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 Post subject: t42 and EMF radiation
PostPosted: Sat Oct 03, 2009 12:41 pm 
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hi

i dont own an emf measurement metre like the TriField metre. Has someone measure the EMF given off by T42 using the meter or has the knowledge of how much emf does t42 give off?

thanks!


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PostPosted: Sat Oct 03, 2009 2:53 pm 
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I used to work in this area where we had to modify PC's and laptops to reduce conducted (down wires) and radiated (through the air) emissions.

I also used to work for a well known company in their Type Approval department where we had to make sure that products met national and international specs in terms of performance and interference (radiation).

First of all every Thinkpad model will have had to have passed Type Approval for every country it sells into, so they will basically be OK in the emissions area.

Having said that, passing a critical eye over the T4x (and probably virtually all others) range, this is how I see the Thinkpad range:

I'd say that there would be quite a lot of radiated emissions from the front of the screen but less from the rear due to the metal case.

Since the rest of the laptop body is plastic, I'd say that there will be high levels of radiation, and reducing it will be quite difficult and expensive.

The other major problem area is going to be the AC Adapter which because it's a switch mode power supply potentially will have very high levels of radiated emissions, and will be difficult to 'tame'.
It's no coincidence that a well designed power supply has double shielded DC cable to the laptop to try and contain radiated emissions.
Also any such device should have well designed filters to remove the high frequency switch mode component from the DC output.

Running the laptop on batteries presents it's own problems since there is no ground (earth) to conduct emissions away, so you need to rely on a containment strategy.

What are you looking to achieve and do you have a particular use for the right laptop?

If you're looking for a well shielded machine with lower levels of conducted and radiated emissions, I'd look at Panasonic Toughbooks which are of all metal construction with internalised compartments, and from the brief look I've had at them look to be the basis of a 'clean' machine.

The other company I'd look at is the German company Kontron, however they are not cheap but will fulfill your needs for a low radiation platform.

Please note that I've been out of this industry for a number of years so cannot give any further advise but hope this helps.


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PostPosted: Sun Oct 04, 2009 1:03 am 
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poshgeordie wrote:
I'd say that there would be quite a lot of radiated emissions from the front of the screen but less from the rear due to the metal case.

What sort of emissions would be coming from the front of the screen? UV? it would be fairly less compared to a desktop LCD monitor one would guess?
How does the metal casing work, why i ask this is because in the desktop keyboard there is a metal plate underlayed below the circuit sheet, and i can feel a slight buzz in the hands while using it. once i removed the metal plate and replaced it with a stack of papers, it was a fair bit less. maybe that metal plate was conducting the emf from the keyboard pcb to the whole keyboard. removing it might have worked in the sense that pcb is radiating via air only in a much more limited area(around the lights only).
poshgeordie wrote:
The other major problem area is going to be the AC Adapter which because it's a switch mode power supply potentially will have very high levels of radiated emissions, and will be difficult to 'tame'. Running the laptop on batteries presents it's own problems since there is no ground (earth) to conduct emissions away, so you need to rely on a containment strategy.

i was under the impression that running the laptop on batteries would be totally clean so far, except ive not got the chance to try it out because of a dead battery.
poshgeordie wrote:
What are you looking to achieve and do you have a particular use for the right laptop?

Use is personal, just to err on the side of caution/safety. Plus i’ve noticed while using the palm rest for typing for 30-40 minutes the buzzing in the palms and a slight stiffness in the joints and slight swelling of the digits which vanishes fairly fast away from the computer. (im still in my early twenties but used computers for a decade an a half, i wouldnt want this to get worse) :eek:


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PostPosted: Sun Oct 04, 2009 5:07 am 
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The explanation is somewhat complicated but I'll do my best.
irus wrote:
What sort of emissions would be coming from the front of the screen? UV? it would be fairly less compared to a desktop LCD monitor one would guess?

The emissions I'm talking about are Radio Frequency (RF) emissions - the same type that your radio or TV pick up.
The display itself radiates RF frequencies together with harmonics into the UHF range (1GHz +) and because there is nothing to stop them from being transmitted (or radiated), they will come out of the front of the screen.
irus wrote:
How does the metal casing work

Metal acts like a shield, reducing and even stopping those same RF emissions from being transmitted out of the metal casing.
This shielding is dependent on how good the grounding is, and without any or with poor grounding, it could in fact act like a crude aerial (the same as your TV aerial for instance) and could in fact cause emissions from it.
irus wrote:
in the desktop keyboard there is a metal plate underlayed below the circuit sheet, and i can feel a slight buzz in the hands while using it. once i removed the metal plate and replaced it with a stack of papers, it was a fair bit less. maybe that metal plate was conducting the emf from the keyboard pcb to the whole keyboard. removing it might have worked in the sense that pcb is radiating via air only in a much more limited area(around the lights only).

