Re: [CAD_CAM_EDM_DRO] AGND+DGND+EARTH=NOISE....true or false?

Babar wrote:

> Hi All,
> In our Hurco Milling Servo drives are such that
> digital and analog grounds are internally shorted i.e
> DAC output of STG,tacho of motor ,limit switches and
> encoder have common grounds which are then tied up to
> Machine's body which is connected to earth, We are
> facing problems of Noise I was wondering if this is
> the reason ??

It could be. What type of noies, ie. what are the symptoms?

I designed a 3 to 5-axis servo drive system for my mill conversion, and decided to
use common supplies for the motors and control/logic. I knew ground loops were
a likely result, so i put high-quality instrumentation amps (Analog Devices AD620)
on the velocity command and tachometer inputs. I already had used these in
other projects, and knew they had an astounding capacity to reject common-mode
noise. Even if a signal source was single ended, I could sense the ground potential
at the source and remove common-mode noise that had coupled into the ground
and signal wires. It has worked remarkably well.

It may be good if you can break the ground at the milling machine, and only have
the computer ground used for all the devices. Then, you can put in one heavy
ground wire between the computer case and the Hurco machine base. This
should at least simplify the ground loop situation.

Jon