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30th May 2017, 8:50 pm | #1 |
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,320
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Magnetometer.
I've got this vintage germanium PNP transistor circuit which claims to be a magnetometer.
No idea how sensitive it would be, but more to the point is it likely to work at all? I know there are more modern designs, but thought this one looked like nostalgic fun to reproduce as I have all the parts apart from the coil - which I'll have to improvise. As far as I can see it's a conventional audio amp up to Q3, and I'm guessing D1 sets the bias on Q4, Q5 although I'm not sure the latching circuit would work. I guess a diode across the relay would be s sensible addition too. Not sure where I'll get that 10k pick-up coil! Any thoughts? Thanks, Ian |
31st May 2017, 10:53 am | #2 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Magnetometer.
It will detect an AC magnetic field. If you wave it around fast enough it might even detect a constant field. No idea how sensitive, but I suspect not too good. It is essentially an audio amp feeding a relay, with a latch to hold on a buzzer when the threshold has been reached.
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31st May 2017, 7:41 pm | #3 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,190
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Re: Magnetometer.
There was an interesting project in Practical Electronics in the early 1970s entitled 'Proton Spin Magnetometer'. Apperently it detected small changes in magnetic fields by flipping the spins on the hydrogen nuclei in water. IIRC it was all discrete transistors and didn't look that complicated.
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31st May 2017, 8:26 pm | #4 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Magnetometer.
I remember the picture of a wooden beam with a plastic bottle at each end.
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31st May 2017, 8:35 pm | #5 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Magnetometer.
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1st Jun 2017, 9:18 am | #6 | |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
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Re: Magnetometer.
Quote:
Yes, the project was in the October 1970 issue and I built this magnetometer about 13 years ago but didn't get around to winding the two detector coils which are mounted on the boom which is carried. I would like to try and complete this as it's one of many unfinished projects. I'll have to locate the magnetometer and take a few pics. Regards Symon. EDIT: Just noticed Lawrence's link to the article Last edited by Philips210; 1st Jun 2017 at 9:20 am. Reason: Additional text |
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1st Jun 2017, 10:01 am | #7 |
Octode
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,782
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Re: Magnetometer.
In the 70's I worked in the Electronics workshop of the Physics dept at Bradford Uni. Our main interest was Geo Physical Surveying. This involved developing instruments to survey archaeological sites. Various instruments were developed, including the Earth Resistivity meter, Flux gate Magnetometer, Proton Magnetometer and the Induction loop Instrument.
The item mentioned above, was an Induction loop detector, which although portable is probably the worst instrument for serious survey work. The other two types, Resistivity and Magnetometers are for different types of survey. Resitivity, measures as you would expect the resistance of the soil under two probes, with another two probes sited well away from the survey area. It is in effect a wheatstone bridge, with one current probe and one voltage probe, in each area. The current was 1 Khz at 5 m/A a constant current generator. The voltage was measured with a syncro rectifier, and we could measure resistance up to 1K, down to 10R FSD . The magnetometers were designed to measure magnetic differences, such as in Burnt hearths , metal working areas, pottery kilns etc. The induction loop instrument, was developed as a differential loop instrument to vastly increase its sensitivity, and with phase detectors, could identify, ferrous / non ferrous, metals, and non metalic. However to balance the null, was very difficult, and was abandoned in favour of fluxgate and proton magnetometers All these instruments were developed to a high degree of sophistication "for the time". However with the much improved semiconductors of today, these instruments are now very sophisticated.
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Should get out more. Regards Wendy G8BZY |
1st Jun 2017, 11:26 am | #8 |
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,320
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Re: Magnetometer.
Excellent posts everyone. Thanks for the input and links.
Ian |
2nd Jun 2017, 10:11 am | #9 |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
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Re: Magnetometer.
Hi.
A few pics of my Proton Magnetometer built using 0.15" matrix board yet to be completed. Regards Symon |
2nd Jun 2017, 10:13 am | #10 |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
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Re: Magnetometer.
A couple more pics of the magnetometer.
Symon |
2nd Jun 2017, 11:49 am | #11 |
Pentode
Join Date: Jul 2015
Location: Newbury, Berkshire, UK.
Posts: 243
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Re: Magnetometer.
Simon, your project looks interesting, What kind of coils you need ?
I also have a long list of unfinished projects, for example a cosmic ray detector. A year ago I bought a lot of GM tubes, planning to stack them in 4 layers, than make a display looking like 4d led cube. I wish we had a new discussion chapter like "My projects 'on hold'", about what we are planning, but can not start for different reasons... Thank you, Jacek. |
2nd Jun 2017, 12:38 pm | #12 |
Nonode
Join Date: Aug 2010
Location: Resolfen, Wales; and Bristol, England
Posts: 2,588
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Re: Magnetometer.
I'd like to have such a thread, but in my case it'd be filled with projects I started but haven't finished.....
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2nd Jun 2017, 9:06 pm | #13 | |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,562
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Re: Magnetometer.
Quote:
The detector coils each comprise 750 turns of 24 s.w.g. enamelled copper wire wound on a plastic pill container. This is filled with distilled water. Details of these coils can be seen in the article that Lawrence provided the link for in post #5. Part of the reason for not completing the project was due to not being able to locate suitable pill containers. It shouldn't be difficult to use a modern size container and make slight alterations to the number of turns to achieve a similar inductance, typically 21mH. The original Mullard Vinkor pot cores used in the main amplifier and the meter amplifier were obviously not available when I built the project. I used the RM series with adjuster and made slight modifications to the windings. I'll have to locate my notes to check on this. It was a very interesting project to build and I would like to get it completed. Practical Electronics had some good ideas and novel projects back then and I'm sure many of their circuits are still worth building even now. Regards Symon. |
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3rd Jun 2017, 3:22 pm | #14 |
Octode
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,782
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Re: Magnetometer.
Symon. Nice one.... Our development in 1973, lead to using Phase locked loops to detect the minute signals from the coils, as my attempts at building narrow tuned amps was abysmal. Each output was then squared and processed digitally...... Oh for micro controllers then.........
One of our colleagues.... went on to form Geoscan Technologies, whom supplies the world of archaeology and other agencies with the above types of survey equipment. Happy experimenting.
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Should get out more. Regards Wendy G8BZY Last edited by Wendymott; 3rd Jun 2017 at 3:23 pm. Reason: Typo |