Re: The mechanism behind bouncing...

On Sat, 03 Feb 2007 08:13:46 GMT, "Jon Slaughter"
<Jon_Slaughter@xxxxxxxxxxx> wrote:


"KILOWATT" <kilowatt"nospam"@softhome.net> wrote in message
news:45c3aa6d$0$31564$c3e8da3@xxxxxxxxxxxxxxxxxxxx
Hi... thanks for your attention.

I just wish to know the precise reason why for example, a digital counter
may count many pulses on it's clock input when the clock is feed via a non
noise-free source like a mechanical switch. It is because when the
contacts
makes/breaks, arcing (i've read somewhere that there can be a possibility
of
arcing even at low voltage) occurs, or if it's because of the very rough
surface (microscopically-speaking) of the switch contacts, were the metal
molecules grinds (and possibly flexes) together, during switch activation?
TIA for your reply.



The atoms of the two materials are not configured in such a way that there
is complete contact. If they were then the materials would be fused. Since
there are not fused and they slide there is friction involved and this
friction causes the contacts to move farther a part and then closer
together. So the average distance between the constants is changing
significantly campared to when is not moving and they are making good
contact. So now the electric field is changing because of the distances
changing between the contacts. As the contacts move farther away the field
becomes weaker but now we have a capacitive effect. This effect creates a
force between the contacts that attract them. One now has a kinematic force
pulling the contacts away(so it can slide), one of friction that wants to
stop the slide, and one of capacitance that is attractive(I'm sure there are
more too).


Sorry, but that's all nonsense. At low voltages and currents, switch
contacts bounce for purely mechanical reasons.

If your field theories were true, the applied voltage would radically
change the bounce waveform. It doesn't. Try it.


Anyways, So there are all these forces that are interacting and the end
result is this oscillation of the contacts moving toward and away from each
other. One always gets "arcing" but thats kinda relative turn. (In some
sense all electronic flow is "arcing".)

Metallic conduction is not "arcing." Arcing is gaseous conduction.
Vacuum tunneling happens too, but the range is just on the order of an
atomic diameter, not important for things like switch contacts.

John


.

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