A Magnetic Field Question Re Gauss Level of 4.7

Hello ATS.

I have recently started to conduct of few radio frequency experiments in my home and just to be sure that there was no magnetic interference nearby, I conducted a test of my workspace using Gauss meter.

One of my workbenches is constructed from stainless steel, not unlike this item here,Link

Whilst conducting my test, with only low level readings around most of the room, I suddenly had a reading of over 4.7 Gauss on one corner of my worktop.
Now I must admit that I know very little about the effects of Gauss levels but I would be interested to know the following:

1) Is a Gauss level of 4.7 considered high and if so, does this have safety implications?
2) What could possibly cause a small area of my workbench to attain this level?
3) Could this level affect radio frequencies in any way?

I look forward to any replies and thank you for your time.


Further addition: One small area on the side edge of the worktop measures 6.5 Gauss, could this be magnetic residue from an electroplating process during manufacture?

a reply to: studio500

1) Yes. Very high. Do not stand between such a field and anything magnetic, you will be speared from across the room.
2) Error in gauss meter. Otherwise some people building MRTs would like to speak with your workbench..
3) No.

a reply to: ManFromEurope

Thank you for your quick response!

I've just added a little extra to my op but will paste it here too regarding an area that reads 6.5.

Paste: Further addition: One small area on the side edge of the worktop measures 6.5 Gauss, could this be magnetic residue from an electroplating process during manufacture?

I have just read a little section about MRI fields and protection that should be in place for a Guass field of 5.

I think I should try to obtain another meter just to check if the reading is correct or if the meter is faulty as you suggest.

Just to provide further information, these readings do appear to be very localized to small areas on or near the bench.

The readings and areas can be seen in the image below. The field areas do not appear to extend very far around the main points of high reading, which I suspect is a good thing.

originally posted by: studio500
1) Is a Gauss level of 4.7 considered high and if so, does this have safety implications?

Whether it's high or not depends on what you're trying to do. If you had that near an MRI that operates at 70,000 gauss, then 4.7 isn't much compared to 70,000.

However there are other types of MRIs that work on fractional gauss and so if you're measuring milligauss, 4.7 is huge compared to milligauss.

This page says MRIs operate at up to 700,000 gauss but I'm wondering if that's a typo because I thought it was up to about 70,000 gauss:

Gauss

Typical values

10−9–10−8 gauss – the magnetic field of the human brain
10−6–10−3 gauss – the magnetic field of Galactic molecular clouds
0.25–0.60 gauss – the Earth's magnetic field at its surface
25 gauss – the Earth's magnetic field in its core[4]
50 gauss – a typical refrigerator magnet
100 gauss – an iron magnet
1500 gauss - within a sun spot [5]
10000 to 13000 gauss – remanence of a neodymium-iron-boron (NIB) magnet[6]
16000 to 22000 gauss - saturation of high permeability iron alloys used in transformers[7]
600–700,000 gauss – a medical magnetic resonance imaging machine

Whether the MRI is 70,000 or 700,000 gauss, I think you are advised not to get such an MRI if you have any metal implants in your body.

By the way, gauss is no longer the current unit in SI which is tesla, 1 tesla=10,000 gauss.

a reply to: Arbitrageur

I misunderstood Gauss vs. Tesla.

Sorry, OP, your Gaussmeter might check out ok.

a reply to: ManFromEurope
Oh yeah, 4.7 tesla would be huge.

I forgot to answer the part about affecting radio signals. I don't think the static gauss reading will, but the table itself might have some effect.

If you build a metal enclosure called a faraday cage, it will actually block radio signals from entering the enclosure.

That table isn't a complete enclosure so it won't have a complete effect of a Faraday cage but it could have some effect. If you were doing sensitive experiments with radio you might be better off using a non-metal table, such as wood, or plastic since they don't have a lot of highly mobile electrons that can be affected by EM radiation, as happens with metal.

originally posted by: Arbitrageur

originally posted by: studio500
1) Is a Gauss level of 4.7 considered high and if so, does this have safety implications?

Whether it's high or not depends on what you're trying to do. If you had that near an MRI that operates at 70,000 gauss, then 4.7 isn't much compared to 70,000.

However there are other types of MRIs that work on fractional gauss and so if you're measuring milligauss, 4.7 is huge compared to milligauss.

This page says MRIs operate at up to 700,000 gauss but I'm wondering if that's a typo because I thought it was up to about 70,000 gauss:

Gauss

Typical values

10−9–10−8 gauss – the magnetic field of the human brain
10−6–10−3 gauss – the magnetic field of Galactic molecular clouds
0.25–0.60 gauss – the Earth's magnetic field at its surface
25 gauss – the Earth's magnetic field in its core[4]
50 gauss – a typical refrigerator magnet
100 gauss – an iron magnet
1500 gauss - within a sun spot [5]
10000 to 13000 gauss – remanence of a neodymium-iron-boron (NIB) magnet[6]
16000 to 22000 gauss - saturation of high permeability iron alloys used in transformers[7]
600–700,000 gauss – a medical magnetic resonance imaging machine

Whether the MRI is 70,000 or 700,000 gauss, I think you are advised not to get such an MRI if you have any metal implants in your body.

By the way, gauss is no longer the current unit in SI which is tesla, 1 tesla=10,000 gauss.

Thank you for the input Arbitrageur, it makes for interesting reading and comparison.

