Re: twisting motor cables

--- In CAD_CAM_EDM_DRO@y..., "Brian Punkar" <bspunkar@a...> wrote:

> --- In CAD_CAM_EDM_DRO@y..., "ahlee1010" <ahlee1010@h...> wrote:
> > --- In CAD_CAM_EDM_DRO@y..., "caudlet" <tom@t...> wrote:
> >
> > Would it be correct to say that signal line are more suseptible

to

> > noise because it is only 5V while the motor cable may be way

above,

> > say, 30V? What about motor cable as a source of noise?
> >
> When you twist the motor cables you are not trying to keep noise

out

> of the motor but simply reduce the effects of the noise on the

other

> circuit elements and wiring.
>
> The signal lines are twisted to reduce the effects of induced

noise

> from inductive sources such as the motor drive.
>
> The voltage in a system only matters as a ratio of signal to

noise.

> Input channels where the sensitivity is high are the primary

problem

> sources for cable induced noise. With a sensitive input and a long
> cable you can easily induce transients large enough to become false
> input readings.
>
> The motor is a power device with a very low input impedance it is
> very hard to induce enough noise into the motor cables to actually

do

> anything. The primary source here is the motor drive so you try and
> reduce the interaction between the two phases. Mostly you are

trying

> to keep the motor drive switching out of everything else.
>
> > > a "pair" of wires. That means wires that make up a complete
> > circuit
> >
> > One of the pair goes to ground. Does the return current always
> return
> > via th other pair, or is it possible that the return current may

go

> > via any of the numerous other ground wires?
> >
> > Thanks
> >
> > Lee
>
> In an ideal circuit the current returns down the complementary

wire

> in the signal pair. This however is not always the case as current
> will always seek the easiest path to ground. This is one reason the
> shield is connected at one end only in many cases, this ensures

that

> it acts as a shield and not a ground current path defeating it's
> purpose.
>
> Brian Punkar

That makes sense. Thanks