50/60 Hz passive detecting system

[rmarchesi]

We are trying to develop an economic portable system to detect ELF magnetic fields. We would like this device be able to detect fields as low as 5 to 10 mG and if possible we would like to avoid active components to amplify the signal, because this system is addressed to people that are terrified by magnetic fields.
We have made an antenna with 200 loops, that gives 5 mV AC for a 10 mG field. The question is: which is the best way of alerting someone with such a low power signal? Even ammeters needles would move too little to show 5 mV. LED's require minimum 2 V and 20 mAmps. Any idea? Would a step up transformer work? Thank you.

 

[Skogsgurra]

Best advice: Tell them that ELF isn't harmful.

Supporting such superstition isn't an engineer's task.

Making money out of it is shameful.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[IRstuff]

Don't forget that you actually need 3 orthogonal coils to correctly determine field strength AND directionality

TTFN

FAQ731-376

 

[IRstuff]

My druthers would be a nice digital display, showing field strength and directionality, based on something like this:

http://www.honeywell.com/sites/serv...t?docid=D6DFF41B2-EB82-8437-91D3-16A123A03E1A

or this:

http://www.ssec.honeywell.com/magnetic/datasheets/HMC5843.pdf

which does all 3 axes and outputs on I2C bus.

The first one is way more sensitive, and may be in higher demand for those who are particularly paranoid. You wouldn't be able to make coil-based system small enough; it'll be so noticeable that they might as well wear their tinfoil hats in public...

TTFN

FAQ731-376

 

[rmarchesi]

Thank you guys, for your answers.

Gunnar, I know we live in an environment that is completely full of waves, and we live without so many problems, but some people say the can 'feel' the fields. What should we do? Help them in feeling more protected or just leave them with no help?
This is s link to the WHO EMF program.

http://www.who.int/peh-emf/en/

IRstuff. Thank you for your links, but from a first look I have the impression that those sensors are for static field (Earth's magnetic field) and not for variable fields, like the one generated by 50 Hz.

Riccardo

 

[Skogsgurra]

If you, like me, had been through all the phases of belief, fear, doubt, experimentation, insight, discussions, statistical tests, research, article writing and, finally being completely convinced that there is no danger whatsoever with ELF magnetic or electrostatic fields in the few gauss order of magnitude, then your only reason to do anything about the "problem" is based on commercial desire to make money out of people's fear.

I am strongly against that.

BTW, a 200 turns loop is just moot. It does work if you use a low power opamp. But if you are afraid of the magnetic fields created by the current consumption (ten - twenty microamps) then you need many more turns. What about a few thousand turns and a large area loop. That will produce enough power to light a red (red needs the least voltage) high efficiency LED. But the current in such an LED will be in the mA order of magnitude. That's a lot more "dangerous" than the 20 microamps that an opamp needs.

One question: Are you an electrical engineer? Or are you dabbling outside your field of expertise? Please read the site rules.


Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MagnetDave]

Do you have any literature on this? I would like it when I am discussing people who want to use refrigerator magnets for joint pain, and are convinced of the value of low magnetic fields.

I have been considering your project, and my feelings rhyme with "spoondoggle." If you can't just throw together some diodes to make a full-wave rectifier, then I'm inclined to tell the client "look, there are no electronics that exist that demonstrate the 'issue' without making it worse. I look forward to reading your manifesto in the paper."

 

[Skogsgurra]

Dave

You addressing whom?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[IRstuff]

rmarchesi,

The devices have bandwidths of 10 kHz, and are more than capable of sensing a 50Hz field. The processor that you'd need for processing the data can threshold and filter the data to look for anything you want.

You have a similar problem with the wire loop, as there is no discrimination in the wire loop for any specific frequency, so if there are high-frequency AC sources nearby, it'll detect them also.

TTFN

FAQ731-376

 

[MagnetDave]

Skogsgurra,

That was directed to rmarchesi.

 

[rmarchesi]

Dave, there is plenty of literature on the web. In the past we have shielded a part of an hospital where they treat patients with magnetic fields. I'm not a doctor and I can't judge.

 

[Skogsgurra]

The quality of that literature is rather poor - to say the least.

Investigations made by national and medical research institutes in most civilized countries have shown that ELF magnetic fields have no effect whatsoever on animals or humans.

But, it is a free world (mostly) and there are lots of people that THINK that they are sensitive to magnetic fields and are eager to tell the world about their problems.

In on hospital in Sweden, a whole building was shielded because a group of patients demanded it and the doctor was too busy to find out if there was any scientific reason for it. I guess that that happens all over the world - but that doesn't mean that the 'problem' exists outside certain individual's brains.

My first studies on this 'problem' are from 1986. For 24 years, no evidence - other than different persons subjective feeling - has been presented. Au contraire, every serious and well documented study has falsified the theory about ELF magnetic fields in the gauss or millitesla range having any effect on humans or animals.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[IRstuff]

I wouldn't even begin to try and claim that there is zero magnetic effects. There are those that supposedly have differentiation in color receptors and can see shades of color that the majority cannot. Perhaps they are an evolutionary offshoot. Likewise, there may indeed be other evolutionary offshoots that can sense magnetic fields.

Since these are ostensibly few in number and may not be fully aware of their abilities, studies of any kind would no doubt result in inclusive answers.

Regardless, we as engineers often are required by our contract commitments to design and build things of dubious value, so why not magnetic field sensors?

TTFN

FAQ731-376