northwest The need for big deep gold detectors.
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australian electronic gold prospecting forum.com  |  Detector Technology and Electronics and new detectors  |  Detector Coils (Moderator: Goldman)  |  Topic: The need for big deep gold detectors. 0 Members and 2 Guests are viewing this topic. « previous next »
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Author Topic: The need for big deep gold detectors.  (Read 28579 times)
gef12
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« Reply #720 on: Sunday March 25 2018 15:10:46 AEDT PM »

No probs Ian .. take it easy mate .. my brother had both done .. just do ur re=hab ...
cheers
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« Reply #721 on: Monday March 26 2018 16:25:58 AEDT PM »

Hi all,

Jeff fine I had the Right one done 13 years ago now for the left one only this one is a bit more problematical but once done should be fine and I know all about the rehab.
 
Attached find a picture of my latest Mono spider coil I am hoping to get it finished before my opp.

Regards, Ian. happy face



* TX spider coil 002.JPG (34.76 KB, 448x336 - viewed 427 times.)
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Regards, Ian.
Muntari
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« Reply #722 on: Monday March 26 2018 16:40:22 AEDT PM »

Hi Ian,

Great work, is that masking tape you are using to hold windings?

cheers

Muntari
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IBGold
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« Reply #723 on: Monday March 26 2018 16:53:22 AEDT PM »

Hi Muntari,

The blue masking tape is a marker so when I routed the wire slots with the 1.6 mm end mill I knew where the start and finish was because the slot is being cut on the underside the litz is just pushed into the slot interference fit no need for adhesive the wires are held in place when the shield spacer is bonded on I cannot go any further until I get the foam cutter going so I can trim the shield spacers to the correct thickness.

Regards, Ian. happy face
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Muntari
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« Reply #724 on: Tuesday March 27 2018 09:33:33 AEDT AM »

Hi Ian,

Oh, Ok, I was looking at the photo thinking it was all covered in light blue masking tape, then realized, its the color of the XPS you are using,  happy face

Great job anyway, look forward to seeing how it all turns out.

I've been busy with the vacuum former and will be away with work again so might be a week or so until I can get back into it.

Hope your Op goes well too Ian, good luck with it.

Cheers

Muntari
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« Reply #725 on: Tuesday March 27 2018 15:54:03 AEDT PM »

Hi Muntari,

Yes the light blue is the IKEA XPS the green bands are the 2.5 mm XPS spacers where the wires go to the other side of the form so 10 winding's each side.

Regards, Ian. happy face
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Regards, Ian.
Aziz
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« Reply #726 on: Thursday March 29 2018 20:08:42 AEDT PM »

Hi all,

I've been busy with my sound card LCR meter. I have improved it further using a three stage complex calibration (sound card, open and close calibration using complex math). It's base accuracy is now 0.1 % (my digital LCR meter has 0.3% base accuracy). I can improve it further by measuring my reference resistors down to 0.1%/sqrt(10) = 0.032% accuracy.

Unfortunately, this is required to measure the parasitic coil capacitance. The coil capacitance caused impedance effect is low but should be measurable. I hope to be able to do it.

Cheers,
Aziz
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« Reply #727 on: Saturday March 31 2018 01:16:43 AEDT AM »

Hi all,

I've been quite tortured by the complex equations to calculate the parasitic capacitance Cp of the coil by simply making a low and high frequency impedance measurements.
 scared
It isn't that trivial. But I will make it quite trivial by Monte Carlo calculation algorithm.

I will be able to measure the Cp of the coil soon. By simply using my sound card LCR meter.
 excited
Cheers,
Aziz
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6666
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« Reply #728 on: Saturday March 31 2018 08:44:50 AEDT AM »

Keep at it Aziz, on my list of things to do, is make a simple RF oscillator, and if it works it will oscillate with just the coils inductance and capacitance, plus feed line, it will only give comparative results  between coils, but should be interesting experiment.
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6666
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« Reply #729 on: Saturday March 31 2018 14:51:54 AEDT PM »

  
Keep at it Aziz, on my list of things to do, is make a simple RF oscillator, and if it works it will oscillate with just the coils inductance and capacitance, plus feed line, it will only give comparative results  between coils, but should be interesting experiment.

