Can pinpointer detecting thin chain?

[Qiaozhi]

Thanks Qiaozhi. Great! I will try it now.

Total Inductance =

Mutual Inductance M:



Can I preview this message to see if it works without having it put up in the forum straight away?

Yes - click on the Go Advanced button. There is a Preview Post button there.

[Polymer]

Thanks Qiaozhi. Great! I will try it now.

Total Inductance =

Mutual Inductance M:



Can I preview this message to see if it works without having it put up in the forum straight away?

[Qiaozhi]

M = k times square root of (L1timesL2) How the hell do I get math notations in here?

You need to use LaTeX. It's embedded in the forum.

For example:
Enter: [latex]M = k * \sqrt{L_1*L_2}[/latex]

to display:

Syntax guides can be found here:

https://en.wikibooks.org/wiki/LaTeX/Mathematics

and here:

https://wch.github.io/latexsheet/latexsheet.pdf

https://wch.github.io/latexsheet/latexsheet-a4.pdf

[Polymer]

Thank You Chemelec & Nupi for your replies!
I now understand and calculated a similar number with k=1 Yippee ...

For future reference: it is called "mutual inductance"

Most pages I found did not show how to figure out M, so I'll jot it down here:

M = k times square root of (L1timesL2) How the hell do I get math notations in here?

k can be from zero to one. k=0 is no mutual inductance & k=1 is complete mutual inductance.
I used 1 for the NUPI coils on ferrite core and got 3384uH as the result.

SERIES INDUCTORS WITH MAGNETIC COUPLING
When two inductors in series are so arranged that the field of one links the other, the combined inductance is determined as follows:
Ltotal = L 1 + L 2 + 2M

Hope this is understandable.

Happy Tinkering

[Nupi]

Hello Nupi,

Thank You for your reply.

I will be trying different ferrites once I get them and new wire ( I have ran out).

One thing has puzzled me for a while, but I never asked. It is regarding L1 (1600µH) + L2 (330µH) = 3300µH in your wonderful drawing.

Are not Inductive things added in series? Like the result should be 1930µH ~ 2mH.

What have I not understood here

Thank You Nupi,

Hi Polymer,

"Are not Inductive things added in series? Like the result should be 1930µH ~ 2mH."

That is correct if they are connected in series and have no magnetic interconnection with each other. But in the pinpointer the coils do have a magnetic coupling with each other.

SERIES INDUCTORS WITHOUT MAGNETIC COUPLING
Ltotal = L 1 + L 2

SERIES INDUCTORS WITH MAGNETIC COUPLING
When two inductors in series are so arranged that the field of one links the other, the combined inductance is determined as follows:
Ltotal = L 1 + L 2 + 2M

On this website I think they explain in an understandable way how it works.
Regards, nupi.

http://www.electronics-tutorials.ws/inductor/series-inductors.html

[chemelec]

It Doesn't Work that way, When Both windings are on the Same Ferrite.
Or also when Two Inductors are placed Close Together.

[Polymer]

Hello Nupi,

Thank You for your reply.

I will be trying different ferrites once I get them and new wire ( I have ran out).

One thing has puzzled me for a while, but I never asked. It is regarding L1 (1600µH) + L2 (330µH) = 3300µH in your wonderful drawing.

Are not Inductive things added in series? Like the result should be 1930µH ~ 2mH.

What have I not understood here

Thank You Nupi,

[Nupi]

Hi, Polymer.
I'm doing well, thanks.
I am now busy with other things.

"Does anyone else happen to have this problem?"

I do not know if it's a problem if you looking for a good thermometer then it's a blessing.
I have also slightly affected by but not extreme.
I'm not sure but it would also be the type of ferrite that you are using.

[Polymer]

Hmmm, not much happening on this thread, NUPI - I hope you are doing well!

I have been using the NUPI PP out in the field a while now and ran into a very annoying situation.
The PP would be "out of range" and could not be externally adjusted to the most sensitive point anymore.
My original tests inside and outside were fine before. I have now found out what the "problem" is.

I have a very sensitive NUPI Thermometer now
Heck, my original testing was done when inside temperature = outside temperature.
It took me a while to nail this bugger down, I thought it was maybe magnetic or something going wonky with the pcb at first.

I did temperature testing in relation to the most sensitive point from 0°C to 50°C with the adjustment pot.

Gosh was I surprised
I have an offset of 480 Ohms per °C for the 3 ferrite PP and
340 Ohms per °C for the single ferrite one!
It looks linear to me.

I would have liked to have used a linear PTC resistor as a quick easy fix.
Finding PTC Resistors with such a high temp. coefficient was not easy
or putting many in series is out of the question, because the
base value would be to high to use in this circuit. What a bummer.

I have now opted to have two external pots, same one for fine adjustment (2k) and one for
temperature adjustment (25k).

Does anyone else happen to have this problem?

I still highly appreciate the NUPI PP, especially for its simplicity, depth of detection and changing beeping frequency to depth/size of target.

Temperature drift seems to be an issue in electronics, but I couldn't find all to many posts about it here.

Happy Tinkering.

[ionut_mtb]

yes is very hard, i have 5 months contract far from family and friends. i will try to make nupi for diving, i have few ideas and i will share after i will make. one for diving and one normal, for helping the big metal detector. i made surf pi pro, is very nice, stil have some issues wich i will put on the right area of the forum, but i'm glad is working. (resonable) i want to buy a comercial MD so i can register in my country. home made MD cannot... i need invoice for register. i was thinking for teknetics eurotek pro DD11inch since i'm beginer in this hobby.
good day!

[6666]

Hi ionut_mtb
Great job you have, very hard work if you are crew, I was there on Pacific Jewel and Pearl, NEXT time I'll pack at least the pinpointer, and have a bit of a look on the beaches which are amazing to swim at.

[ionut_mtb]

i'm working on cruise ship(carnival legend). i i've been almost everywhere, but isle of pines... amazing!

[6666]

Hi ionut_mtb
they look like lead projectiles,
I was on Isle of pines twice last Sept / Nov last year 2014
beautiful place, would loved to have had a MD with me.

[ionut_mtb]

lead bullet... not sure

[Polymer]

[ATTACH]33011[/ATTACH]
isle of pines, new caledonia. i dont have small findings. it was very nice.

Nice to see your type of finds.

What are are those nine flat-ish lead looking things ???