Re: [CAD_CAM_EDM_DRO] Re: CNC Pulse jitter?

Patrick Mendiuk wrote:

> Jon,
> Has you or anyone else measured jitter with EMC?

Well, mostly I have been looking at servo update cycle jitter,
and step timing jitter with my stepper rate generator chips.
EMC's jitter on the servo update cycle is about 10 uS on a
100 MHz Pentium classic, and under 5 uS on a 333 MHz
Pentium II. With a 1 KHz servo update cycle, that is under
1%, which sounds pretty good.

My step rate generators have excellent timing, with the pulse
ALWAYS within 100 nS of where it should be. I don't have
equipment to measure jitter down in this range, it is basically the
jitter of the 10 MHz crystal oscillator. The logic can cause up
to 25.5 uS (user programmable) delay on one step pulse, when
a change in direction occurs too close to a step pulse. This doesn't
throw off the whole pulse train, it just delays ONE step pulse.
Anyway, direction changes should only occur near zero speed,
so it is mostly a non-issue.

HP (now Agilent) has a really nice "time and frequency domain
analyzer" that runs $25,000 that would be real nice for checking out
stuff like this, but I don't have that kind of money!

I will have to check out steppermod.o and freqmod.o and compare.

Jon