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Offline goldigger
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« Reply #10 on: August 10, 2009, 02:14:14 am »
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olsteffe, kayakpirate;

I have been following this series of postings, with some interest.... now I have a question: are these Hall effect devices linear or digital? I mean, are they of strictly on/off function, or do they have a linear, gradual change in voltage/current??? Can they be biased similar to CMOS?

3 mv/V/G would indicate, to me they are linear. In that case, amplification should produce wonderful results, or would you be just amplifying error? Also, are they high impedance, voltage devices or are they low impedance, current devices??

kayakpirate, can you upload a PDF on the 3mv/V/G device??

It is my observation, if you have 1 or 2 devices, a bubble level will be needed, initially, and an inertia measuring chip (its output recorded in parallel to the Hall devices) for correction on the course of travel??

I was a lot happier with a single axis! All I need to know is: if a change has occurred, how strong it is, then log it along with GPS: multiple axes cause multiple head aches.

My purpose/need is to survey a largish area of placer claim (gridded) with the need to find concentrations of subterraine magnetite. (my spell checker does not like subterraine!) The more sensitivity, the better. I do not actually need to LAY out a grid, just use GPS data every 1, 2, 5 or 10 metres.

Olsteffe, I hope your English is good, at least enough to tell the English /up, to, of, off/ apart, because I know Norwegian has similar words used in similar fashion and it can be confusing. As you can see, I used most of those words.  Funny

goldigger

I will have to do some thinking!


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« Last Edit: August 10, 2009, 02:15:52 am by goldigger »
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Offline kayakpirateTopic starter
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« Reply #11 on: August 10, 2009, 01:05:51 pm »
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goldigger, help me with some schematics, I'll help you with your spelling.  Grin (subterranean)

The Honeywell HMC1001 single axis & 1002 dual axis is the most sensitive. The second choice would be the HMC1021 single axis & 1022 dual.

Here is a schematic showing a simple gradiometer using the 1021. I emailed the design engineer at Honewell and he told me "Using the HMC1022 or HMC1021 parts is less sensitive,(than the HMC1001) but simpler to use from a set/reset circuit perspective."

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http://www.magneticsensors.com/applications/gradiometer.html


data sheets. 

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http://www.magneticsensors.com/datasheets/hmc1001-2&1021-2.pdf


Interesting page on magnetic sensors.     

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http://www.magneticsensors.com/datasheets.html


I also just found this today. Interesting.     

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http://www.magneticsensors.com/datasheets/HMC6042.pdf


I'm also a gold prospector.
   

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Offline olsteffe
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« Reply #12 on: August 10, 2009, 02:55:56 pm »
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kayakpirate and goldigger you are two of a kind and you can not turn off your detectors  Wink. Are we up to the task of building a gradiometer Huh? think that covered it.

I am thinking  Funny
3 mv/V/G;
Sensitivity: If the sensitivity is defined as  3.0 mV/V/gauss, in the presence of a 1
gauss magnetic field with 3 volts applied
to the sensor, the output of the sensor
will be 9 mV. If in the presence of only
0.5 gauss magnetic field (erth field), the output of
the sensor would be 4.5 mV.

It is my understanding that they are magnetostrictive sensors in a wheatstone bridge, which indicates they are linear.

This indicates a output of 24,3 microV at its highest sensitivity 2,7 nT
If we increase the applied voltage (to 12 V) we will see this number improving fourfold putting less strain on the op amp (less noise) datacapturer or meter.

I hope i am not totally out on a field with my conversions  Rider if that is the case please  Teach and do not  Violent or  Idiot me.





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« Reply #13 on: August 11, 2009, 03:07:43 am »
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kayakpirate;

No, my spelling is not wrong, I guess you never heard of a terraine..? It is an application of a common word with a spelling variation, to distinguish it, actually it could be considered a technical term in geology and I, perhaps, should not have used it in the sense I did. Oh well.... Having brain damage has its compensations.

Interesting circuit, I think it may be simplified and temperature compensation should be easy enough. I really do not like the LM324, I can sub two LF353's and space things out a bit. If and when, I really do understand the circuit, I would make some changes. Also, more information (lacking) would be needed for temperature compensation.

I noticed one other thing, there is no mention of how far apart the sensors should be, if its even necessary, and no mention of orientation, of the sensors.....  guess I will have to read the PDF, twice. I found this effect works: the first time -  "yeah, good chip.;" second time "hey, this is simple." It seems like the first read registers, sub consciously, and a second read, some time later, cues the subconscious stuff, so I really DO understand it.

Gold prospector, hmmmmm, well.... basically I prospect for anything but asbestos. Even that has other, valuable, things associated with it, like jade.  I have 5 mineral claims and one placer claim. I had 3 more placer claims, that I just did not renew, this August, because I physically and financially can not handle them, into the bargain, my partner died July 4, of cancer related kidney failure. Not much point in hacking at it alone. (He owned the machinery, I own the brain.)

Ok, I will study the PDF's ant the nice schematic, but first I go talk to olateffe. Or as the famous Danny Kaye movie went (The Inspector General) "But first vee danze!"

