Re: Need help with O-scope

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Polaraligned"
<polaraligned@...> wrote:

>
> I have had a ton of problems with my Gecko's. Best thing I
> did was to run ALL 3 Gecko power supply grounds back
> to a single point ground. I also use this single point ground
> for my encoders ground, VFD ground, all my shields go there, etc.
> You need to make sure your encoder wires are shielded and kept away
> from the PWM out to the servos. Of course, this assume you are
> using servos.
>
> Scott
>

Scott's star point (single point) ground is one of two methods to
deal with local noise problems. Another is to not use the same
ground for motor voltage (high current PWM signals). By not having
the motor negative tied to signal grounds it eliminates the biggest
source of noise in the system. Encoder runs more than 6 ft need
special attention and need to be run away from any high current
wires. In some cases you need to use differential drive
components. You can isolate the power from the logic in a Gecko
system because they have opto isolated inputs.

If you don't have some experience using a scope then it will be
frustrating. With noise you need to be able to analyse if the noise
is actually there or it is getting into the probe through a long
probe ground or scope ground loop. In circuits with a long AC
ground or a ground loop you have to be able to determine what signal
you are actually looking at and how much noise is getting to the
actual circuit of if the ground on your scope is causing a problem.

Catching random (impulse) noise is like trying to photograph a
bullet. We have started using a Digital Storage Scope and even with
that catching a random errant pulse is not easy. Spikes are easy
since you can trigger on the increased voltage level.

Half of using a scope (after you figure out what all those controls
do and how to set them) is the correct interpertation of the
waveforms.

Proper use of a scope is part science and part art. You first need
to know what a working circuit waveform should look like and how
much tolerance from that you can allow before it starts to cause
problems.

Properly used a good scope is a fantastic piece of test equipment.
It will show you DC and AC volts, frequency, signal waveforms and
even current waveforms with the right probes. It in fact gives you
so much information that it takes practice to make sense of it.

Lets be careful with this thread and not get into generic "How to
use a Scope" electronics discussions. I realize this is about
finding noise in home built CNC systems but discussing basic
electronics and the use of test equipment will move us away from the
focus on the purpose of the list.

Tom Caudle