Re: [CAD_CAM_EDM_DRO] digitizing probe

Jon,

Thanks for the advice. I guess I have been mixed up about the capacitor
across the contacts. It seems that I have often seen some sort of an RC
combination across some contacts in industrial equipment. How does this
component operate?

Thanks for the correction.

Tom E.

----- Original Message -----
From: Jon Elson <elson@...>


> Tom Eldredge wrote:
>
> > Gentlemen,
>
> > I am using a digitizing probe made by Fowler. It is a copy of a
Renishaw cmm probe that the patents have now run out on. It has no debounce
electronics or anything like that, just a set of contacts configured as the
Renishaw probes are. My question is:
> >
> > I am applying + 12 volts through the probe contacts then through a 100
kohm resistor then to ground to protect the contacts from too much arcing.
Should I put a capacitor accross the contacts to further protect them from
arcing? It seems as though a .1 ceramic might help.
>
> NO! The capacitor will store energy, and when the contacts close, it will
deliver the energy to
> a short, causing a very high current. Given the typical wiring, it could
be 100 Amps if the cap
> is real close to the contacts. This will cause pitting even at 12 volts,
and quickly ruin the probe.
> You can probably go with a much lower resistor than 100 K Ohms.
>
> If you need some debouncing, you can put the capacitor on the OTHER side
of the resistor,
> where it will slow down the change in voltage, but not deliver large
currents to the contacts.
>