I cannot comment on what the 'buzzing' is in your hands and your comment about the metal keyboard plate could be acting as an aerial.
What I would say is again is that all Thinkpads will have been tested by every country they are sold in to make sure (amongst other things) that any RF emissions are at safe levels.
Also the levels we're talking about are miniscule and would not I imagine be detectable or harmful to the user.
Also it does have to be said that the buzzing could be mechanical vibration that is transmitting through to your fingers. Adding paper could be damping the vibes.
I have a feeling there's a recent post about buzzing on Thinkpads - maybe do a search.
irus wrote:
i was under the impression that running the laptop on batteries would be totally clean so far, except ive not got the chance to try it out because of a dead battery.

Because there are crystals and frequency generating circuits inside every laptop, there will be radiated emissions regardless of whether the laptop runs on batteries or mains.
The difficulty with batteries is that there is no potential path to ground via the mains adaptor so reducing the emissions has to be combination of containment - ie metal shielding, and good circuit design to reduce the level of the frequency generating elements.
Also some of the AC adaptors are two wire mains live and neutral with no earth, so with no earth the laptop design has to rely on the above design elements.
irus wrote:
Use is personal, just to err on the side of caution/safety. Plus i’ve noticed while using the palm rest for typing for 30-40 minutes the buzzing in the palms and a slight stiffness in the joints and slight swelling of the digits which vanishes fairly fast away from the computer.

I've commented on the above. What I do suggest is using an external USB keyboard which will take your hands away from the laptop body itself.

Please keep this in perspective - once again the radiated radio signal emissions will be tiny and its very unlikely to be those which are causing you these problems.


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PostPosted: Sun Oct 04, 2009 6:02 am 
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Thanks for your prompt reply and detailed explanations on emissions
I had gone through the following links
http://www.ahappyhabitat.com/computer.html
http://www.citlink.net/~bhima/emfcomp.htm
and the USB keyboard modification which i was talking about was here
http://www.metacafe.com/watch/1132495/h ... _keyboard/
what do you think about the above modification?
very interesting point about buzzing and vibration and thats probably it! It could be the fan and hdd vibrating/buzzing on the thinkpad.


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PostPosted: Sun Oct 04, 2009 9:12 am 
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I recognise that kind of development modification - aluminium foil was very useful for that.

Can I suggest that if you do that, to put a piece of insulating paper so there's no danger of the foil shorting out on the PCB.

I'll have a good read of the links as well. Very interesting.


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PostPosted: Sun Oct 04, 2009 9:38 am 
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poshgeordie wrote:
I recognise that kind of development modification - aluminium foil was very useful for that.

Can I suggest that if you do that, to put a piece of insulating paper so there's no danger of the foil shorting out on the PCB.

I'll have a good read of the links as well. Very interesting.


i tried the aluminium foil method but the keyboard construction is quite odd so it didnt work but nevertheless while i was open and wrapped in the foil i brought a directional-compass above the foil and it would still spin out of control. (using the compass as an alternative to the trifield meter)

i hope you enjoy the links!


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PostPosted: Sun Oct 04, 2009 4:03 pm 
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All devices are different and it could be that your particular keyboard is not radiating from it's PCB but from, say, the interconnecting lead. Or it may be that the USB port is a high radiating port and needs to be dealt with at source before you begin with sorting out any devices plugged into it.

The test equipment I used was very expensive with special detection devices which would help narrow down the problem.
When trying to shield an area what often used to happen is that it shifted to another area - rather like squeezing a half inflated balloon in one place which then causes it to inflate in another - we used to spend most of our time chasing this balloon effect and it could become quite difficult to cure it.

I would say that you're going to find it next to impossible to know what is causing radiation (if anything) and be honest I wouldn't get hung up over it.
The reason why we shielded the keyboard for instance was for particular applications. Out of the box it was usually a very low emission device and one of the last items we looked at, and often didn't even need to.


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PostPosted: Sun Oct 04, 2009 4:26 pm 
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poshgeordie wrote:
When trying to shield an area what often used to happen is that it shifted to another area - rather like squeezing a half inflated balloon in one place which then causes it to inflate in another - we used to spend most of our time chasing this balloon effect and it could become quite difficult to cure it..


haha thats as funny to hear as is great to know from someone who has dealt with this in a professional setting. Thanks for sharing the experience here! I'll not be hung up over this anymore! :banana:


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PostPosted: Mon Oct 12, 2009 6:22 am 
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if you are that worried make yourself a faraday cage. Regarding EMF radiation, most of which would come from the wifi antenna.

The screen itself shouldn't emit much, since it is a LCD and not a CRT monitor, so the UV emission shouldn't be much given that the CCFL tube is coated properly.

Also, at this sort of power level that is emitted by your laptop, it is not powerful to energize anything on the biomolecular level unless you subject yourself to anything above > 1 Tesla in electromagnetic field, like in a NMR or MRI as the medical field calls it.

Your swelling and stiffness is not due to EMF radiation, but rather the ergonomic of your typing position, and there is also a chance that there is some small electrostatic electricity running through you, which is more probable cause of your swelling and stiff wrist.

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PostPosted: Sat Jul 14, 2012 4:48 pm 
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I posted a new thread about this on the Lenovo forums site:
http://forums.lenovo.com/t5/W-Series-ThinkPad-Laptops/ThinkPad-W520-s-2-Prong-Power-Supply-High-EMFs/td-p/770127


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PostPosted: Sat Jul 14, 2012 5:20 pm 
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I'm not certain that I completely understand the purpose of this thread... but in any case I'd just like to mention that if someone wants an impression of the huge amount of e.g. radiatiated emmission tests required to obtain Type Approval by the FCC, try for fun go to the FCC Search Page and see some of the most recent Lenovo products - including SAR (Specific Absorption Rate) tests and other adwanced stuff.

Being an engineer in the RF, microwave & millimeter-wave world, working for 25+ years with both antennas and power-amplifiers (and, not the least, like the rest of you living in a significantly polluted World!), I have to say that I really couldn't care about the low-power emissions from laptops!

Johan

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PostPosted: Sun Jul 15, 2012 4:40 am 
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I'd forgotten about this topic until now and it's bought back memories of my time in Type Approval back in the early '80's and then more specialist testing of PC's and laptop systems in the '90's.

As you say Johan, there's very little to worry about radiation from Thinkpads and the like since they will have had to pass all the tests before being allowed to sell them.

Like you, I occasionally tested VHF and Microwave tranceiver systems and some of the tests were bizarre to put it mildly; for instance take two transmitters and transmit each into the others output and measure the result. I think we were looking for resulting side lobes which had to be below a certain level WRT the transmitted frequency, but it was an extremely dangerous test for both the measuring equipment and the transmitter being tested!

Back when mobile phones - AKA phones you could use only in a car - were about to be first introduced into the UK (and world) our company, and some unknown company called Vodaphone (think they were called that!!), were picked to go head to head by the UK Post Office (who was in charge of these things then and had a test lab near Liverpool Street station in London), and the one that "won" the contract was to supply the UK with the first phones.

It was absolutely fascinating since part of the Type Approval work was testing each part of the complex handshaking process between the Post Office Base Station and our equipment - ie how the two "talk" to each other before the call is made or received - and I remember as I tested each pulse, getting the design team to blow a new EPROM to make the miniscule timing changes until we managed to get it working perfectly. It took 13 EPROM's I remember!

After all this the "unknown" company got the contract and the rest, as they say, is history!

Apologies for the ramble - life seemed simpler then.....


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PostPosted: Wed Jul 18, 2012 7:33 am 
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lead_org wrote:
Your swelling and stiffness is not due to EMF radiation, but rather the ergonomic of your typing position, and there is also a chance that there is some small electrostatic electricity running through you, which is more probable cause of your swelling and stiff wrist.


Without reaching anywhere near the other poster's engi/techie nerd level ( :wink: ), I must say this was also my first thought. There's a lot of people that have problems like numbness, stiffness of joints etc etc due to the ergonomics - or lack thereof - when using a computer.

If I were the OP, I would start by trying an external keyboard and mouse, plus have a good look at the other parts of ergonomics while working at the computer (e.g. relative height of chair and table/computer etc).

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PostPosted: Thu Jul 19, 2012 2:41 am 
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Carpal Tunnel Syndrome comes to mind: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001469/

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