Re: Agilent Encoder Pull-up resistor

It makes a lot of sense to use differential drivers/recievers if MHz
or more signals must be sent.

These signals cannot be effectively low-pass filtered to remove noise
because often the signal period is less than the noise pulse.
Filtering would then remove the signal as well as the noise.

Low and moderate cost optical encoders use photo-transistors. Photo-
transistor frequency respose begins to roll-off above 50kHz at best.
This makes the minimum usable encoder logic 0/1 time 10uS.

Noise is generally pulses narrower than 1uS, so low-pass filtering is
very effective in removing the noise while preserving the signal.

To it makes absolutely no sense to use differential encoders for
reasons of noise reduction. Answer for yourself this question: Why do
drives that use differential encoders also not use differential step
and direction inputs?

Step pulses can have pulse widths at or under 1uS. These pulses
cannot be low-pass filtered for the reasons mentioned. If differental
inputs are used anywhere, they should be used first on the
step/direction interface.

I'd love to hear the reasoning for that.

Mariss



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Peter Homann" <groups@...>
wrote:

>
> Jon,
>
> That's just plain rude and offensive!
>
> The advantages of using differential signals are very clear. It's

the

> reason why it's standard practice in a lot of the industrial control
> industry.
>
>
>
> Note to moderators: I didn't think this short of "Bashing" was

allowed on

> this group.
>
>
>
> Jon Elson wrote:
> > afogassa wrote:
> >
> >>
> >> Rutex new drives needs differential encoders if the distance from
> >>pcb to the motor is over 1 foot or so, rutex has a pcb that
> >>converters the signal from incremental encoders to differential

it's

> >>about 20Us$ or so.
> >> After installing the converter don't use pullup resistors.
> >>I'm using rutex drives and it's very good, little hard to tune it
> >>with software, I like the old ones with pots to set it up.
> >>
> >>
> >>
> > Oh, wonderful! They must be doing something really "SPECIAL" in

their

> > drives
> > to require this. I have several installations with 30 FEET of

encoder

> > cable that
> > work perfectly with single-ended encoders. So, I'm glad I don't

use

> > Rutex drives.
> >
> > Jon
> >
> >
> > Addresses:
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