The reason for undertaking the readings came about when testing radio reception whilst using a copper antenna wound into a circular configuration. I noticed that when the antenna was placed on one spot on the workbench, all reception was lost but resumed upon moving the antenna to a different location.

This was at my initial test phase which would not normally have been conducted on the steel bench for obvious reasons.

The meter which is admittedly a few years old (hence the reading in Gauss) was my late fathers and it could well be defective but I won't know if it is until I can locate another meter to check.

a reply to: studio500

Whilst conducting my test, with only low level readings around most of the room, I suddenly had a reading of over 4.7 Gauss on one corner of my worktop.

Your work table probably has a power strip and things plugged into it sitting on top of it? All metal objects can randomly act as antennas for EMF signals generated by ay nearby charged conductors, batteries, transformers.

Even sitting near a wall outlet or power cable running near one of the legs the all metal table can conduct and 'rebroadcast' EMF 'signals' .

Now show us a pic of your real table and whats on, under and around it.

originally posted by: Arbitrageur
a reply to: ManFromEurope
Oh yeah, 4.7 tesla would be huge.

I forgot to answer the part about affecting radio signals. I don't think the static gauss reading will, but the table itself might have some effect.

If you build a metal enclosure called a faraday cage, it will actually block radio signals from entering the enclosure.

That table isn't a complete enclosure so it won't have a complete effect of a Faraday cage but it could have some effect. If you were doing sensitive experiments with radio you might be better off using a non-metal table, such as wood, or plastic since they don't have a lot of highly mobile electrons that can be affected by EM radiation, as happens with metal.

Sorry, I posted my reply before reading your update.

Yes a Faraday cage is next on the list and an absolute must regarding my forthcoming experiments using Germanium diodes.

At least I know what areas to avoid and will seriously consider the addition of a second non conductive workbench too.

In fact, I do wonder if my experiments will be compromised as the property in which I am currently located has the upper storey level covered in corrugated iron sheeting, albeit covered in external and rendered insulation.

It makes for terrible mobile phone comms, I have to step outside every time I want to make a call :0)

originally posted by: intrptr
a reply to: studio500

Whilst conducting my test, with only low level readings around most of the room, I suddenly had a reading of over 4.7 Gauss on one corner of my worktop.

Your work table probably has a power strip and things plugged into it sitting on top of it? All metal objects can randomly act as antennas for EMF signals generated by ay nearby charged conductors, batteries, transformers.

Even sitting near a wall outlet or power cable running near one of the legs the all metal table can conduct and 'rebroadcast' EMF 'signals' .

Now show us a pic of your real table and what's on, under and around it.

Now that's interesting, there once stood a microwave oven near to this point but it has since been moved to the opposite side. As for power lines, there is a socket above the bench on the far side opposite.

I will take a photo as requested as this may help.

a reply to: studio500

Consider too, if the bench is against a wall, that AC wires probably run behind the wall too, generating further emf fields.

Like someone else suggested, a wooden table for experiments is better than metal. Adding isolation like earth ground might be helpful, too.

Playing with emf meters is fun. Your fixed signal is interesting enough, pull the table away from the wall a few feet and note the difference.

a reply to: intrptr

I myself built this room as a side extension to my property, the stud wall behind the table does have a socket as you will see in the images that I am about to post but the power cable only extends from the cavity of the sidewall on the right hand side, direct to socket.

It's a interesting idea though to move the table away from the wall and re-test. Simple and eloquent yet I never thought of doing that lol. I shall re-test shortly.

I'm just about to post the images of the bench and room.

Here are the images of the actual bench and position in relation to power outlets.





This last image shows the underside of the bench. The tape residue is roughly where the high reading starts at around 4 but increases the further the meter is moved toward the wall. The highest reading of 6.5 is on the side lip itself.



The rest of the bench reads normal including the last place the microwave once stood which was directly in front of the double socket.

a reply to: studio500

Whats sitting on the table there in the corner? I see a wire touching the table...


theres your sign(al)...

Btw, I really do appreciate everyones input and assistance here and I'm really grateful for your help.

I'm admittedly very new to the area of electronics and I have much to read and digest but I guess we all have to start from the basics.

a reply to: intrptr

That's a battery charger for a power drill.

I did think if that would have any connection but it has never sat on the area of the bench where the high readings are plus when I scanned the charger the readings were low.

originally posted by: studio500

originally posted by: intrptr
a reply to: studio500

Whilst conducting my test, with only low level readings around most of the room, I suddenly had a reading of over 4.7 Gauss on one corner of my worktop.

Your work table probably has a power strip and things plugged into it sitting on top of it? All metal objects can randomly act as antennas for EMF signals generated by ay nearby charged conductors, batteries, transformers.

Even sitting near a wall outlet or power cable running near one of the legs the all metal table can conduct and 'rebroadcast' EMF 'signals' .

Now show us a pic of your real table and what's on, under and around it.

Now that's interesting, there once stood a microwave oven near to this point but it has since been moved to the opposite side. As for power lines, there is a socket above the bench on the far side opposite.

I will take a photo as requested as this may help.

Electro magnetic field might be from the wiring in the wall that is close to that side of the table. Maybe hard to pinpoint.

ETA

Since the whole table wasn't 'hot' I am mystified....

I suppose it is possible that the energy is channeled by the table and you are measuring the energy release point of the metal?