cormack@sequent.UUCP (Michael Cormack) (02/23/90)
In article <3618@sage.cc.purdue.edu> ssy@sage.cc.purdue.edu (Kyler Laird) writes:
%I've recently been informed that I'd better get a Zenith 386-25 off the
%floor or risk the perils of increased static buildup.
%
%Is this a crock? The case is metal. It's grounded. What's the difference
%between it sitting on the floor soaking up static electricity (to ground)
%and sitting on the desk getting a charge everytime someone brushes against
%it?
%
%I'd love a reply so that I can, perhaps, reply intelligently to this.
%
%Thanks...
%
%--kyler
I can think of one reason, how true it is I don't know because I've
never actually tested it out with a static meter.
When your shoes (especially nike's or reebok's) rub against the ground
(or even better a rug), they build up a charge. This is called a
triboelectric effect. Most people realize this by the ZAP they get
from a door knob or equiv. What most people don't realize is that
there is also an electric field associated with this charge and *that*
is probably the reason why it's been suggested to move your tower.
Like I said I don't know how true this is. I use a tower in the lab
and me reebok's are right against it. I haven't lost any data yet.
Hope that helps,
mikessy@sage.cc.purdue.edu (Kyler Laird) (02/27/90)
I'd like to propose an alternate question: Is it possible/probable to damage a shielded, grounded (enclosed) computer with common static electricity buildup? Anything over 16MHz is usually heavily shielded against creating RFI. Wouldn't this shielding prevent external static damage? --kyler
myers@hpfcdj.HP.COM (Bob Myers) (03/01/90)
>I'd like to propose an alternate question: Is it possible/probable to damage >a shielded, grounded (enclosed) computer with common static electricity >buildup? Anything over 16MHz is usually heavily shielded against creating >RFI. Wouldn't this shielding prevent external static damage? Not necessarily; even though a particular system may pass the FCC or VDE requirements for RFI, there is still the potential for damage via ESD. (For that matter, there's still SOME RFI leaking out - it's REALLY difficult to make a system that produces NO or even very little radiated or conducted emissions; just ask the folks who do Tempest* work for a living!) Damage from ESD can occur in at least two ways. The first and most obvious is the destruction of a component via a discharge which sends its current through that device; say, zapping an input on a TTL device. The other, and sometimes overlooked, factor is that even if the discharge goes directly to "ground" damage can still occur. Electrostatic discharges can have pretty remarkable amounts of energy (even if only for a very short time), and the path through your system's "ground" to the ESD's Final Resting Place (call it "earth ground", or the Local Source of the Most Holy Truly Zero Potential) may contain appreciable impedance. If this is the case, the high currents of an ESD zap can induce momentary high-voltage spikes *on the ground of the system*, and thereby damage components. RFI protection and ESD protection are related, but doing a good job for one doesn't necessarily mean you're safe from the other. * - "Tempest": referring to the requirements of certain military/government contracts, etc., which adhere to a set of very stringent emission specs known as "Tempest." The concern here is that the other side (the Bad Guys) can very effectively listen in on what your computer is doing by monitoring the RFI it generates. Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers%hpfcla@hplabs.hp.com | sentient life-form on this planet.