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Guest PoRrEkE

what not to do with a multi-meter

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Just learned in school that there once was an US-army-dude that thought to be experimentive for a change.He wanted to measure his internal resistance with a MMeter.9VIf you take 90 Ohm for blood that's already a lot.9V / 90 Ohm = 100mAThat's enough to make your heart fibrilate.He made a holl in fingers from both hands and put the pins of the MMeter in them...Don 't try this at home :(

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Philippe, your post count has reached the boeing...Anyway.... sorry but i don't understand this joke :(Anybody happens to touch both pins of a tester, and nobody dies...What gives?And by the way, what multimeter on earth does use 9v????They are powered by a 9v battery, but no mmeter on earth can and will "emit" 9v on its testing pins.It would damage many delicate components.

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The multimeter is not a DC current source that holds steady 9V in its test probes. Even if it was, it would be entirely safe to hold the pins. Human resistance is variable (see table below), but with the best case scenario (dry hands) it's about 1 Megaohm. Taking into consideration that 60mA is a current value that will cause pain (but muscle control still preserved) for DC voltage, one would need:U = RxI = 1 000 000 ohm x 0,060 A = 60 kV of DC voltage to get to the point where it becomes dangerous. The worst case scenario is when a foot is immersed in a conductive liquid. In that case, the human resistance is about 100 ohms. With that resistance:U = 100 x 0,060A = 6 VDC !!In this latter case, we have to consider that the voltage source has to be steady, and the person receiving the steady voltage should be standing in water.To close this little dilemma, it's sufficient to say that the multimeter only emits a small test current from its test probes to run a resistance test. No harm will come from touching those probes, even with a foot in water :).Body resistance:Wire touched by finger: 40,000 Ω to 1,000,000 Ω dry, 4,000 Ω to 15,000 Ω wet. Wire held by hand: 15,000 Ω to 50,000 Ω dry, 3,000 Ω to 5,000 Ω wet. Metal pliers held by hand: 5,000 Ω to 10,000 Ω dry, 1,000 Ω to 3,000 Ω wet. Contact with palm of hand: 3,000 Ω to 8,000 Ω dry, 1,000 Ω to 2,000 Ω wet. 1.5 inch metal pipe grasped by one hand: 1,000 Ω to 3,000 Ω dry, 500 Ω to 1,500 Ω wet. 1.5 inch metal pipe grasped by two hands: 500 Ω to 1,500 kΩ dry, 250 Ω to 750 Ω wet. Hand immersed in conductive liquid: 200 Ω to 500 Ω. Foot immersed in conductive liquid: 100 Ω to 300 Ω. Tero

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eum ...i told ya .. he put the pins TROUGH his fingers.that means:if you touch the pins as we all do, then you got your skin touching them .. skin has a high resistance value, while blood is a liquid and does not!and it is no joke.and if you think it's no 9V, take 2 mmeters and measure how much it is, then let me know, ok? if you got no 2, I will find one of a fellow student and measure it cuz now I am curious to know.

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as i replied to other post:he measured not his external (skin) resistance but his INTERNAL resistance meaning you should add to your table the resistance of blood .. which is a liquid and will give for sure less than 90 ohms.other than that, DC is as you say much worse, but AC can kill you just as well if you go over 110mA and over 90mA if you are alone and no'one is there to cut the power.

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FYI:BODILY EFFECT DIRECT CURRENT (DC) 60 Hz AC 10 kHz AC--------------------------------------------------------------- Slight sensation Men = 1.0 mA 0.4 mA 7 mA felt at hand(s) Women = 0.6 mA 0.3 mA 5 mA --------------------------------------------------------------- Threshold of Men = 5.2 mA 1.1 mA 12 mA perception Women = 3.5 mA 0.7 mA 8 mA --------------------------------------------------------------- Painful, but Men = 62 mA 9 mA 55 mA voluntary muscle Women = 41 mA 6 mA 37 mA control maintained --------------------------------------------------------------- Painful, unable Men = 76 mA 16 mA 75 mA to let go of wires Women = 51 mA 10.5 mA 50 mA --------------------------------------------------------------- Severe pain, Men = 90 mA 23 mA 94 mA difficulty Women = 60 mA 15 mA 63 mA breathing --------------------------------------------------------------- Possible heart Men = 500 mA 100 mA fibrillation Women = 500 mA 100 mA after 3 seconds --------------------------------------------------------------- Putting the electrodes inside your skin, into the blood stream sounds weird, but I guess the effect could be what you say, ie. 90 ohms. I need to think about this.. :)Tero

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