PI Fig. 8 Coil for Bench Testing????

[BillNEWAST]

Guys, I have spent the last 2 days searching through the posts here for a Fig. 8 coil design/specs/schematics to use on the Bench, for trouble shooting my ML SD2200V2.
I have found numerious referenches to what people have used.

BUT no design, ie.

AGW wire size =

Number of Turns =

Dia of coil =

Pin outs for the connectors and what they do??? ie TX - RX - Gnd - ect. Here is the best Reference??? but is asked as a question, not definiative.

http://www.geotech1.com/forums/showt...344#post146344

Maybe If Everyone here shares Drawings/Pictures/diagrams of their own bench coils we will have a starting point to make a Good Antifereence Bench Coil.

Sincerely
Bill Adams

[multieagle]

You may want to take this with a large degree of skepticism, but it is somewhat a miniature figure 8 coil. Whatever else, he IS entertaining.

http://www.youtube.com/watch?v=lx4I1Abm0x4
http://www.youtube.com/watch?v=P5OMuIY_oh4

[BillNEWAST]

Here's one answer from the Archives...?
http://www.geotech1.com/forums/showt...metal-detector

[Mechanic]

You may want to take this with a large degree of skepticism, but it is somewhat a miniature figure 8 coil. Whatever else, he IS entertaining.

http://www.youtube.com/watch?v=lx4I1Abm0x4
http://www.youtube.com/watch?v=P5OMuIY_oh4

LOL What a dude! Very entertaining!

Bill,

To make a simple figure 8 coil that will work well on your machine, get yourself an old 18" mono coil, pull it apart, get the winding out, cross it over into a figure 8. You will most likely have to adjust the size of the halves to get the best null out of it. Then when you are happy with it, apply some hot glue at the cross over point to keep it in its nulled position. Then you will need to apply some shielding. I used bubble wrap on mine to space the shielding from the coil. I made some shielding tape as per Stefan's instructions, 5 strands of .2mm wire evenly spaced along a length of packing tape with another layer of tape to keep the wires in place. I then just wrapped this tape around the entire coil and connected one end to coil ground. This works well.

Now, what problem are you trouble shooting in your machine?

Cheers Mick

[BillNEWAST]

Thanks Mick, I don't have the money to buy a coil and tear it apart, even though that would be the most ideal way.
I was hoping to have someone tell me to just take xxxfeet of xxx wire and coil it in a xxx dia circle and then flip it over.
I have seen where someone had used rg58 coax or something similar and made a coil from it????
Can you just use ANY OLD WIRE for a bench coil. I don't care if it is perfect or pretty, just so it Works for testing the detector.

Problem: when the sd2200v2 is turned on it goes through all its testing and such and when it does the final 3 beeps it starts
Wailing/Warbling and won't stop and it won't pick up a tin can lid at 4". I was using the Coiltek 250mm Mono and I tryed the
Stock MineLab DD that came with it, and still the same. I sent this machine to Woody last year in June and David repaired it.
When I got it back it sat till this Feb when I hooked it up to test it for this years detecting and it's making the same sound it did
last year.

I have an Audio File of the sound it's making that is trimmed to 15sec and I'll put it up somewhere and Post a Link here to it later.
I can Post High Resolution Pics of the Board and such, if you or anyone else needs to see the board/coil connectors, like I did last year
on the Noisless thread.
I tested the coils with my old Keithly and all are 0.5-7 ohm with 0.285mH my inductance meter won't measure to microH.
I took the machine 10 miles south of the Big Power Substations at the Dam and 1.5mile from the residential lines.
Still won't settle down and Won't pick up a 34mm brass medalion either.


ps I live within 1.5 miles/2.4k of The Dalles Dam on the Columbia River, and 1000ft of the small regional AirPort in Dallesport, Wa USA

Thanks again and will be figuring out how to post the .mp3 file for everyone to hear.
Sincerely
Bill Adams

[Carl-NC]

Just wind up a coil, twist it into an '8', and see what you get. For bench testing just about any wire will do, and shielding is optional. Try 24awg stranded PVC, 12" diameter, 24 turns. After you twist it, measure the inductance and adjust the turns if the L is much over 300uH.

