Re: Signals of a 5V encoder


Haritztolete wrote:
> Hi, I am going to use a 5V encoder of 600 pulses. The signal it gives
> me is a pulse train of 5V and it goes to a driver that is 25 metres far
> away from the encoder. The cable of the encoder goes close to some
> power cables and all the cables are shielded. I don't have any
> experience in such long distances and I would like to know if I could
> have problems with electric noise, and how to avoid it. Thanks a lot.

Hi, Haritztolete. I hope you haven't purchased your encoder yet. If
you haven't, look for one that gives you a line driver output. You can
then set up a line receiver at the other end of the twisted pair line,
and change the signal back into standard digital logic. A standard
open collector output will be a noise nightmare at 25 meters, no matter
what the pullup resistor.

A line driver/line receiver setup will provide quite a bit of immunity
from noise, because the noise is equally coupled into the both sides of
the differential pair if you use twisted pair wire. The difference
between the two voltages will still be the same, and that's what
determines the logic level.

However, you also have to worry about sufficient energy being
inductively coupled into the signal lines to cause damage to the line
driver or line receiver. You really should arrange for different
routing of signal and power lines as a matter of course, shielded or
not.

Trust me on this one. There are few things more dispiriting, or more
likely to evaporate your and others' trust in your electronics
expertise, than creating solutions that kind of work or break down at
random.

Please post back if you have any questions.

Good luck
Chris

.

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