Ignoramus6355 wrote:

The more disconcerting news is that if a tach cable is not connected,
the drive goes into a runaway mode EVEN IF NO INPUT SIGNAL is
present (inputs shorted to each other).

This means that if I do a shoddy job wiring those tach contacts, or
the open barrel terminals fall out, or anything else, I will be in a
world of hurt.

I know that EMC has some protection against following error, but I am
not sure how robust is that.

Make sure the encoder wiring is good or your control has no way to know you have an axis
that is running away. The only thing your control can do is put your system in e-stop.

I had a waterjet cell that profiled headlinders for explorers. The drives were DC and
used a tach. I always kept in mind that one wire broken could cause a lot of grief and
danger. Not a real problem to the operators but if I'm inside teaching a profile, I
better be somewhere a run away can't get me.

As far as your tach, have you opened the motor and looked at the brushes? If the brushes
are worn down, trouble is on the horizon. I've never had problems with tach brushes
during the time period I had to deal with dc drives, usually the motor brushes that have a
more demanding task fail. Oh, while you are in there, blow out the dust.


Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller