Re: [CAD_CAM_EDM_DRO] digitizing probe

Thanks, Alan,

I had tried 5v, but in series with a 100 k ohm resistor. It was not
reliable. The probe has stainless steel contacts, I am told, and I was
trying to set up for a long probe life. Noise has not been a problem. I
can watch the signals on my scope. It seems as though the higher voltage is
important. Thanks. I just switched over to the 12 volts, and immediately
on the O scope the switching seems much more snappy.

Thank you again for thinking about my question.

Tom Eldredge

----- Original Message -----
From: Alan Marconett KM6VV <KM6VV@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, June 13, 2001 2:17 PM
Subject: Re: [CAD_CAM_EDM_DRO] digitizing probe


> Hi Tom,
>
> I'm not your "electronics genius", but I'd suggest more like 5+ and a 1K
> resistor pull-up (the parallel port may/may not have one). I believe
> you need a MINIMUM amount of current through the contacts to make them
> operate properly. I don't think you'll get arcing, and I wouldn't use
> the cap. RG-174U (small, .125" coax cable) makes good leads for this,
> if the probe doesn't already have something. Shielded audio cable
> should also work. Since the "opening" of the contacts is a "terminal"
> event (meaning you only need to see the first one), I don't believe the
> debounce is necessary. You could use a Schmitt trigger gate to buffer
> the line (and give a little drive to the parallel port input), but it's
> probably not necessary. I would recommend keeping this probe line AWAY
> from motor circuits, to keep the noise out! Just my opinions. YMMV.
>
> Alan KM6VV
>
>
> Tom Eldredge wrote:
> >
> > Gentlemen,
> >
> > I am not trying to get things going on the digitizing thread again, but
I have a question for you electronics geniuses ( I say that respectfully,
and gratefully):
> >
> > 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.
> >
> > By the way, I am using 12 volts, because when I tried to use 5 volts,
the contact resistance sometimes gave me erroneous indications. I compare
the signal coming from the probe to a reference of 8 volts using an LM339 to
avoid erroneous indications produced by contact resistance. I also use
software to debounce the contacts.
> >
> > Thanks again for your help.
> >
> > Tom Eldredge
>
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