RF absorber=conductive/needs grounding? Or not?
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This is something which has confused me for some time. When you're talkingabout shielding something from RF, I see mention of conventional shielding, which reflects RF; it is conductive.
I also see mention of RF "absorbing" material. Is this material that can literally "soak up" microwaves? But if so, can it reach a point where it's "saturated" and no longer works? I find this very confusing. And if a material "absorbs" RF rather than reflecting it, does that mean the material needs to be grounded? Here's my speculation that caused me to think of this...having been wondering how the heck to use a small Eee PC with fiber optic cable instead of highly electric-field emitting Ethernet cable (which seems like it'll be impossible or exorbitantly expensive because the Eee uses, if I'm correct, mini PCIe, and for that I'd have to convert to regular PCIe, into which I'd haveto stick an extending cable and then a PCIe based fiber optic converter card, which go from 200 to over 1000 dollars...arrrrrgh)...I started to think... ...if, ever, it were affordable to have a small laptop built to run exclusively on battery, with low voltage components, a regular sized PCI slot to use fiber optics easily, ferrite on all wires, etc., etc... ...I thought, rather than rely on a conductive metal case to keep RF inside, what about using a plastic case but coating the inside of it with RF absorbing material, or paint? That way the RF generated by the components shouldn't radiate out, but the case wouldn't have the conductivity (and thus less likely to re-radiate anything electrical plugged into it). But, it again begs the question: are all RF absorbing materials also conductive; and if so, what the heck is the difference between an absorber and a reflector? Thanks! R. |
Re: RF absorber=conductive/needs grounding? Or not?
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Yes, absorbers are conductive.
They do not saturate. They convert the energy to heat. Emil ----- Original Message ----- From: "rticleone" <[hidden email]> To: <[hidden email]> Sent: Wednesday, June 10, 2009 2:38 PM Subject: [eSens] RF absorber=conductive/needs grounding? Or not? > This is something which has confused me for some time. When you're > talking about shielding something from RF, I see mention of conventional > shielding, which reflects RF; it is conductive. > > I also see mention of RF "absorbing" material. Is this material that can > literally "soak up" microwaves? But if so, can it reach a point where it's > "saturated" and no longer works? I find this very confusing. > > And if a material "absorbs" RF rather than reflecting it, does that mean > the material needs to be grounded? > > Here's my speculation that caused me to think of this...having been > wondering how the heck to use a small Eee PC with fiber optic cable > instead of highly electric-field emitting Ethernet cable (which seems like > it'll be impossible or exorbitantly expensive because the Eee uses, if I'm > correct, mini PCIe, and for that I'd have to convert to regular PCIe, into > which I'd have to stick an extending cable and then a PCIe based fiber > optic converter card, which go from 200 to over 1000 > dollars...arrrrrgh)...I started to think... > > ...if, ever, it were affordable to have a small laptop built to run > exclusively on battery, with low voltage components, a regular sized PCI > slot to use fiber optics easily, ferrite on all wires, etc., etc... > > ...I thought, rather than rely on a conductive metal case to keep RF > inside, what about using a plastic case but coating the inside of it with > RF absorbing material, or paint? That way the RF generated by the > components shouldn't radiate out, but the case wouldn't have the > conductivity (and thus less likely to re-radiate anything electrical > plugged into it). > > But, it again begs the question: are all RF absorbing materials also > conductive; and if so, what the heck is the difference between an absorber > and a reflector? > > Thanks! > > R. > > > > ------------------------------------ > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > |
Re: RF absorber=conductive/needs grounding? Or not?
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I think a better solution would be to buy a carbon fiber skin for your laptop (if they make one for your model) that would absorb alot of Rf type radiation, you would still need to cover the screen with clearshield (very important IMO) and cover keyboard with a carbon fiber fabric.
