Human Body Capacitance and Resistance
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From: Tim Williams on 2 Jun 2010 15:19 "Archimedes' Lever" <OneBigLever(a)InfiniteSeries.Org> wrote in message news:o39d06l00ql0s72144sfjhmvgmuhs9gcon(a)4ax.com... >>Bodies certainly have skin effect. > > Not at line frequencies, they don't. Idiot. > >> That's one reason high-frequency >>current burns skin but doesn't penetrate to internals. > > No, that is NOT the reason why, idiot. Nor does it number among the > reasons why. http://en.wikipedia.org/wiki/Tesla_coil#The_.27skin_effect.27_and_high_frequency_electrical_safety "Although skin effect limits Tesla currents to the outer fraction of an inch in metal conductors, the 'skin depth' of human flesh at typical Tesla coil frequencies is still of the order of 60 inches (150 cm) or more." Check your facts, John. ;-) >>All conductors have skin effect. > > All metallic conductors have a skin effect at high frequencies. > > Bulk mediums like a carbon comp resistor and like human flesh do not > "conduct" the same way that a formed wire does. Actually, they do. Skin effect is due to eddy currents. Alwayswrong is always wrong. ;-) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Archimedes' Lever on 2 Jun 2010 17:25 On Wed, 2 Jun 2010 14:19:18 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >Actually, they do. Skin effect is due to eddy currents. Alwayswrong is >always wrong. ;-) > >Tim The flow in bulk mediums differs from that of solid, metallic conductors. The eddy current propagation and the flow itself differs. The 'skin effect' differs.
From: Don Klipstein on 2 Jun 2010 21:57 In article <86k5siF7jmU2(a)mid.individual.net>, Dirk Bruere at NeoPax wrote: >On 01/06/2010 01:09, Winfield Hill wrote: >> Dirk Bruere at NeoPax wrote... >>> >>> On 30/05/2010 12:49, Winfield Hill wrote: >>>> A repost of a comment I made elsewhere, for discussion here. >>>> >>>> The subject is ESD Human Body model values. I'm enamored by >>>> a 1989 symposium paper by Richard Fisher, of Sandia Nat'l Labs, >>>> where he created a "Severe Human ESD Body Model." His model >>>> had worst-case numbers meant for use in electrostatic-discharge >>>> circuit-protection analysis, etc. >>>> >>>> Fisher's Severe Body Model consists of two parts, the body and an >>>> arm with hand reaching out to zap something. The body part has >>>> 400pF of capacitance in series with 250 ohms and 0.5uH. Then the >>>> arm and hand part bridges the body terminals with 10pF, and finally >>>> we have another 110 ohms and 0.1uH in series to complete the model >>>> and connect it to the poor real-world victim. The body capacitance >>>> is higher than you may see elsewhere first because the body is >>>> sitting down, and second because it's a worst-case body. We won't >>>> go further into what that means. :-) >>>> >>>> You charge the 400pF capacitor to a voltage of your choosing. >>>> 20kV is a nice high number. During discharge we get a fast spike >>>> of current from the 10pF, with sub-ns risetime to dangerous levels, >>>> with up to 5A peak current, and lasting up to 5ns into the "load." >>>> This is followed by a slower discharge of the 400pF capacitance, >>>> lasting up to 200ns. >>>> >>>> This would be followed by, ahem, a postmortem. >> >>> Well, since people regularly charge themselves up to at least >>> 30kV (a 1 cm spark) I would say not. >> >> Right you are. As I clarified earlier, I was thinking of a >> component postmortem. > >Also, given the hypothesized rapid rise time, doesn't most of the >current flow on the surface ie skin - a literal "skin effect"? I would apply to the above a combination of Fourier transform for a frequency spectrum analysis, combined with the skin effect formula. Please keep in mind the DC component of a quick DC pulse or a quick asymmetric AC pulse! A short unipolar pulse is roughly as bad as 50-60 Hz AC! In addition to AC component at frequencies in spectral analysis at frequencies near/below 1 KHz or 400 Hz or so, and frequencies from around 1 to 20 KHZ get deweighted rather than discounted! -- - Don Klipstein (don(a)misty.com)
From: JosephKK on 7 Jun 2010 02:59
On Wed, 02 Jun 2010 10:08:37 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 01 Jun 2010 11:33:43 +0100, Dirk Bruere at NeoPax ><dirk.bruere(a)gmail.com> wrote: > >>On 01/06/2010 02:32, Mycelium wrote: >>> On Tue, 01 Jun 2010 00:18:18 +0100, Dirk Bruere at NeoPax >>> <dirk.bruere(a)gmail.com> wrote: >>> >>>> On 30/05/2010 12:49, Winfield Hill wrote: >>>>> A repost of a comment I made elsewhere, for discussion here. >>>>> >>>>> The subject is ESD Human Body model values. I'm enamored by >>>>> a 1989 symposium paper by Richard Fisher, of Sandia Nat'l Labs, >>>>> where he created a "Severe Human ESD Body Model." His model >>>>> had worst-case numbers meant for use in electrostatic-discharge >>>>> circuit-protection analysis, etc. >>>>> >>>>> Fisher's Severe Body Model consists of two parts, the body and an >>>>> arm with hand reaching out to zap something. The body part has >>>>> 400pF of capacitance in series with 250 ohms and 0.5uH. Then the >>>>> arm and hand part bridges the body terminals with 10pF, and finally >>>>> we have another 110 ohms and 0.1uH in series to complete the model >>>>> and connect it to the poor real-world victim. The body capacitance >>>>> is higher than you may see elsewhere first because the body is >>>>> sitting down, and second because it's a worst-case body. We won't >>>>> go further into what that means. :-) >>>>> >>>>> You charge the 400pF capacitor to a voltage of your choosing. >>>>> 20kV is a nice high number. During discharge we get a fast spike >>>>> of current from the 10pF, with sub-ns risetime to dangerous levels, >>>>> with up to 5A peak current, and lasting up to 5ns into the "load." >>>>> This is followed by a slower discharge of the 400pF capacitance, >>>>> lasting up to 200ns. >>>>> >>>>> This would be followed by, ahem, a postmortem. >>>> >>>> Well, since people regularly charge themselves up to at least 30kV (a 1 >>>> cm spark) I would say not. >>> >>> >>> Except that he was referring to the chip. D'oh! >> >>OK - I get it now! >>I did that once with an expensive chip. >>A guy passed it to me and, unthinking, as I went to take it there was a >>big fat spark that leapt through its pins. Straight to the rubbish bin. > >I touch the other person, to equalize our potentials, before handing >off anything that might care. Ditto touching a metal workbench. > >John Oh yeah. Back in the early 1970s i kept sensitive MOS the cards in the factory black plastic bags and equalized (touching he other hands) before handing it over in the bag. So on and so forth. |