RE: [CAD_CAM_EDM_DRO] Need help with O-scope

I thought Marriss would have replied to you by now, since your were involved
with gecko drives.



The need for a transformer all depends on how you have your machine wired,
but should not really be required.

Most of us will have our 0V signals commoned to the earth back panel or the
star earth point in our machines, so earth, the croc clip lead on the scope
probe should be at the same potential and no transformer is needed.

I would tend to run the scope from the same mains supply as the mill, with
it's earth tethered to your star earthing point. It's easy in a workshop to
have a dedicated supply for the mill, and then plug the scope into a
separate wall socket where there could be some ground potential between
them. What looks like noise may not be in the machine, but from the mains
supply outside. Same thing applies to your PC which should also come from
the same supply as the mill.



If you are still unsure, you power up your scope, then use a small
electrical meter to measure the voltage between the earth of your machine
and the scopes earth, and again between the 0V of the area you want to look
at and the scope. Use the meter in AC and DC mode, there should be very low
reading a few millivolts, if so you are safe to attach the croc clip/earth
of your scope probe. If you do find a measurable voltage, it is probably
your source of noise, resulting from a poor earth connection somewhere

With the scope commoned to the star earth point you can also look at your
earthing system to trace out from that point looking for noise on one
connection effecting another.



We would only normally use an isolation transformer if we wanted to measure
a small signal ontop of another large voltage or where a live chassis like
an old valve TV is used. The technique is very dangerous since the whole
body of the scope sits at that dangerous potential, it is preferable to use
the transformer on the appliance and not the scope, or to swap the mains
wires so the chassis is at neutral (same as earth) potential. Really this
only applies to TV's and old valve stuff, we don't work like this in the
modern day.



Hope this helps



Regs Mark





Dr. Mark Vaughan Ph'D. B.Eng. M0VAU

Managing Director

Vaughan Industries Ltd, reg in UK no 2561068

Water Care Technology Ltd, reg in UK no 4129351

Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
Phone/Fax 44 1872 561288

RSGB DRM111(Cornwall)

_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Ed
Sent: 14 April 2007 16:10
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Need help with O-scope



I am having a problem with a mill set up with Gecko drives. There seems
to be a noise problem that has cropped up on the Z axis and I would like
to look at it with a scope. I have the use of a scope but have not used
one for several years and have forgotten a few things. The part I worry
about is; do I have to use an isolation transformer to keep from popping
an IC do to different ground potentials? The scope is a B K Precision
model 1570A with API 1X and 10X probes. Any help appreciated. Ed.





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