IB Rx coil at Tx off

[Carl-NC]

You might find ordinary insulated stranded wire to be better than magnet wire. The thicker insulation reduces capacitance. You can buy stranded wire at Home Depot, probably off their by-the-foot roll.

[ZED]

Geez 24" on a quarter ,that's a stretch,you would have more luck with a mono coil me thinks,and bundle wound at that,spiral coils peter out there depth advantage when they get larger than 18" as i understand it,and they start to get very heavy.

[green]

Geez 24" on a quarter ,that's a stretch,you would have more luck with a mono coil me thinks,and bundle wound at that,spiral coils peter out there depth advantage when they get larger than 18" as i understand it,and they start to get very heavy.

A post in another forum stated a GPX4500 and GPZ7000 can detect a quarter at 24 inches. It would be difficult if not impossible based on what I've been doing. Just trying for a challenge. I need about 290ft for Tx and 380ft for Rx total to make both coils, DD and figure8. I have the magnet wire to wind them. Purchased surplus maybe 50 years ago. Magnet wire will be my first hook, if I get close maybe I might have a better idea what to try next. Different coil size, turns, wire size, maybe a mono. I'm starting with figure8 because of less noise, hoping better S/N. Trying DD because it has separate Tx and Rx same as figure8 to match my detector circuit. Wondering how much more distance the DD will get on a coke can. Also wondering what the detection distance will be for a nickel, will it still be greater than a quarter like I have now with a 8inch coil.

[ZED]

Well i have a quarter and a GPX4500 and an 18" mono but i need to go bush to see if i can get the same result,testing in suburbia gives me poor results but its winter here so its going to be a while before i get to the bush,once done
i will give you the results.

[green]

Well i have a quarter and a GPX4500 and an 18" mono but i need to go bush to see if i can get the same result,testing in suburbia gives me poor results but its winter here so its going to be a while before i get to the bush,once done
i will give you the results.

Thanks, interested in what you get when you do get a chance to try. Interested in the difference testing in the bush vs suburbia.

[6666]

Goal is to detect a US quarter at 24inches.

Awesome experiment, I hope it works for you.

[Ferric Toes]

I'm posting my attempt at detecting a quarter at 24inches for a couple reasons. Thinking the coil is important if not the most important part. Posting what I plan on doing forces me think what might be best way to succed. And hope if I'm doing something stupid someone will correct me. Not betting I can do it with 4A peak, maybe 8A peak.

For me, this thread seems to continue subjects raised in the 'Detection distance for nickel and quarter' and 'Single capacitor integrator switch'. I did some tests with my board that has the long sample pulses and I have now settled on 100uS samples as being the best for quarters without any significant loss on nickels. The space between samples has been set at 500uS. I started with the TX pulse of 350uS width and p.r.f. of about 500/sec. Start off peak amplitude of 4A and using a 8inch diameter mono coil of 310uH, I can detect a nickel at 13inches. This is using a new version of the 1C sample/hold arrangement that is perfectly balanced without an additional IC. It is an ideal match for the cross coupled inverter stage that was discussed in the other thread. Noise performance seemed greatly improved as a result.

Using my range versus coil diameter chart, a 20inch coil would increase the range to 19inches for a nickel. Going to larger coils gives diminishing returns and more noise pickup. A 36inch coil would just about give 24inches range Better to stop at 20inches diameter and put up the pulse current. Four times the pulse current would give x1.26 improvement in range, so we would be running at 16A. Things will then be running hot, including the coil, but it can be done. The 19inches range with the 20inch coil then becomes 23.9inches, which is close enough.

My 4A system draws about 0.5A at 15V, so battery capacity has to be considered when designing something for the field.

Eric.

[green]

I can detect a nickel at 13inches.reply #52


Is it 13inches for a nickel or a quarter. If a nickel what was the distance for a quarter?

[Ferric Toes]

I can detect a nickel at 13inches.reply #52


Is it 13inches for a nickel or a quarter. If a nickel what was the distance for a quarter?

Sorry, I meant quarter.

I did not measure nickels for this test except that it would be a bit less due to initial delay of 15uS and smaller size.


Eric

[6666]

Eric's chart ?

[6666]

This is using a new version of the 1C sample/hold arrangement that is perfectly balanced without an additional IC. It is an ideal match for the cross coupled inverter stage that was discussed in the other thread. Noise performance seemed greatly improved as a result.

Congratulations Eric, who would have known that after all this time a new 1C integrator could be invented.

[green]

Finished the DD Rx coil. Used DD picture in ITMD as a guide for the template. Used 24inch round for calculations. DD coil has 30.5inch max ID. Looks like should have made it a little smaller, maybe it will be all right. I'll include a picture when I finish the DD Tx.

[Qiaozhi]

Finished the DD Rx coil. Used DD picture in ITMD as a guide for the template. Used 24inch round for calculations. DD coil has 30.5inch max ID. Looks like should have made it a little smaller, maybe it will be all right. I'll include a picture when I finish the DD Tx.

This might be useful ->
https://www.geotech1.com/forums/show...767#post126767

[green]

This might be useful ->
https://www.geotech1.com/forums/show...767#post126767

Thanks, guess we will see if I projected the dimensions correctly from ITMD.

[green]

Finished the Tx coil. Next, put it together. Have a Tx circuit with 1A peak for testing. Need to make Tx circuit for 4A and greater. Still wondering how to absorb coil Tx off power. DD coil: Tx on time=300us(about 2 quarter TC's)2.2W. Tx on time=450us(about 3 quarter TC's)3.7W. Any thoughts?

Documenting coil build. Wondering what effect adding shield has. Anything else?

Rx calculates 34pf, Tx calculates 31pf. Wasn't expecting them to be as close to the same.