There are imitation carbon fiber skins so you would need to make sure its real carbon fiber |
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In reply to this post by R. Ticle
Maybe others can answer this better than me. The absorbing material
I have used is conductive, and it probably reflects some of the microwaves. Stuff that can absorb a wide range of frequencies is very thick and pretty expensive (see ecosorb.com). You probably will never be able to absorb all harmful frequencies from a computer. The absorbing material might come in handy if you need to block a wireless device but can't actually disable it for some reason. An absorber converts the RF to heat. Ferrite beads convert high frequency magnetic fields to heat. If the signals are enough to heat the material significantly, then they probably do become less effective, but unless you're shielding a radar system I don't think you have to worry. I think having a metal case is a plus, because some frequencies will be reduced. But unless all seams are conductive (a pro enclosure is always welded) and the cable penetrations are all thoroughly filtered, the RF will get to the surface. It's probably more important that the electronics were laid out well, with good ground planes, good isolation or ground bonding between different boards, twisted cables... Then you still have the keyboard, mouse and screen to deal with. There are ferrite-based absorbers, and mu metal might help, but unless you have some RF or EMC engineer helping you, it's better to just stick with the basics. If the computer is really bothering you, a big thick piece of aluminum (like 1/2 inch) between you and it should do it. On Wed, Jun 10, 2009 at 1:38 PM, rticleone <[hidden email]> wrote: > > > This is something which has confused me for some time. When you're talking > about shielding something from RF, I see mention of conventional shielding, > which reflects RF; it is conductive. > > I also see mention of RF "absorbing" material. Is this material that can > literally "soak up" microwaves? But if so, can it reach a point where it's > "saturated" and no longer works? I find this very confusing. > > And if a material "absorbs" RF rather than reflecting it, does that mean > the material needs to be grounded? > > Here's my speculation that caused me to think of this...having been > wondering how the heck to use a small Eee PC with fiber optic cable instead > of highly electric-field emitting Ethernet cable (which seems like it'll be > impossible or exorbitantly expensive because the Eee uses, if I'm correct, > mini PCIe, and for that I'd have to convert to regular PCIe, into which I'd > have to stick an extending cable and then a PCIe based fiber optic converter > card, which go from 200 to over 1000 dollars...arrrrrgh)...I started to > think... > > ...if, ever, it were affordable to have a small laptop built to run > exclusively on battery, with low voltage components, a regular sized PCI > slot to use fiber optics easily, ferrite on all wires, etc., etc... > > ...I thought, rather than rely on a conductive metal case to keep RF > inside, what about using a plastic case but coating the inside of it with RF > absorbing material, or paint? That way the RF generated by the components > shouldn't radiate out, but the case wouldn't have the conductivity (and thus > less likely to re-radiate anything electrical plugged into it). > > But, it again begs the question: are all RF absorbing materials also > conductive; and if so, what the heck is the difference between an absorber > and a reflector? > > Thanks! > > R. > > > [Non-text portions of this message have been removed] |
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In reply to this post by sweetchild323
That sounds interesting; does the carbon fiber have highly conductive properties?
I once tried covering this monitor (although it's a big, conventional, 24 inch LCD) with Clearshield, and according to the AM Radio, it didn't seem tomake one bit of difference in the RF coming out. :( R. --- In [hidden email], "sweetchild323" <sweetchild323@...> wrote: > > I think a better solution would be to buy a carbon fiber skin for your laptop (if they make one for your model) that would absorb alot of Rf type radiation, you would still need to cover the screen with clearshield (very important IMO) and cover keyboard with a carbon fiber fabric. > > There are imitation carbon fiber skins so you would need to make sure itsreal carbon fiber > |
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In reply to this post by BiBrun
I just got off the phone with a technican from a company called DeviceTech;he said they have very thin RF absorber, and one type of it is non-conductive (RF to heat, as you mentioned) and can be applied with a non conductiveadhesive. He told me the typical range of absorption capability is 10 MHzto 18 GHz, with one layer perhaps 30-40 db of attenuation can be expected,more with more layers, though it eventually reaches a point of redundancy where more won't do anything.
