Getting ready to build the MPP

[KRinAZ]

Thanks Kyle,

In the picture I posted a while back on the Chance PI Build the measurement point was at the amp input just after the back to back input diodes. Thinking back on that I'm pretty sure that the capacitance of my scope probe affected the measurement negatively. When I did the 2 stage amp design/mod on the Chance PI I was able to shave 9us from the decay signal fed to the A/D by keeping the amps out of saturation. That 2 stage mod changed the performance for the better on small gold. The MPP having a 2 stage amp should make it better for small gold than Barracuda or Surf PI. I did find that stage gains in excess of 35 did begin to add a bit of delay to the decay curve.

I would ask that you add another target to your MPP testing. A simple square piece of the side of an aluminum can cut 1/4" X 1/4" and presented flat to your coil is a pretty small target. I am interested in what detection distances you might get with the criteria being 3 consecutive passes and 3 consecutive detections for a given distance. In my testing I often get a detection at about 3" or more but on subsequent passes at that distance there may be no or sporadic detection. In order to get consistency I move in closer to the coil till I get three detections in three passes and assume that to be repeatable in the future. Anyway I appreciate you including this very small target in your future testing.

Best regards,

Dan

OK I'll do that, & oops, I made a .75" square piece, now just realized you asked for .25", I'll have that test result tomorrow...

[KRinAZ]

Thanks Kyle,In the picture I posted a while back on the Chance PI Build the measurement point was at the amp input just after the back to back input diodes. Thinking back on that I'm pretty sure that the capacitance of my scope probe affected the measurement negatively. When I did the 2 stage amp design/mod on the Chance PI I was able to shave 9us from the decay signal fed to the A/D by keeping the amps out of saturation. That 2 stage mod changed the performance for the better on small gold. The MPP having a 2 stage amp should make it better for small gold than Barracuda or Surf PI. I did find that stage gains in excess of 35 did begin to add a bit of delay to the decay curve.I would ask that you add another target to your MPP testing. A simple square piece of the side of an aluminum can cut 1/4" X 1/4" and presented flat to your coil is a pretty small target. I am interested in what detection distances you might get with the criteria being 3 consecutive passes and 3 consecutive detections for a given distance. In my testing I often get a detection at about 3" or more but on subsequent passes at that distance there may be no or sporadic detection. In order to get consistency I move in closer to the coil till I get three detections in three passes and assume that to be repeatable in the future. Anyway I appreciate you including this very small target in your future testing.Best regards,Dan

Hi Dan, ok, I cut a 1/4" x 1/4" section from the (thin) side (not from an end or close to as the can is thicker there) of a Bud Lite can, I get a good repeatable signal at 6", faint but there at 6.5". FWIW I use the "X" method to discern repeatable target signals from - ground effect, etc, - so for me a good repeatable signal that I have "X'd" is one that gives a consistent signal for usually 6 or more passes.

[baum7154]

6" is an excellent result especially for a sample laying on clean ground.

Thanks,

Dan

[green]

6" is an excellent result especially for a sample laying on clean ground.

Thanks,

Dan

I agree. I had charted the .25x.25 aluminum can awhile back. Charted more data to get a feeling what it might take to detect it at 6 inches. Not the same as KR's MPP but should give an idea of the variables. Both charts show a TC of about 1.4usec.

[Monolith]

Field at axis of current loop

I agree. I had charted the .25x.25 aluminum can awhile back. Charted more data to get a feeling what it might take to detect it at 6 inches. Not the same as KR's MPP but should give an idea of the variables. Both charts show a TC of about 1.4usec.

Practical calculator

[KRinAZ]

6" is an excellent result especially for a sample laying on clean ground.Thanks,Dan

Yes, I was surprised, you know when I was cutting that tiny target I was wondering if I would even get a target response - especially when my scale with res down to .01 grams did not show any weight measured. I guess aluminum has a very high TC somewhat like iron, without the magnetic property. Along those lines - in the past I had always used VLF machines (various Whites Goldmasters) and joked with my PI swinging buddies that their PI's just have them digging much deeper for their trash targets. Guess what - recently I had a nice signal in a creek bed that I chased, kept getting stronger as I dug & I was getting excited, at 25 inches (63.5 cm) I finally found my target - scraps of an old tin can badly rusted & deteriorated - I was amazed that I could detect it at that depth - with the 8" coil I'm using.

[baum7154]

Yeah.... aluminum can, metallized plastic juice pouches, thin rusty iron, and old tin cans are the bane of a nugget hunters searches. If only we could discriminate Al from Au on a PI machine. I was surprised to see a very thin rusty razor blade discriminate as Al/Au the first time.

Dan

[6666]

I agree. I had charted the .25x.25 aluminum can awhile back. Charted more data to get a feeling what it might take to detect it at 6 inches. Not the same as KR's MPP but should give an idea of the variables. Both charts show a TC of about 1.4usec.

Thats an interesting graph- Delay vs Signal- thanks.

[green]

Practical calculator

Thanks for the calculator. I need to enter twice the distance for the calculated field vs distance slope to match the measured target vs distance slope. Calculate 4 inches for target at 2 inches, calculate 8 inches for target at 4 inches.

[Monolith]

Thanks for the calculator. I need to enter twice the distance for the calculated field vs distance slope to match the measured target vs distance slope. Calculate 4 inches for target at 2 inches, calculate 8 inches for target at 4 inches.

That makes sense, as the calculator gives the primary field strength at the calculated distance. The secondary field, the one generated by the eddy currents in the target, then has to travel back to the RX coil.

[green]

Reply #274 I charted amplitude vs delay time for a .25x.25 in piece of aluminum can. Added more targets, California clay, US nickel, US quarter, 18 grain nugget and piece of aluminum can. Included a chart of gold nuggets I did awhile back. The TC's varied between 1.9usec and 6.6usec. The piece of aluminum can decays faster than any of the nuggets I tested. The nugget and aluminum can decay faster than clay. Adding GEB reduced the nickel, increased the quarter and did little to the nugget and aluminum signal strength. For the shorter TC targets 5.5usec or 7usec delay would be better.

[baum7154]

Good stuff Green! Looks like that 1/4 X 1/4" target is a pretty good/tough target. The gold nugget info is especially good too as it gives real world stats on what nuggets really do. I'd be interested to see how 4, 10, and 18 grain pieces of lead compare to the gold nuggets.

regards,

Dan

[Chet]

Hi Green,
Great charts as usual.
Thank you,
Chet

[green]

Good stuff Green! Looks like that 1/4 X 1/4" target is a pretty good/tough target. The gold nugget info is especially good too as it gives real world stats on what nuggets really do. I'd be interested to see how 4, 10, and 18 grain pieces of lead compare to the gold nuggets.

regards,

Dan

http://www.geotech1.com/forums/showt...get-simulation

Should be some info for different targets in gold nugget simulation. If you don't see what you want I'll try to add some more.

[Qiaozhi]

http://www.geotech1.com/forums/showt...get-simulation

Should be some info for different targets in gold nugget simulation. If you don't see what you want I'll try to add some more.

Green - I cannot remember if you've posted this already, but do you have a [simple] table of time constants for different types of target?