[BillNEWAST]

Thanks Carl will do that.
do you know how or where to upload a 15sec mp3 file of the noise the detector is making???

[Carl-NC]

Try "Manage Attachments," I just added mp3 as a valid file type. Have no idea if it will actually work.

[BillNEWAST]

Ok Carl here goes the TEST it is in a mp3 file.
When I tried to load it it said it was 815kb which exceeded the 100kb for this file type.
Carl can you reset the SIZE for that or do I need to Shrink it more.
I'm afraid that the 15 sec file @ 800kb won't be enough to listen to @ 15sec/factor of 8 = 1.87sec!

While I wait for your answer I'll check on what the file size is for a WAV file.
I checked and the wav file type for the same file is 4Mb+-.

The smallest I could get the file and have it make sense is 775kb @ 12.99sec. and this is for the MP3 file type.
I'll use my audio software to see if I can save the file in another format and get closer to the 100kb restriction.
If you can change the 100kb restriction to 1000kb then I'm sure that anybody could load a 15-20 sec file of what their
machine sounds like and this would help others on the forum be able to identify what a sound is associated with a problem.
Sorry to be such a PEST!

Sincerely
Bill Adams

[Mechanic]

HI Bill,

Ok, for a start, have you tried it with the mod switches in the centre position?
Now get your scope, hook the ground lead to the test point between the 2 thick coil wires, this is detector ground.
Hook your probe up to the ( with the board edge that the coil wires are coming from toward you and the coil wires on the left hand side) test point to the right near the trim pots, but the one closer to the centre of the board. set your scope to 100mv/div(probe x1) and about 100us.div. You will be able to see the decay curve, grab a large metal something and move it onto the coil, the decay curve should move a lot. If not you have a problem in the front end and we need to scope it further.

Just do this with a normal coil.

Cheers Mick

[Carl-NC]

OK, I increased it to 1M. I routinely make music MP3s at ~500k/minute (still very high quality) so try to keep the size down.

[BillNEWAST]

Carl, how do you do that???
What software do you use and what are the settings to get ~500k/min.

I am using Sony's Sound Forge Audio Studio.
I also have Audicity and sonys voice software that came with the Digital recorder.

Thank you.
Sincerely
Bill Adams

Here is the Audio of the Detector!

ML 130318_001.mp3

[Mechanic]

HI Bill,

Does bumping the case have any effect more/less noise or create a response?

It does not sound like a happy detector!

Please do the tests I suggested above and attach some scope shots with and without a target if you can.

Cheers Mick

[BillNEWAST]

Carl, I made a fig 8 coil with 24awg apx 12" dia and I got 305uH and 1.8ohms. Will 1.8 ohms be too much for the machine??
or should I get some 18 awg and wind a 18in dia. x.25 ln 19 turns coil from 90ft of wire?? it would equal out to 0.57ohms x 316uH
acording to Gary's calculator here. http://chemelec.com/Calculators/A-Inductance2.htm and
on this site http://www.circuits.dk/calculator_mu...er_aircore.htm


Mick, I don't think that bumping the case has anything to do with the sound. I have it apart now and am setting up the Scope to use.
here is a pic of the Coil side of the end cap and upper left of the board. My other pics I posted last year on the Noiseless Thread are still there also.
Pins 4,5 are White Pin 3 isn't connected and Pin 2 is Blue and Pin 1 is Yellow. Anyone got any Ideas on what the Pins are????
Any Guesses on what the IC is in the upper Right is??? NO markings and apears to be only 2 Pins.

[Carl-NC]

Most likely, for bench testing, the high R isn't going to affect much. If you're concerned about it then 18awg would be a good size, wire R drops in half every 3 gauges.