That sounds encouraging. I explained that some people want as few emissions as possible from laptops/other types of computers...he called it a "green" market. Can you convert an electric field into heat using RF, or any kind of material? I would do a happy dance if it could be done! If I was looking at building from scratch (something akin to a laptop), what features in a screen would be the most important, EMF wise? I mean, LED lit LCD, but what about the components that make it up? What's worse and what's better? Could I stick ferrites on the cables that go to the screen? This is all so annoying, because of not wanting to use the electric field emitting Ethernet cable with the Eee PC, and it seems I can't fit fiber optic cards into the Eee PC, either. As far as building something, choosing an aluminum case would keep some of the RF in, but it would also conduct more; would this mean that any electricity from inside of the unit, even running on its own battery, would be redistributed by the case? And anything external you plugged into it? "It's probably more important that the electronics were laid out well, withgood ground planes, good isolation or ground bonding between different boards, twisted cables..." What would define a good layout? And can you further explain good ground planes/isolation...and grounding? When you say twisted cables, do you literally mean putting a twist in each cable, or twisting anything together that involves more than one cable running in the same direction? Thank you! R. --- In [hidden email], Bill Bruno <wbruno@...> wrote: > > Maybe others can answer this better than me. The absorbing material > I have used is conductive, and it probably reflects some of the microwaves. > Stuff that can absorb a wide range of frequencies is very thick and > pretty expensive (see ecosorb.com). > > You probably will never be able to absorb all harmful frequencies from > a computer. The absorbing material might come in handy if you need to > block a wireless device but can't actually disable it for some reason. > > An absorber converts the RF to heat. Ferrite beads convert high > frequency magnetic fields to heat. If the signals are enough to heat the > material significantly, then they probably do become less effective, but > unless you're shielding a radar system I don't think you have to worry. > > I think having a metal case is a plus, because some frequencies will be > reduced. > But unless all seams are conductive (a pro enclosure is always welded) and > the cable penetrations are all thoroughly filtered, the RF will get to the > surface. > It's probably more important that the electronics were laid out well, with > good ground planes, good isolation or ground bonding between different > boards, > twisted cables... > > Then you still have the keyboard, mouse and screen to deal with. There are > ferrite-based > absorbers, and mu metal might help, but unless you have some RF or EMC > engineer helping > you, it's better to just stick with the basics. If the computer is really > bothering you, > a big thick piece of aluminum (like 1/2 inch) between you and it should do > it. > > On Wed, Jun 10, 2009 at 1:38 PM, rticleone <rticleone@...> wrote: > > > > > > > This is something which has confused me for some time. When you're talking > > about shielding something from RF, I see mention of conventional shielding, > > which reflects RF; it is conductive. > > > > I also see mention of RF "absorbing" material. Is this material that can > > literally "soak up" microwaves? But if so, can it reach a point where it's > > "saturated" and no longer works? I find this very confusing. > > > > And if a material "absorbs" RF rather than reflecting it, does that mean > > the material needs to be grounded? > > > > Here's my speculation that caused me to think of this...having been > > wondering how the heck to use a small Eee PC with fiber optic cable instead > > of highly electric-field emitting Ethernet cable (which seems like it'll be > > impossible or exorbitantly expensive because the Eee uses, if I'm correct, > > mini PCIe, and for that I'd have to convert to regular PCIe, into whichI'd > > have to stick an extending cable and then a PCIe based fiber optic converter > > card, which go from 200 to over 1000 dollars...arrrrrgh)...I started to > > think... > > > > ...if, ever, it were affordable to have a small laptop built to run > > exclusively on battery, with low voltage components, a regular sized PCI > > slot to use fiber optics easily, ferrite on all wires, etc., etc... > > > > ...I thought, rather than rely on a conductive metal case to keep RF > > inside, what about using a plastic case but coating the inside of it with RF > > absorbing material, or paint? That way the RF generated by the components > > shouldn't radiate out, but the case wouldn't have the conductivity (andthus > > less likely to re-radiate anything electrical plugged into it). > > > > But, it again begs the question: are all RF absorbing materials also > > conductive; and if so, what the heck is the difference between an absorber > > and a reflector? > > > > Thanks! > > > > R. > > > > > > > > > [Non-text portions of this message have been removed] > |
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In reply to this post by R. Ticle
