G-Gnome has kindly redirect me here. So, hopping everyone on this forum know the orac³( ) I just make a copy/paste: ...but I have a question that lay in my mind for a long time , but this question is realy lame and nearly useless. but I can't help to ask it, or i'll never sleep again... So, let me explain: you probably know the "cage of Faradey" (sorry if I spell wrong the name). To make short, when electricity pass through a metalic box, there is no electricity on the intern surface of the box, only on the outside surface. For exemple, when a light hit a car, people inside of the car won't be electrocuted and will be totaly safe. The same happen for a magnetic field: the magnetic field pass through the box and can be detect on the extern surface of the box, but inside there won't be any magnetic field, even near the surface. So here is my question: is the orac³ EMP-proof? I mean, all the electronic component are in crhomed boxes (chrome is a conductor) and the outside wires are in metalic tubes. It seems that G-Gnome are going to chrome everithing. So even if we put a powerfull magnet near the case (it's realy bad for a normal PC, it affect the processor, the hard drive can be erased and even be break by this way), Would it cause no effect? For a pratical exemple could th orac³ work near a medical-magnetic scanner? The (little) holes would not cause problem (as the exemple of the car, the holes for the glass are tough enoug little to protect the people inside). Hey I had said it was a useless question and I'm not sure G-Gnome could answer this one. but if someone has a good knowledge in magnetic field could he answer me? Thank for the answer
If you put a powerful magnet near a normal case you will loose data, and corrupt hard-drives. In the case of a car, the metal body of the car acts as a conductor of electricity, and sine you, the passenger are inside it you will not get shocked, if you try to step out however you will be fried. I read a story one about a school bus that rammed a hydro-pole and had a high tension wire fall on it. The Metal bus acted as a conductor keeping the children inside safe, however if they had both touched the bus and the ground, that would have been a neasier path than the tires to ground. In the end the driver and a bystander had to throw and catch the children out the door. In the case of the case, its the same, the case (cage) is grounded, so any current induced by EMI will have a path to ground. G-gnome's Orac3's chromed boxes will not work I think in the same fashion, because they aren't grounded. EMI isnt really a problem anyways because all electronic devices are required to "not transmit EMI", the downside is they must accept any interference they recieve. I am not an electronics expert, look for Zap to correct me...
GUIGUI. Here's a quick explanation of a faradays cage - I couldn't find anything better.Faraday's Cage The cages are a good protector against EMP because as the emp wave hits the cage it induces an electrical current, this current is induced in such a way that it generates a magnetic field with an opposite polarity to the EMP wave. These two magnetic fields cancel out within the faradays cage (well thats simplified but its true enough) and hence you detect no magnetic field in the centre and your electronics are safe. BUT, if you place a magnet next to the faradays cage, then after a little time to settle the cage will not block the magnetic field at all. This is because the stationary magnetic field does not induce a current into the cage, and thus does not produce the opposing field. If you place a strong magnet next to an HDD and then leave it there, it will die, but if you just sweep it across the drive quickly it will most likely survive due to the metal shell working as a good faraday's cage. Similarly an AC electromagnet would also not damage the drive, but a DC one would. (Please don't try it though, and if you do its your responsibility). If you put a large magnet next to Orac3? It would damage it as it would any other magnetically sensitive device. A large or small faraday's cage should work in the same way. Btw, with lightning and a car - that's perfectly safe unless it ignites the fuel in the tank (which is known to happen). Hope that helps.. Z.
An EMP would totally destroy G-gnome's latest mod, only a COMPLETELY sealed unit would stand a chance of survival. Areas such as the molex and SATA power connectors would be vunerable to the pulse. Google "tempest" and have a look at some of the shielding measures that need to be taken.
BadOldMan, Actually you are wrong about the need for it to be completely sealed, its not true, all you need is for a path for the current to flow in line with the propogation of the EM pulse - hence why a faraday's cage works, there are lots of holes. I think actually that if you got it right then a hoop of mesh would provide shielding in its centre if it was aligned with the EMP source. I had a look for your tempest (btw, being that it produces a lot of garbage, it would have been better to provide a link to a site that supports your claims) all I could really see is a number of anecdotal claims, no technical evidence and what I believe to be primarilly a conspiracy theory. And unfortunately not really related to EMP, but to remote electromagnetic eavesdropping - EMP and minute electromagnetic fluctuations are very very different (EMP is relatively easy to shield against). I mentioned in my previous post that a permanent magnet (or DC electronmagnet) would actually penetrate a faraday's cage - eventually (due to energy loss in the cage - and this means that some EM radiation will always leak out - it can't be prevented). Nothing is 100% efficient, some magnetic energy will get through the cage, but it will be several orders of magnitude less. You are correct in your belief that solid boxes are better than cages for EMP defense, because they are more efficient (current can follow more accurately the correct course) but any cage can be overcome, once you exceed the current carrying capacity of that cage. I'm pretty sure that the Orac3 box would be ok in all common situations. Even some uncommon ones, as long as it doesn't exceed the carrying capacity of the chroming. (Yes the cabling joints are weak spots because there isn't much in the way of electrical contact, but its covering enough to be effective I think). Z.
As the Tempest standard relates to communications security it does, by association, also relate to EMP. have a look at the second paragraph under the heading of "Problem" http://www.cecer.army.mil/td/tips/product/details.cfm?ID=78 This implies that a complete shielding is required just for EMI Oh and yes there are a HELL of a lot of conspiricy pages out there, and I noticed that the information is nowhere as available as it was 4 years ago...
BadOldMan, Read that, I wasn't being totally clear in what I said, but let me quote from the second paragraph... This states that you do not need to enclose the item, merely block it from the direct path. Ie that it doesn't need to be totally covered. Which is true, but that is using a different principle than that of a faradays cage, that is blocking via absorbtion. In general since you don't know what to shield from, you enclose the entire thing. A faraday's cage is a slightly more specific implementation in that you utilse the side-effects of magnetic eminations passing through a conductive loop to induce a current. According to Lenz' law the induced current generates a magnetic field in direct opposition to the original field. This creates (through cancellation) a magnetic dead-zone within that loop (since the current conducts around the loop) but the magnetic field causing the problem appears to pass through the loop untouched. The induced current just needs to follow approximately the correct loop in order to shield, hence a cage which covers most paths works well - a solid wall would work better. But it does demonstrate that it does not require a hermetically sealed box to work, but that a partially sealed enclosure will work less efficiently. Here's something to help: Faraday's and Lenz's Law Z.
Just a small point, but all (incl the vfd) of my chrome boxes are earthed - via the many many jack sockets whose GND (the outside of the socket) contacts the chrome casing. I designed it to be this way. Even the box on the PSU is earthed through the bolts fixing it to the PSU cover (also earthed). I know my comp will still be nuked by a big EMP, but in the absence of WWIII I think it'll be ok. Would a side-window in an all-metal case render such a case vulnerable to this sort of thing?
G-nome, Yep, case windows do make the box more vulnerable (But only if the EMP comes from a particular direction) - and also mean more EMI escapes. One solution is to use some metalised window tint, and link it with the panel so you have a complete circuit (but it wouldn't be able to handle as much). It was mentioned / covered somewhere in the Macro Black thread.. Just FYI. Nice case btw Z.
I saw on Mythbusters they built a faraday cage for a test using brass screen. It was funny, for a basic test they used a cell phone, and it indeed did lose signal in the cage. Would a wire mesh inside of the case help even though there is already a metal case?