By the way, I was top in my class(es) in spelling, but a car accident left me with some dyslexia and memory twists.... you know - "its in the dead zone!"

goldigger



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« Reply #14 on: August 11, 2009, 03:41:31 am »
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olesteffe;

Very interesting! BUT, is  this thing a gradiometer or a magnetometer.... if it measures gradients of a magnetic  field, is it not still a magnetometer??  No no!

Or am I splitting already fine hairs??

I got some stuff from kayakpirate, which I need  to consume and ruminate on.... the circuit, I downloaded (never noticed the supply voltage) has a gain of 210.5 (1 meg/4.75k) and if  (based on what you are saying,) I use 15v, then an Av of 133.3333 will give a 6 volt output (15 v, if it does not exceed ratings, to the sensors, 12 to the amps) so then I would use some resistors to get 2.5 v to feed my ADC.... with a 6v output, it can go +/- about 5.5 v (not likely, but centered, anyway. For neatness?)

OK, now, I have another small... um.... thing?... to discuss: If you take a perfectly square, thin sheet of metal, copper is good, and ground one corner, feed a low current, into the opposite corner, the current (note, current, not voltage) at the other two corners are equal, in the absence of a magnetic field. Change or introduce a magnetic field and the corners become out-of-balance, in respect to current.  Wise

This  should work, similarly to  a Hall effect device, with the corners fed directly to the respective bases, of similar, or if  you can not adjust for  balance, a matched pair of transistors, to act as current converters, like 2-MPS-A13's, with a current gain of 1000. It would, in effect, be a giant Hall device.  Mad

With double sided pc board, you could have 2 sensors, at 180 degrees.... one vertical, one horizontal.  Detecting

Do you think it could be sensitive enough? You would need the lightest grade of copper possible... 0.5 ounce per square foot is, so far, the lightest commercial stuff that I have seen.

Maybe it would just be a Rube-Goldberg machine?Huh?  Funny

goldigger



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« Reply #15 on: August 11, 2009, 11:25:50 pm »
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I asked the Honeywell engineer about the spacing on the sensors but he didn't answer me.
It seems to me that most magnetic locators have them about 20" apart. I think the farther apart you put them the more sensitivity you will have but aligning them would be a problem.
 That 6042 chip isn't sensitive enough, something like 125nt, it is also very small, you would have to solder with a needle.

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« Reply #16 on: August 12, 2009, 12:26:11 am »
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Quote:Posted by kayakpirate
I asked the Honeywell engineer about the spacing on the sensors but he didn't answer me.
It seems to me that most magnetic locators have them about 20" apart. I think the farther apart you put them the more sensitivity you will have but aligning them would be a problem.
 That 6042 chip isn't sensitive enough, something like 125nt, it is also very small, you would have to solder with a needle.



kayakpirate;

what did he say about orientation?

Place a pair of each in in their individual holders, oriented as they are supposed to be and use the second pair for error correction, something like stereo??  Buffer the correction pair with lots of capacitance and just use the slow alteration component. Have the input of  the sensors go to the non-inverting, individual inputs, of the op amps (as the circuit shows); apply the correcting component, including temperature, to both inverting inputs, so both amps are affected equally.

Something like that. The vertical corrective component could be applied to just the vertical sensor amp and same with horizontal??? I thought averaging might be effective.

goldigger



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« Reply #17 on: August 12, 2009, 09:33:58 pm »
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 He never said anything about orientation. I asked him a bunch of questions and he only half answered one.  Maybe next time I'll tell him I'm with Microsoft or Garmin. Then I bet he will have all the answers. lol

I cheated and bought a hand held mag. It's a toroidal sensor type with lcd readout and speaker. It should be here next week.

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« Reply #18 on: August 13, 2009, 05:02:04 am »
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kayakpirate;

Tch! Its nice to have money!  Funny

I will look for a cheap chip source, that is not too complex, for me, to access, and I will check Jameco and Digitek, both.

Meanwhile, did you read my post about copper pc board, used as a giant Hall effect device?? The more  I think about it the more I want to play with it. I have some MPS-A13's to act as current gain amps, also it would not need to be set and reset, like the chips, as copper is non-magnetic. That may be the real drawback, with those IC's.

I can see it now, a foot square piece of pc board as a search device, instead of a coil.

 Detecting

What happened to olesteffe??

goldigger



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« Reply #19 on: August 13, 2009, 02:05:35 pm »
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Nice to be missed Golddigger

"Very interesting! BUT, is  this thing a gradiometer or a magnetometer.... if it measures gradients of a magnetic  field, is it not still a magnetometer??"

Well it is actually two magnetometers measuring the deflection of the earth magnetics field, by an anomally, at two different positions. The gradiometer naming is just a description of the setup.

I have thought about your Hall device and based on the equation for a Hall device the effect (voltage) is a result of the flux B, the current fed to the device and the thickness of the substrate. I believe what you would achieve by making it bigger is that it will be able to handle more current and this would only compensate for the lack of thinnes of the device. But this is only my thoughts.

By the way, have you tried the simple experiment with a soft non magnetic iron bar and a compass to see how the earth field can be visualised and used to magnetise iron?


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