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.

---
That's not true.

When the contacts come to rest after the bouncing period is over
they will either be in intimate contact or they will be completely
separated.
---

If they were then the materials would be fused.

---
Which, indeed, they are until the coil is de-energized and the
return spring exerts force on the armature, breaking the microscopic
weld(s) and allowing the contacts to open.
---

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.

---
No. The friction you're talking about is only about the contacts
rubbing against each other when they're making or breaking and is a
second order phenomenon compared to bounce, which occurs when the
contacts alternately make and break when the coil is energized.
Bounce also occurs when the armature is de-energized, but to a
lesser degree, and is caused by the moving contact skipping across
the stationary contact when the coil is de-energized.
---

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).

---
No. The high-level bouncing behavior is due only to the gross
mechanical characteristics of the contacts and has vanishingly
little to do with the microscopic effects, which are at least six
orders of magnitude smaller than the mechanical effects, I'd guess.

Do you have some hard numbers which would prove otherwise?


--
JF
.