Just for fun I made a VERY simple oscillator with a 40106 and the damn thing worked, I will make a better LC oscillator later, but this is what I got.
Home made bunch wind mono twisted pair feed line 1M long 243 uH 1.1564 MHZ
8" ML super gold search 296 uH  496.18 KHZ
8x6 Sadie 290 uH     501.18 KHZ
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Aziz
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« Reply #730 on: Saturday March 31 2018 18:44:08 AEDT PM »

Hi 6666,

the following Jfet LC oscillator works fine.
 smile
Aziz


* JFET-LC-Osc.1.2.png (94.82 KB, 1680x1024 - viewed 339 times.)
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« Reply #731 on: Saturday March 31 2018 22:01:21 AEDT PM »

Thanks Aziz, I will see what bits I have in the junk box.
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Aziz
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« Reply #732 on: Tuesday April 3 2018 17:29:42 AEST PM »

Hi all,

it seems, that the direct parasitic capacitance Cp measurement using an impedance meter isn't easy and requires a very very accurate measurement. The bandwidth of my impedance meter (sound card LCR meter) is limitted up to the nyquist frequency of 48 kHz (96 kHz sampling rate) and make measurements difficult. And the impedance change at high frequency (up to 48 kHz) is quite low to get accurate Cp readings.

The Monte Carlo algorithm worked very nice. But the real measurements screwed the accuracy. Overall it was a nice practice to calculate with complex numbers. I will try it again, when I have increased the accuracy of my sound card LCR meter further.

Be aware of when measuring a coil at high test frequency will give you wrong readings (higher inductance L and high coil series resistance Rs), when the coil Cp is high. But there is no problem at low test frequencies up to 1 kHz however.

Cheers,
Aziz
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« Reply #733 on: Thursday April 5 2018 20:18:31 AEST PM »

Hi all,

here is a big surprise! 

My 5 bucks sound card LCR meter is by far more accurate than the 220 bucks digital LCR meter.
What a waste of money! 

I'll upgrade my sound card LCR meter circuit to be able to calibrate into 0.03 % accuracy.

Unfortunately the measurement accuracy is required to check some coil shielding capacitance calculations and the coil software.
Cheers,
Aziz
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« Reply #734 on: Thursday April 5 2018 20:36:27 AEST PM »

  
Hi all,

here is a big surprise! 

My 5 bucks sound card LCR meter is by far more accurate than the 220 bucks digital LCR meter.
What a waste of money! 

I'll upgrade my sound card LCR meter circuit to be able to calibrate into 0.03 % accuracy.

Unfortunately the measurement accuracy is required to check some coil shielding capacitance calculations and the coil software.
Cheers,
Aziz

Why is the sound card LCR meter is by far more accurate than the 220 bucks digital LCR meter?  shocked
doug smile
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Aziz
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« Reply #735 on: Thursday April 5 2018 21:06:13 AEST PM »

  
Why is the sound card LCR meter is by far more accurate than the 220 bucks digital LCR meter?  shocked
doug smile

Hi Doug,

it is quite simple:
1. Better calibration & measurement software
2. Higher measurement resolution (24 Bit ADC)
3. Higher noise immunity (more averaging between measurements)
4. More precision reference resistors used
5. Optimal measurement range selection

I don't even need Kelvin clips & circuit to outperform an expensive digital LCR meter.

My actual accuracy is 0.1%. My next goal is to achive 0.032% accuracy.
 smile
Cheers,
Aziz
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gef12
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« Reply #736 on: Friday April 6 2018 13:19:26 AEST PM »

Hi Aziz .. must be using something as a reference for your accuracy ...  Local measurements Lab ?
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Aziz
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« Reply #737 on: Friday April 6 2018 19:51:03 AEST PM »

  
Hi Aziz .. must be using something as a reference for your accuracy ...  Local measurements Lab ?

Hi gef12,

I use high accuracy reference metal film resistors. I only have to know their exact resistor values.
I have bought a bunch of different 0.1% metal film resistors last month.
With the initial 0.1% reference resistors, I can measure lets say ten 1% resistors. When I connect the then resistors parallel, I can calculate their parallel resistor. So the value of the 0.1% resistor can be determined easily back and I can increase it's tolerance from 0.1% into 0.1%/sqrt(10) = 0.032%. Trivial task.
I have 5 reference resistor to be calibrated. Each measurement range has it's own reference resistor. Going from 10 Ohm, 100 Ohm, 1 kOhm, 10 kOhm to 100 kOhm.

Cheers,
Aziz
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« Reply #738 on: Saturday April 7 2018 13:08:40 AEST PM »

yep no probs Aziz .. sounds feasable .. I did a course " Meausurements Uncertanity" with NMI Aust years ago for our work and there was a lot of math involved.. as we calibrated "Instruments" and was required at the time .. now we out source thank god ... so dont have to go to court if there are issues now....
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Alex
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« Reply #739 on: Tuesday April 24 2018 08:53:35 AEST AM »

Hi all .I hope this is the right place to post this question.On this subject on post 431 Ian listered specs on coils.What has me confused ,is we strive for the highest resonate frequency but the 12 inch evo coil has a resonate frequency of 510khz which I thought was low  and yet has very good reviews.I hope someone in the know could explain this . Thanks again.
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australian electronic gold prospecting forum.com  |  Detector Technology and Electronics and new detectors  |  Detector Coils (Moderator: Goldman)  |  Topic: The need for big deep gold detectors. « previous next »
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