In a message dated 10/06/2009 22:52:04 GMT Daylight Time, [hidden email] writes: Can you convert an electric field into heat using RF, or any kind of material? I would do a happy dance if it could be done! Paul Uk replies - I guess if you can hold the electrons etc long enough in the material they will perhaps group up and vibrate and thus heat up leading to disassemblment of thier former structures and thus radiate as a newly formed frequency that dissapates to the surrounding air molecules via heat transmission and so dillute/demob the initia; wave. only a guess - p [Non-text portions of this message have been removed] |
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In reply to this post by R. Ticle
In a message dated 10/06/2009 22:52:04 GMT Daylight Time, [hidden email] writes: If I was looking at building from scratch (something akin to a laptop), what features in a screen would be the most important, EMF wise? I mean, LED lit LCD, but what about the components that make it up? What's worse and what's better? Could I stick ferrites on the cables that go to the screen? Paul uk - get the pc in a sheilded cupboard, run cables in tested/trusted ground in metal conduit, and go the last mile with optocoupler to mouse and keyboard or go infared, ensure that the pc has the best possible low noise power supply and the screen is backlit on leds and agin has a good low noise psu. Use magnification software such as zoomtext so that the screen can be placed as far away from you as possible but you can still view it comfortably... dont wait until you feel sqiffy when using it get off it long before. [Non-text portions of this message have been removed] |
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In reply to this post by PUK
Holy freakin' technical speculation, Batman!
Sorry, when I said "using RF", I meant, "using ferrite" or any other material. Umm...does your statement still apply? And is this asking the impossible? You can block RF, you can absorb RF; you can prevent magnetic fields with the right material; why the heck can't you shield an electric field without grounding it? There's got to be a way! No, seriously; is what you described even possible? Daft, but very serious,question. R. --- In [hidden email], paulpjc@... wrote: > > > In a message dated 10/06/2009 22:52:04 GMT Daylight Time, > rticleone@... writes: > > Can you convert an electric field into heat using RF, or any kind of > material? I would do a happy dance if it could be done! > > > > Paul Uk replies - I guess if you can hold the electrons etc long enough in > the material they will perhaps group up and vibrate and thus heat up > leading to disassemblment of thier former structures and thus radiate as a > newly formed frequency that dissapates to the surrounding air molecules via > heat transmission and so dillute/demob the initial wave. only a guess -p > > > [Non-text portions of this message have been removed] > |
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In reply to this post by R. Ticle
In a message dated 10/06/2009 23:35:21 GMT Daylight Time, [hidden email] writes: Umm...does your statement still apply? And is this asking the impossible? You can block RF, you can absorb RF; you can prevent magnetic fields with the right material; why the heck can't you shield an electric field without grounding it? There's got to be a way! Paul uk - I guess that the material that is used to halt the passage of elec feild is rather like catching bees in a net you get to the point where they will start coming out of every orrifice unless you can give them a controlled route out, the ground is such a route for electrons etc.. so if you have a big enough material perhaps you can hold back the feild for longer but that said becareful that you dont catch any unwated extras in the bargain, it really is a vicious circle, i think you cant destroy energy but merely change its form, so its all about having the space to live with such consequences and in modern society we are running out of space to fit all our ideas into ! [Non-text portions of this message have been removed] |
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In reply to this post by R. Ticle
I have an older electric range, that I'm concerned about. It works fine, but, I checked it with a Tri-field meter and it gives very high readings in the high and low EMF range. This is with it not turned on. The high field readings are mostly in the control panel, especially near the clock. It is not digital, just a dial set type. There are little or no readings in the electric field on the meter. Just the magnetic fields. There are no readings of any kind, with the circuit breaker turned off.
Do electric ranges usually do this when not being operated, or could the high EMF readings indicate an electrical problem? If this is normal, I won't worry about it. If there could be an electrical problem, I may replace the range. I don't really want to buy a new one, if there is no problem. TIA for any advice you can give me. Donnie |
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In a message dated 10/06/2009 23:51:25 GMT Daylight Time, [hidden email] writes: Do electric ranges usually do this when not being operated, or could the high EMF readings indicate an electrical problem? If this is normal, I won't worry about it. If there could be an electrical problem, I may replace the range. I don't really want to buy a new one, if there is no problem. only person that can confirm this is an electrician, but that said their may well be a motor in the clock section, that gives off emf plus electronics, bassically elec cookers will give off high emf when in use. better off with gas unless you are mcs and have problems with the gas . [Non-text portions of this message have been removed] |
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>better off with gas unless you are mcs and have problems with the gas.
