I was in the woods, this thing detects and works exactly as I had hoped.

Its best delay setting is around 7-1/2 to 8us, it doesn't like anything under 7us at all, to much chatter. I am super pleased with the results of all 3 MPP boards I have built, 2 are in working units ready to roll when the weather breaks and the other is almost cased and ready to be mounted.

Hope that helps answer your question, my health hasn't been so good lately and I haven't been able to do much more than walk down my driveway and back (about 60ft total) without feeling like I just ran a marathon, chemo is taking its toll and tomorrow is another round for 3 days.

I'll try to answer any questions as best I can.

Geo

[green]

Hi geoscash

Thanks for the reply, wish you the very best with your health.

[geoscash1]

Hi geoscash

Thanks for the reply, wish you the very best with your health.

Your welcome... and yep, workin getting better..

here is my settings on a graph from the build doc.

[Roo2]

Hi there,
I've returned to finish off my MPP project after a long break.. Last year I wound a couple of 10" coils using the "criss-cross 3DSS" concept.. One with Litz wire and one using PTFE coated wire. It's been a while.. I recall both had more windings than I calculated as necessary at the time. I recall someone had written a nice "tuning procedure" where the coil is progressively unwrapped one turn at a time until the detection distance stops improving. Could someone point me to that nice little write up? I can't find it.. Mostly interested in how to manage the unwrapped wire tail without cutting too much off before being confident I've found the right number of turns.
Thanks, Andrew.

[baum7154]

I believe you are referencing a write up I did in the Chance PI Coil thread some years ago. This was in the Coils section of the Forum.

[Roo2]

Thanks Dan. I think I’ve found it:

• 
  Without test equipment I recommend that you cut the slots a little deeper to allow 40 turns to fit in the coil form. Then run the following tests;
  1. Make some small test targets of varies sizes from an aluminum can and some small lead targets. Don’t worry about coins at this time, they are easier to detect than small aluminum and lead.
  2. Test the targets with your existing coil setting on the ground or on a plastic waste basket. Make sure there is no metal nearby. Wave each target over the coil and record the detection heights.
  3. Now place the new 40 turn coil in the same position with the coil cord or twisted pair that connects the coil to the detector. Connected in a manner that you can easily disconnect the outer wire to unwind it one turn at a time. This may require cutting and soldering each time. The final solder joint will not affect the coilperformance.
  4. Wave each test target over the new coil and compare the height to the previous height recorded. It may not detect the smallest test targets until some turns are unwound.
  5. Unwind one turn laying the extra wire length out into a wide loop away from the coil and solder it to the end of the coil cord to repeat the test again.
  6. Repeat measuring and unwinding coil turns until you pass through the best height measurements.
  7. Add a turn or turns back if you pass up the best measurements.
  8. Cut and remove the long arc of extra wire.
  9. Solder and insulate the final connection.
  10. Save the targets and the final test measurements for use with future coil builds.
  
  
  
  
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