Re: STG2 Outputs

[Jon Elson <jmelson-at-artsci.wustl.edu>]

JohnDRoc-at-aol.com wrote:

> Does anyone know how to re-assign the DAC's on the STG card.  (Fred and Will
> are on vacation, so I can't ask them.)  I think, by process of elimination,
> that I have a bad DAC - DAC1.  Since this is the Y axis on the machine, it's
> kind of crucial.  Just for giggles I'd like to assign the output to DAC3.  I
> tried changing the offset in the STG2.h file from 12 to 16, but it didn't
> work.  I think there might be more to it.  Thanks.

I think the STG DOS diagnostic program allows you to set any of the
DACs to any digital value.  You should try this.  Just because the DAC
has an offset of +.004 V doesn't sound like a problem.  In fact, it is
most likely working, as the 'zero' output requires the DAC to put out
a voltage halfway between the two extremes.  If there was much wrong
with it, it would not be able to do this.

Do you have an oscilloscope?  IF not, you should hook a pot between a
source of +10 V and -10 V and the wiper going to the servo amp input.
You should be able to make the axis move slowly one direction or the
other by making small adjustments to the pot.

You should also be able to swap a servo amp to a different axis and
see it work.  At least, the last message about this indicated it was
the servo amp, not the DAC.  But, it is possible you have a tach or
encoder phasing issue on your Y axis wiring.  This will definitely cause
the axis to go wild, and slam into the stops.  You should turn the CL
pot to the minimum, reverse the tach wires, and then bring the CL
up very slowly until the axis starts to move.  If the tach phase is backwards,
the axis will accelerate until the current limit is reached.  If the tach
phase is correct, it will attempt to hold position, or move slowly
due to the offset in the input.  Any attempt to move the axis manually
will be resisted by the motor.

Jon