I do have MCS, and can't have any gas appliances, or furnace. Gas really wipes me out, so I have to stick with electric, with all it's faults. Donnie |
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In reply to this post by PUK
Oh gods...
So. Much. Work. I am currently using a system that would leave some other people feeling pretty rotten, and though I know I'd feel better with something improved, I don't know how far I need to go; still, I am being damn picky about it. Is it wrong to want the best when health is involved? As for the monitor, if I go the route of a farther away, battery powered mini-ITX fanless box with aluminum heatsinks, and a separate monitor, I'd already have some of your steps covered, since I'd have (or do it myself/enlist local help if possible) a monitor modified to have LED backlighting, and yank out the bad components, stick 'em in a shielded box, and run it from DC, hence a great reduction in RF and everything else from the screen. I know this monitor could be a hundred times better! I'm certain I'd have a pretty easy time using it if it or another were improved upon as described above. I can't really find info about using optocouplers for mice or keyboards. Have you got anything, or more elaboration? As far as infrared keyboards and mice go, what sort are you referring to? Isee some, but they seem like they're only compatible with PDAs and other such wireless crap. I thought I once read on this list that someone tried out an "infrared" mouse or keyboard, and they found it horrible, or it emitted RF, or some such thing. If you can point me in the right direction I'd appreciate it. What about opening a mouse or keyboard (though it could be tricky, I've tried and failed) and covering the circuitry with non-conductive RF absorber? You know, if I can somehow get this little mini itx box built, I may have the chance for them to stick a PCI card in, and then I'll be able to test what kind of emissions and electric field are generated by PCI-based fiber optic converters... Many thanks again! R. --- In [hidden email], paulpjc@... wrote: > > > In a message dated 10/06/2009 22:52:04 GMT Daylight Time, > rticleone@... writes: > > If I was looking at building from scratch (something akin to a laptop), > what features in a screen would be the most important, EMF wise? I mean,LED > lit LCD, but what about the components that make it up? What's worse and > what's better? Could I stick ferrites on the cables that go to the screen? > > > > Paul uk - > get the pc in a sheilded cupboard, run cables in tested/trusted ground in > metal conduit, and go the last mile with optocoupler to mouse and keyboard > or go infared, ensure that the pc has the best possible low noise power > supply and the screen is backlit on leds and agin has a good low noise psu. > Use magnification software such as zoomtext so that the screen can be placed > as far away from you as possible but you can still view it comfortably... > dont wait until you feel sqiffy when using it get off it long before. > > > [Non-text portions of this message have been removed] > |
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In reply to this post by PUK
Just checked our electric range/stove in the kitchen with a Trifield 100XE.Funnily, the magnetic field on the meter *decreases* when I go over the stove. Weird. Only jumps up when the stove is on. Very little electric field unless touching meter right to stove, even then, not much.
It has a clock, but the clock is digital. Only increases electric field highly when touching clock with meter, and a slight magnetic increase right at the clock. Not a particularly old range. R. --- In [hidden email], paulpjc@... wrote: > > > In a message dated 10/06/2009 23:51:25 GMT Daylight Time, > mickiemc@... writes: > > Do electric ranges usually do this when not being operated, or could the > high EMF readings indicate an electrical problem? > > If this is normal, I won't worry about it. If there could be an electrical > problem, I may replace the range. > > I don't really want to buy a new one, if there is no problem. > > > > only person that can confirm this is an electrician, but that said their > may well be a motor in the clock section, that gives off emf plus > electronics, bassically elec cookers will give off high emf when in use.better off > with gas unless you are mcs and have problems with the gas . > > > [Non-text portions of this message have been removed] > |
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>Not a particularly old range.
