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Offline olsteffeTopic starter
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« on: July 31, 2009, 04:28:09 pm »
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In the progress of purchasing and building FGM 3 type gradiometer but see that some state that the gradient resolution will not be better than 100 nT. Any comments?

What I have dug up on different homepages of people using it in a magnetometer mode is that the sensitivity/accuracy of the sensor is giving you a resolution of a few nanoteslas. To me this indicates the possibility of obtaining a resolution of a few nanoteslas far better than the 100 nanoteslas mentioned.

Thought i should add this link to an excellent primer on sensor accuracy, sensitivity and resolution;

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Offline Eugene52
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« Reply #1 on: August 03, 2009, 01:01:53 am »
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Quote:Posted by olsteffe
In the progress of purchasing and building FGM 3 type gradiometer but see that some state that the gradient resolution will not be better than 100 nT. Any comments?

What I have dug up on different homepages of people using it in a magnetometer mode is that the sensitivity/accuracy of the sensor is giving you a resolution of a few nanoteslas. To me this indicates the possibility of obtaining a resolution of a few nanoteslas far better than the 100 nanoteslas mentioned.

Thought i should add this link to an excellent primer on sensor accuracy, sensitivity and resolution;

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http://archive.evaluationengineering.com/archive/articles/1298pct.htm






Hello Olsteffe .  Welcome to Thunting.com . We have a small Magnetometer Project area here on this forum , scroll down the message boards to the "Tech Talk" area .. I started a few posts several months ago but got side tracked with Metal Detector Projects . I sent you a PM about a 3.5 mb pdf file I want to send you . I Hope you check back everyday on our Forum , and also post information on Magnetometer Circuits.........Thanks for joining us !!!
Best Regards.........Eugene

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Offline olsteffeTopic starter
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« Reply #2 on: August 05, 2009, 04:42:39 am »
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Thank you Eugene52. Some good information on sampling by period counting, should give excellent accuracy.


Ooops! that should be resolution Teach. Hard to stop mixing them up Cheesy.




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« Reply #3 on: August 09, 2009, 07:05:16 pm »
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Just found some information on the sensitivity of the FGM-3 sensor. The sensitivity is close to .9 Hz/nT.

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« Reply #4 on: August 17, 2009, 01:41:53 pm »
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goldigger or other electronics wizards.
Seems as if this sensor has had its fair share of interest, found this schematic on the net reverse engineered by someone.
I understand that this is some type of square wave oscillator. The sensing element is based on the earth field changing the inductance of the coils thereby changing the output frequency. I guess the diode is for countering the back emf of coil.
Is there a possibility that someone could give an explanation of the circuits functioning and its capabilities.

olsteffe


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« Reply #5 on: August 18, 2009, 03:45:33 am »
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olesteffe;

Ah, we have awakened  the (magnetometer-) sleeping giant.  Great

Interesting , are the coils in parallel, do you know?

I would say the diode is for dampening the pulse, yet any signal return will be lower in voltage than the diode "barrier" voltage of 0.7 to 1 v... similar to placing a diode across  a relay coil.... the second coil probably has a larger number of turns.

personally, I don't know why, but I would prefer a PNP version with one end of the coil grounded... helps prevent power supply accidents, and takes fewer parts.... I think.

Of course, what is not shown, could be interesting, too. Was there any literature, with this?

goldigger

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« Reply #6 on: August 18, 2009, 02:04:25 pm »
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Goldigger, sorry that is all there is  Thumbs Down. But I have found an interesting hands on magnetometer design article on an astronomy site. It is a build from scratch sensor with suggestions for a working magnetometer schematic. It is written under the guidance of the late Guru  Pray Jack M. Janicke. It is downloaded, but unfortunately not the URL.
Seems as if the Speake and Stefan-Mayer sensors are "copies" or at least very much based on this design.
Eugene52 Copyright or left  Grin I could upload it to the download section Huh?

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« Reply #7 on: August 18, 2009, 03:48:50 pm »
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Quote:Posted by olsteffe
Goldigger, sorry that is all there is  Thumbs Down. But I have found an interesting hands on magnetometer design article on an astronomy site. It is a build from scratch sensor with suggestions for a working magnetometer schematic. It is written under the guidance of the late Guru  Pray Jack M. Janicke. It is downloaded, but unfortunately not the URL.
Seems as if the Speake and Stefan-Mayer sensors are "copies" or at least very much based on this design.
Eugene52 Copyright or left  Grin I could upload it to the download section Huh?


Hello olsteffe . Am I in trouble for posting "copyright material" that is posted all over the internet ? I am glad you are helping with Magnetometers here on this Forum . I am not an expert yet on Magnetometers but I know they work . I have been reading some mining Magnetometer surveys/Grid readings from Nevada and I trust what I see .......On another note , I have never seen an "LRL" that works yet !!
Thank-You again for your posts .
HH..... Great....Eugene

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« Reply #8 on: August 19, 2009, 03:38:00 am »
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As you all have noticed, the files are uploaded to the download section  Great

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« Reply #9 on: August 23, 2009, 09:19:59 am »
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olsteffe;

Hi, I ave been away, for 2 days and have masses of stuff to go through, or would have replied in a relative way, relativistically speaking... your info is interesting and I guess I will have to bite the bullet and look at the download section, which I have been avoiding!

Jack M. Janicke sounds familiar, however, he was not a Guru, in anything I am  into.... I think? Perhaps you will enlighten me? Nor do I know Speake and Stephan-Mayer.... I have been working in isolation, based on information obtained, several years ago, which now seems in error, so I have had to re-group and re-design, as I got some data, in a PDF, back in June, from a university project, in INDIA! From that, I have come up with a new design and an interesting development, which I would like to share, but will not, until I can check it out and try to publish it SOMEWHERE where I can get credit for discovering it! Until that time, it is just a teaser! I am not even going to give a hint!  Funny

I have been off, playing with pc board software..... and not achieving much, yet. No no!

I am FINALLY getting ExpessPC to work, although I am not crazy about it AND it does not produce a gerber file! So I keep looking.

Brian



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