R. May I ask what brand of range you have? My husband brought home info on two different brands, with similar features. I'm leaning toward the Whirlpool regular cook top, rather then the Maytag glass top. I am a short and skinny, and I use very heavy cast iron pans. I hate to think what would happen to a glass top, if I fumbled a cast iron pan. LOL The dealer said we can check whatever range I may be interested in, with my meter, at the store. That's a good idea, if I think we need to replace the range I'm concerned about. Donnie |
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In reply to this post by Donnie
In a message dated 11/06/2009 03:55:01 GMT Daylight Time, [hidden email] writes: May I ask what brand of range you have? My husband brought home info on two different brands, with similar features. I'm leaning toward the Whirlpool regular cook top, rather then the Maytag glass top. I am a short and skinny, and I use very heavy cast iron pans. I hate to think what would happen to a glass top, if I fumbled a cast iron pan. LOL The dealer said we can check whatever range I may be interested in, with my meter, at the store. That's a good idea, if I think we need to replace the range I'm concerned about. Donnie Its funny, I checked my set up here, which is a elec oven and separate gas hob which has an elec ignition The hob was knocking out 2mg evan when the switch was off - I think that the hob, connected to the gas pipe is acting as a ground plane for the oven and drawing stray current, so for now the only way I can sort this is to pull the plug and work out what to do, maybe if I bond the 2 together with a wire, that said the gas pipe is touching the oven metal surround? [Non-text portions of this message have been removed] |
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In reply to this post by Donnie
In a message dated 11/06/2009 01:17:36 GMT Daylight Time, [hidden email] writes: Just checked our electric range/stove in the kitchen with a Trifield 100XE. Funnily, the magnetic field on the meter *decreases* when I go over the stove. Weird. Only jumps up when Paul uk replies You might be picking up a feild via your body from say a low volt light/flourescent overhead and when you go to the cooker it drains your aquired feild ? [Non-text portions of this message have been removed] |
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In reply to this post by Donnie
It says on the front:
FRIDGIDAIRE Self Cleaning Convection Oven It uses regular coils for heat, rather than a glass top, which of course emit EMF when they're in use (the coils). When I say not particularly old,I mean, it's not twenty years old, but probably more than just a few; we got it used to replace our truly old one which must have been twenty or thirty years old... R. --- On Thu, 6/11/09, Donnie <[hidden email]> wrote: From: Donnie <[hidden email]> Subject: Re: [eSens] Re: Electric range question To: [hidden email] Received: Thursday, June 11, 2009, 2:54 AM >Not a particularly old range. R. May I ask what brand of range you have? My husband brought home info on two different brands, with similar features.. I'm leaning toward the Whirlpool regular cook top, rather then the Maytag glass top. I am a short and skinny, and I use very heavy cast iron pans. I hate to think what would happen to a glass top, if I fumbled a cast iron pan. LOL The dealer said we can check whatever range I may be interested in, with mymeter, at the store. That's a good idea, if I think we need to replace therange I'm concerned about. Donnie ------------------------------------ Yahoo! Groups Links __________________________________________________________________ The new Internet Explorer® 8 - Faster, safer, easier. Optimized for Yahoo! Get it Now for Free! at http://downloads.yahoo.com/ca/internetexplorer/ [Non-text portions of this message have been removed] |
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In reply to this post by PUK
Hmm, no idea; there's a hood with a fan above the stove, but only has an incandescent bulb in it, and I don't think it was on when I checked; though Ihaven't checked it with the meter. If I find something out I'll post it up.
R. --- In [hidden email], paulpjc@... wrote: > > > In a message dated 11/06/2009 01:17:36 GMT Daylight Time, > rticleone@... writes: > > Just checked our electric range/stove in the kitchen with a Trifield > 100XE. Funnily, the magnetic field on the meter *decreases* when I go over the > stove. Weird. Only jumps up when > > > > Paul uk replies > You might be picking up a feild via your body from say a low volt > light/flourescent overhead and when you go to the cooker it drains your aquired > feild ? > > > [Non-text portions of this message have been removed] > |
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